Tag Archives: phylogeny

The Botanist in the Root Cellar

How much actual root is in “root vegetables”?

The wintertime pantry is a study in vegetable dormancy. Our shelves brim with structures plants use to store their own provisions. Each embryonic plant in a seed—the next generation of oats, quinoa, dry beans, walnuts—rests in the concentrated nutritive tissue gifted to it by its parent. The starchy flesh within the impervious shell of a winter squash is alive, as are apples, hopeful vessels of seed dispersal. Maple and birch syrup are stored energy made liquid and bottled. And then there are the so-called “root vegetables.” The term covers a surprisingly anatomically varied set of nutrient storage structures, only some of which are actual roots. Our familiar root vegetables represent only a sliver of global plant species diversity but nonetheless include the majority of contrivances herbaceous plants use in order to live to sprout another season: taproots, hypocotyls, stem tubers, root tubers, corms, and rhizomes. Raiding your root cellar for the ingredients for a roasted root vegetable medley, then, provides a great opportunity to turn your dinner prep into a botany lab. All you need is a knife and cutting board.

Roasted stacks of sweet potato and parsnip, painted with sage butter and roasted. See Katherine’s sweet potato post for the recipe.

The case for tree thinking

First we need to consider the taxonomy of our candidate botanical subjects. Taxonomy is the scientific practice of grouping related organisms in hierarchies of similarity. We shove the continuous variation of living things into discrete boxes labeled species, genus, family, order, and so on. Carl Linnaeus started the taxonomic naming system two hundred years before Watson and Crick identified the double helix shape of deoxyribonucleic acid (DNA), marking the beginning of the genomics era. Modern practitioners bring many types of data—geography, fossils, genetics, morphology–to bear toward the twin goals of illuminating the pattern of plant species evolution and defining groups based on common ancestry.

A phylogenetic tree of the major plant clades. Each branch point (node) represents the common ancestor of the organisms on the descendant branches. A single food plant species is shown here at the tip of each branch, a sort of mascot for its lineage.

The visual embodiment of this effort is the tree of life (cladogram) that represents the pattern of plant species evolution by common descent (phylogeny–see our primer on reading phylogenetic trees and using them to understand broad patterns in plant evolution). Each branching point on the tree is a node that represents a common ancestor of all the descendant taxa on the branches that come from it. The species are like the leaves on the tips of the branches. A schematic tree of life is the only illustration in Charles Darwin’s On the Origin of Species, the landmark book that provided the kernels of the core theories of evolutionary biology. Modern scientific convention tries to match old taxonomic names—because they are familiar and useful as a practical matter–with nodes on the tree of life. Small branches connect species to genus. Larger branches connect genera to families, families to order. The deep internal named nodes show the origin of the major clades. A clade is a group of organisms that descend from a common ancestor. A major clade is a significant branch on the plant tree of life that scientists have named for convenience of reference. You may remember some of these from biology class, like “monocot” and “dicot.” The former (monocots) has held up as a robust clade, but dicot is more complicated.

Green garlic, a monocot that stores its winter provisions as a bulb

As it happens, plant taxonomy before the advent of genetic data was reasonably accurate.  Even though our understanding of plant species evolution is far from complete, genomic analysis has provided few big surprises about common ancestry of plant species and membership of taxonomic groups. Early taxonomists had the wisdom to rely primarily on similarity of reproductive structures—seeds, fruit, flowers, spores, cones—to circumscribe named groups. Reproductive structures tend to change more slowly over evolutionary time than do vegetative structures in plants. So one may expect to find a fair amount of coincident similarity among distantly related species in roots, shoots, and leaves.

This is where our categorization of root vegetables by taxonomy collides with our categorization of them by morphology. In short order we will organize our root vegetable species according to which structures the plant has chosen to amplify as a subterranean or soil-adjacent storage organ. This is not the same pattern as taxonomic organization. Grouping our root vegetables by taxonomy first helps us understand similarity and difference within and between groups of closely related plants—families, in this case. In doing so we can develop gestalt for the culinary qualities within plant families and appreciation for the evolution of plant diversity evident on our own dinner tables.  Consider this intellectual nourishment, or perhaps the advent of a lens with which to view familiar foods anew.

Placing root vegetables on the plant tree of life

Around the globe humans utilize many dozens of plant species that bear underground (or near enough) storage structures. The most recent generations of people overwintering in the United States or Europe, however, chiefly engage with only a few. Perhaps only the most dedicated winter vegetable enthusiast will be familiar with all of the species on the following roster of root vegetables potentially available in Western grocery stores or farmer’s markets, although the list is unlikely to be exhaustive. I have organized the root vegetable species by families, and the families by major clade. Our list includes 15 of the 446 currently recognized plant families.

Whole sweet potatoes (Convolvulaceae)–NOT yams (Dioscoreaceae), NOT potatoes (Solanaceae), and NOT oca (Oxalidaceae)

Please take note of the disambiguation about the words “yam” and “potato.” The tubers marketed as “yams” in most American groceries are mostly actually sweet potatoes, which are also not potatoes. True yams are large tubers that are staples of tropical diets but relatively scarce in northern diets or groceries. In New Zealand the Andean oca is also known as “yam.” All of these are in different plant families.

Monocots:

  • Amaryllis family (Amaryllidaceae): onions and shallots (Allium cepa), garlic (Allium sativum), leeks (Allium ampeloprasum), and other alliums
  • Ginger family (Zingiberaceae): ginger (Zingiber officinale), turmeric (Cucurma longa)
  • Dioscoreaceae: true yams (several species in the genus Dioscorea), including the purple yam (ube; D. alata).
  • Sedge family (Cyperaceae): water chestnut (Eleocharis dulcis)
  • Arum family (Araceae): taro (Colocasia esculenta)

Eudicots: asterids

  • Goosefoot family (Amaranthaceae): beets (Beta vulgaris)
  • Sunflower family (Asteraceae): salsify (Tragopogon porrifolius), burdock root (Arctium lappa), sunchokes (Helianthus tuberosus)
  • Carrot family (Apiaceae): carrots (Daucus carrota), parsnips (Pastinaca sativa), parsley root (Petroselinum crispum), celery root (Apium graveolens)
  • Morning glory family (Convolvulaceae): sweet potatoes (Ipomoea batatas; often mistakenly called “yams” in the United States)
  • Nightshade family (Solanaceae): potatoes (Solanum tuberosum)

Eudicots: rosids

  • Spurge family (Euphorbiaceae): cassava (manioc, yucca; Manihot esculenta), the source of tapioca
  • Mustard family (Brassicaceae): turnips (Brassica rapa), rutabagas (Brassica napus), kohlrabi (Brassica oleracea), radishes (genus Raphanus), horseradish (Amoracia rusticana), wasabi (Eutrema japonicum), maca (Lepidium meyenii)
  • Nasturtium family (Tropaeolaceae): mashua (Tropaeolum tuberosum)
  • Legume family (Fabaceae): jicama (Pachyrhizus erosus)
  • Oxalis family (Oxalidaceae): oca (Oxalis tuberosa), an Andean vegetable that is confusingly called “yam” in New Zealand

True taproots: carrot, parsnip, parsley root, salsify, burdock root, horseradish

Carrots (taproot and leaves–which make a great pesto)

Now grab a carrot, parsnip, parsley root, salsify, or burdock root for your roast vegetable medley. These are the only true taproots on our list. The roots are much longer than they are wide and taper to a point. Thin lateral roots sprout from them in random locations or in discrete vertical lines. If you cut it open and examine it in cross section you see the tough core of xylem-rich pith (water conducting tissue) in the middle surrounded by a cortical layer that separates the pith from the sweet storage tissue (parenchyma) and sugar-moving phloem that surrounds it. You have likely removed the aboveground greenery from these plants but should be able to tell or recall that it appears as if the leaves grow directly out of the crown of the taproots. They almost do. The anatomical stem on carrots and parsnips is a highly reduced disk on top of the taproot that serves as a bud-studded vascular transfer station, shuttling water and nutrients from the taproot into the leaves and flowering shoots.

Horseradish is also a taproot. A little bit grated into a sauce would make a delicious accompaniment to your roast vegetable medley. Incidentally, horseradish powder is the main ingredient in cheaper “wasabi” products available in American grocery stores, as the horseradish taste is superficially similar to that of true wasabi, which is also in the mustard family. Wasabi is also a root vegetable, but its underground storage structure is a rhizome, an underground stem, not a taproot.

Roots fused with stems (hypocotyls): celery root, beet, rutabaga, turnip, radish

celery root hypocotyls

A hypocotyl is a swollen fusion of taproot and stem base. The taproot portion is covered in fibrous secondary roots, most spectacularly in celery root. Leaf scars will be visible about these lateral roots, either surrounding the entire upper portions of the hypocotyl, as in celery root, or just at the top, as in beets and the mustard family hypocotyl vegetables (turnip, rutabaga, radish). All hypocotyl vegetables aside from beets are structurally straightforward but different from the taproots. A single layer of vascular tissue lays below the skin surface and penetrates into the storage tissue.

A rutabaga hypocotyl in the ground

Beets, however, are built from concentric rings of vascular tissue (xylem and phloem) and storage tissue (parenchyma), which is visible when the beet is cut in cross section. This ring structure is unique to the taxonomic order Caryopyllales, of which beets are a member. And as Katherine notes in her excellent beet post, the vibrant colors and earthy smell of beets are also unique. The former is due to betalain pigments, which are also unique to the Caryophyllales and distinct from the anthocyanin pigments present in all the other vegetables in our list (see our pigments post for a quick rundown of the most common pigments). The earthy smell is from a compound called geosmin. Beet is the only plant known to make it, and nobody knows why. Geosmin us usually produced by microbes in the soil and is liberated after rain to create that marvelous fresh smell after a storm.

chiogga beets show concentric vascular rings in dramatic fashion

Indidentally, our hypocotyl root vegetables here are all varieties, or subspecies, of species that also produce familiar leafy vegetables: rutabagas and the Russian or Siberian kales; turnips and Napa cabbages and mizuna; beets and Swiss chard; celery root and celery stalks or seeds. In each of these cases the variety produced for leaves has a much less pronounced hypocotyl than the variety produced as a root vegetable. Similarly, while the leaves on our hypocotyl root vegetables are all edible, they will be smaller and tougher than those on the varieties that have been bred for leaves. 

Bulbs: onion, garlic, shallots, leek

red onion bulbs growing in a planter box

Onions, shallots, garlic and other alliums might be the most famous “root vegetables” of all, but their delicious parts are constructed entirely of swollen modified leaves. The papery tunicate covering surrounding the fleshy leaf bases are also constructed out of modified leaves, all arising from the basal plate (true compressed stem) that interfaces with the spindly roots on the bottom. The fleshy part of each garlic clove is a single fat modified leaf. Inside each garlic clove or onion bulb is an apical bud that will send up new leaves and flowering shoots. Everyone who has had onions and garlic sprout on them can observe this. You can of course plant these sprouting bulbs in the soil to make a new plant. A leek is a bit intermediate between a true bulb and a big herb. They call the lower white region of overlapping succulent leaf bases a “pseudobulb,” a nod to the messy continuous nature of biology and the difficulty with labels.

slices of leek pseudobulb, showing overlapping leaf bases

Unless you’re using a variety of “sweet” onion, which has been grown or bred to lack sulfurous aromatic compounds, you might tear up when you’re cutting onions and shallots. Cutting these bulbs volatilizes the irritating compounds that otherwise protect our favorite bulbs from pests.

Root tubers: sweet potatoes, cassava

A root tuber is an enlarged root that stores starch and other nutrients. Smaller lateral roots often branch from its surface and obtain water and soil nutrients. Raw sweet potatoes are readily available candidate root tuber ingredients for your botanical scrutiny and roast vegetable medley. Cassava is not, nor should it be, at least in root tuber form. Starch derived from cassava might be elsewhere in your pantry as tapioca.

A convenient aspect of our most commonly used root vegetables is that they require very little manipulation or preparation before they can be consumed. You don’t even have to peel your sweet potatoes before you cook them. Raw cassava tubers, however, are laced full to bursting with cyanide. They are the third most important source of calories throughout the tropics, behind corn and rice, but require extensive preparation before consumption to remove the cyanide, including grating, drying, leaching and cooking.

Cassava tubers develop underground from certain roots that become fleshy storage structures. They continue to acquire water and nutrients via smaller secondary roots that dot their surface. If the plant in question grows from a seed, then the harvestable storage root may develop from the taproot that grows from the seed. This, however, proves an inefficient way to farm these species, as many more storage roots can develop on a single plant when that plant is started from a shoot—a stem with leaves. This is where the visual heuristic of placing root vegetable species on the branches of the plant tree of life gets literal with sweet potatoes and cassava. The key factor is the presence of numerous nodes—leaves along the stem and their attendant axillary buds. Cassava and sweet potato are among the plant species that can generate roots from the buds in their leaf axils under the right conditions, namely being in contact with moist soil. Roots that develop from non-root tissue (like stems) are called adventitious roots. When several nodes of a shoot are planted in the soil, many adventitious roots will develop, of which some can become enlarged storage roots. In cassava the starting shoot is a cutting from a mature cassava plant. In sweet potatoes the starting shoot is called a slip. Slips grow from buds on the proximal (closest to the parent plant) end of sweet potato tubers. On sweet potatoes this is the end with the scar where the tuber was cut away from the parent plant.

sweet potato developing slips

Rhizomes: turmeric, ginger, galangal, lotus, arrowroot, wasabi

A rhizome is a fleshy underground stem. It grows horizontally and sprouts new plants. Stems grow upward from buds near the soil surface, and roots grow from buds on the underside of the rhizome. It is structurally similar to stem tubers, like potatoes (see below), but it only grows horizontally, not in any direction, like a tuber. Rhubarb, asparagus, and irises also spread by rhizomes. If you decide to get out ginger or turmeric to flavor your vegetable medley, you’ll notice structural similarities to stem tubers, including nodes with buds.

Stem tubers: potato, sunchoke, jicama, yam

The eyes may or may not be the window into the soul, but they are our most conspicuous clue that potatoes are subterranean stem tubers, not roots. Katherine’s superb post on potato anatomy will walk you through this (potato) eye exam. Observe both ends of a potato. One end (the proximal end) bears the stump of the stolon (horizontal stem) that connected it to its mother plant. The other is tightly packed with small eyes that spiral out and around the potato. This is the growing (distal) end of the potato. New eyes originate at this end, so each eye is progressively older as you move toward the middle of the potato. Each eye contains a cluster of buds subtended by a semicircular leaf scar. The leaf in question was vestigial, translucent, and a remnant of it may still be present on your potato. Eyes are most easily visible on the “waxy” potato varieties (like Yukon Golds), which have less starch overall and a different ratio of types of starch than the “starchy” varieties (like Russets)–see Katherine’s post on potato starchiness for details.

potato eyes in spiral arrangement

The buds in each eye are axillary buds, structurally the same as Brussels sprouts. If your potato is exposed to enough light or warmth, the axillary buds will grow into new leafy stems, each of which can create a new potato plant. In this case your potato might also start synthesizing chlorophyll, turning it green. It will make toxic compounds at the same time, though, so if your potato is green you should either liberally peel it or wait to plant it in the spring.

Brussels sprouts on the stalk with residual leaf petioles. Brussels sprouts are spectacular axillary buds.

Nodes and buds are also easily visible on sunchokes, less so on jicama. True yams are actually structurally intermediate between rhizomes and stem tubers in that they might sprout adventitious roots. If you get your hands on an actual yam, instead of a sweet potato, you might see these.

sunchokes

Corms: taro, water chestnut (with a note on kohlrabi, which is not a corm)

A corm is yet another method by which plants have modified their stems to store starches and nutrients underground. The storage tissue is a swollen area of the stem above the roots and below the apical bud, from which leaves and flowers develop. Lateral buds on the stem produce modified leaves that produce a protective tunicate sheath around the starchy corm tissue. A thickened basal plate on the bottom interfaces with the roots and may sprout new corms (cormels). If you get canned water chestnuts or taro corms for your vegetable medley, these structures should be visible to you. Structurally, a taro corm is most similar to kohlrabi, which is what happened when plant breeders long ago took a weedy ancestral cabbage plant (Brassica oleracea) and bred for fat, bulbous stems. The leaf scars out the outside of a kohlrabi, and the nubbin of a root on the bottom, reveals that it is entirely stem.

Kohlrabi

The geophyte lifestyle

Potatoes are in the same genus (Solanum) as tomatoes (S. lycopersicum) and eggplants (S. melongena). The potato is the only one of these close relatives that hails from high in the Andes, where its underground tubers store the starches it needs to survive the harsh alpine conditions. This is a common ecological theme. Plants that create underground storage organs to withstand winter or seasons of drought are called geophytes. Even our short list of root vegetable species demonstrates that the geophyte lifestyle independently pops up all over the plant evolutionary tree, presumably in times and places where it may be adaptive. Even in just the Andes alone, potatoes are not the only domesticated geophyte crop with lowland relatives in the same genus devoid of starchy storage organs. Oca, confusingly called “yam” in New Zealand, where it was introduced in the mid-19th century, is otherwise known as Oxalis tuberosa. It makes stem tubers, like a potato. The specific epithet “tuberosa” separates it from non-geophyte species of Oxalis that are probably familiar to hikers and gardeners throughout the northern hemisphere. American health food stores sell dried maca hypocotyl (Lepidium meyenii) as a health food supplement, even though it is a staple crop throughout montane South America. Other Lepidium species are weedy little mustard plants. In the summer your garden may be teeming with flowering nasturtiums (Tropaeolum majus). You’ll notice a distinct lack of a fat, starchy stem tuber. Not so with mashua (Tropaeolum tuberosum).

branched taproot on a carrot

You should be well on your way at this point to getting your root vegetable medley into the oven. Finish peeling your vegetables, if you must, and dice them into approximately equally sized chunks. Toss them with a small amount of oil and salt. Add herbs if you would like. Spread them in a single layer on a baking tray or roasting pan and roast in the oven at 375 degrees Fahrenheit until they are tender, about 40 minutes. It is helpful to turn the pieces and move them around with a metal spatula halfway through the cooking time.

I like to serve these roast vegetables with some kind of sauce, often a strained yogurt mixed with salt and herbs. This is a dish filled by design with concentrated energy to maintain life through harsh seasons. The geophyte lifestyle is periodically useful for us all.

Sage, rosemary, and chia: three gifts from the wisest genus (Salvia)

This essay is our annual contribution to the Advent Botany essay collection curated by Alastair Cullham at the University of Reading. We highlight three charismatic species in the large genus Salvia (in the mint family, Lamiaceae): rosemary, sage, and chia.

Two Christmases ago we pointed out the current fad in decorating pineapples for Christmas. This year, some of our gentle readers may come across potted rosemary bushes that are trimmed into a cone to resemble a conifer. These are pleasant and ostensibly can be kept alive after the holiday season.

A rosemary shrub trimmed into a conifer shape. Photo from Pottery Barn.

A perhaps less pleasant holiday botanical encounter may include a Christmas tree-shaped Chia Pet.

Christmas tree Chia Pet. Photo from Amazon.

As far as Chia Pets go, this one is fairly innocuous. In my view, however, its only saving grace is that the chia plant itself is a fabulous taxon (Salvia hispanica), as is the rest of its large genus, Salvia, which also happens to include rosemary (Salvia rosmarinus). Rosemary of course is much more likely to make a holiday appearance as a culinary ingredient than a decoration, lovely as it is. In the kitchen it is frequently joined with its congener Salvia officinalis, usually just called garden sage. That the genus Salvia is responsible for half the taxa in the title of a Simon & Garfunkel album (Parsley, Sage, Rosemary and Thyme), notwithstanding that Art Garfunkel looks like a Chia Pet on the cover, could provide enough taxonomic joy to justify leaving this examination of these plants here. The name “sage”, however, implies wisdom, and so like the wise men of old, I shall persevere.

Parsley, Sage, Rosemary and Thyme album cover by Simon & Garfunkel (1966)

We’ll start by addressing the taxonomic elephant in the room that might otherwise distract learned readers: rosemary was only brought into the Salvia fold in 2017. Before then it was in its own small genus: Rosmarinus. The reason Rosmarinus is now Salvia is that the speciose Salvia was found to be paraphyletic: the pre-2017 conscription of the nearly 1000 species in the genus did not include all of the descendants of their most recent common ancestor. When the relationships between all the Salvia species and their closest relatives were plotted on a single phylogenetic tree, it was obvious that Rosmarinus and a few other genera should more naturally be considered Salvia, and Salvia was revised accordingly.

Rosemary (Salvia rosmarinus)

Another taxonomic bookkeeping item is to clarify that the sages in Salvia are only distant relatives of the sagebrushes and sageworts in the genus Artemisia, which is in the sunflower family Asteraceae (please see our Artemisia essay for more information about that genus, which includes the herb tarragon). The phylogenetic relationships of the major groups in Salvia from the most recent revision (Drew et al., 2017) is shown below.

Figure 2 from Drew et al. (2017): “(A) Composite chronogram of subtribe Salviinae (which contains Salvia and related taxa) based on chloroplast DNA sequences from previous molecular phylogenetic analyses. Asterisks denote nodes with low support and/or conflicting resolution among previous analyses. Salvia nomenclature follows subgeneric clades described here, including three tentatively named clades that await proper circumscription. Calibrations based on Drew & Sytsma (2012; See supplementary figure S4) (B) Circle cladogram framed on larger chronogram with weakly supported nodes collapsed, depicting species diversity and generalized staminal types within each clade of Salvia; modified after Walker & Sytsma (2007) and Walker et al. (2015).” S. elegans (pineapple sage), S. sclarea (clary sage), and S. hispanica (chia) are in the American subgenus Calosphace. Rosemary is in its own subgenus, Rosmarinus.

The phylogenetic diagram above (from Drew et al., 2017) shows locations where the flower anther structure evolved into a lever-like mechanism that aids in bee pollination by physically moving the two stamens into contact with the bee’s back when a bee enters the flower (see illustration below from Walker, Sytsma, Treutlein, & Wink, 2004).

Figure 2 from Walker et al 2004: “Flower and pollination of Salvia pratensis (Salvia clade I). A flower without the lever mechanism activated (A). As the pollinator enters the flower (B), the pollen is deposited on the back of the pollinator. As the pollinator enters an older flower (stamens removed from sketch, but remain present in flower) pollen is transferred (C). The posterior anther thecae forming the lever can be fused or free and in the subg. Leonia, produce fertile pollen”

The lever mechanism independently evolved three times within Salvia. Each of these evolutionary events was followed by rapid and prolific speciation driven by this innovation in pollination biology (Drew et al., 2017): the advent of the lever mechanism led to the radiation of around 500 species in the subgenus Calosphace in Central and South America; around 250 species evolved soon after the advent of the lever mechanism in the Salvia officinalis clade in the Mediterranean and Western Asia; and around 100 species radiated following the lever in Far East Asia in the Salvia glutinosa clade.

Sage (Salvia officinalis) flowering on my deck this summer

The bee-pollinated Salvia flowers are distinct from those pollinated by hummingbirds, which are more elongate and often red, like the flowers of pineapple sage (S. elegans), and have either evolutionarily lost the staminal lever mechanism or never had it in the first place.

Pineapple sage (Salvia elegans)

The parsley, sage, rosemary, and thyme made famous by Simon & Garfunkel started their culinary careers in Europe. All but parsley are in the mint family (Lamiaceae; see our carrot top essay for a discussion of fun chemical relationships between the flavor compounds in the mint family and the parsley family, Apiaceae). This points to the profusion of aromatic mint family species common to the rocky shrublands covering much of Europe and western Asia (Rundel et al., 2016; Vargas, Fernández-Mazuecos, & Heleno, 2018).

Called “tomillar” in spanish, literally a field of wild thyme (Thymus vulgaris) and associated species growing in the Orusco de Tajuña hills (near Madrid. Spain). Other edible Lamiaceae can be found in this plant community, including Salvia rosmarinus, and Lavandula latifolia (a lavendar). Photo by Julia Chacón-Labella.

That broad area is one of the centers of Salvia species diversity, but the genus is globally widespread. The genus probably originated and dispersed first from African and then the Mediterranean (see the figure of Salvia distribution and putative dispersal history below from Will & Claßen-Bockhoff, 2017), but the full story of dispersal and species radiation within the genus requires more elucidation.  Numerous species of Salvia are utilized as culinary or medicinal herbs or garden ornamentals throughout its range.

Fig. 8 from Will et al. 2017: “Salvia s.l. in time and space. A: Distribution of Salvia s.l., putative migration routes and fossil sites; BLB = Bering Land Bridge; D = Dorystaechas; M= Meriandra; NALB = North Atlantic Land Bridge; P = Perovskia; R = Rosmarinus; Z = Zhumeria; white arrows indicate repeated colonization of S Africa and dispersal from the Eastern Cape to Madagascar; hatched arrows (dark grey) indicate the repeated colonization of the Canary Islands from two different mainland sources; red arrow illustrate the dispersal from East Asia to Eurasia reflected by S. glutinosa; black arrows correspond to dispersal events from the OW to America reflected by two distinct lineages; ? = route uncertain; template of the map provided by the German earth science portal (www.mygeo.info). B: Simplified phylogenetic tree; nodes discussed in the text are indicated by capital letters; colors reflect distribution areas. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)”

The phylogeny above shows the large number of American taxa in subgenera Calosphace and Audibertia. While many of these species have also been used as aromatic herbs and traditional medicines, the most famous of the American Salvias, chia, is known for its nutritious seeds (Jenks & Kim, 2013a). Chia is a name given to two species of Salvia: S. columbariae and S. hispanica. S. columbariae ranges from southern California to central Mexico, at which point the range of S. hispanica begins and extends to Guatemala. Indigenous groups throughout that range historically used both species of chia as a pre-Columbian staple food source. The Aztecs cultivated it, and 16th century Spanish codices indicate it may have been as widely utilized as maize (Cahill, 2003).

Chia nutlets (S. hispanica) and a dried sage (S. officinalis) leaf for scale

Technically, the chia “seeds” you can buy in the store (or harvest yourself) are fruits. The Salvia fruit, like those of all mint family species, is called a schizocarp. The ovary inside the flower has four chambers, called locules. Each locule matures into an independent, indehiscent nutlet. The shell (pericarp) of the nutlet is stratified into the same categories of outer fruit layers as are more familiar fleshy fruits (cuticle, epicarp, mesocarp, endocarp; see our pomegranate or apple essay for more details about fruit structure), but in the Salvia nutlet the outer fruit layers are dry and compressed and inseparable from the single seed inside the fruit (Capitani, Ixtaina, Nolasco, & Tomás, 2013). Salvia nutlets mature inside of papery fused calyces (see the photo below of sage nutlets and their cup-like persistent calyces).

Sage (Salvia officinalis) leaves and nutlets inside of papery, fused persistent calyces.

The word “chia” is derived from the Aztec language Nahuatl word for “oily,” a name bestowed because chia seeds do have a high oil content (Cahill, 2003). Chia oil is rich in the omega-3 fatty acid alpha-linolenic acid, which has contributed to its recent fame as a modern health food. High alpha-linolenic acid content may be a general feature of the genus: other Salvia species, including S. officinalis, garden sage, have been shown to have high alpha-linolenic acid content in their seeds (Ben Farhat, Chaouch -Hamada, & Landoulsi, 2015).

Chia nutlets are also known for the gooey mucilage they exude when wet. This polysaccharide matrix is used as a food binder and thickener (Google “vegan egg replacement”). The production of mucilaginous diaspores (the dispersing agent, a fruit or a seed) is called myxocarpy. As Katherine discusses in her essay on okra, the flagship mucilaginous food plant, the purpose of the mucilage is likely water retention in the arid regions where these plants tend to come from. The mucilage might also act as a glue to bind the nutlet to the soil or to a dispersing animal’s fur—or to the terracotta substrate of a Chia Pet. Myxocarpy is most common in plants with small seeds growing in dry, arid areas, like those where Salvia species have radiated (Ryding, 1992).

Sage growing in coastal California, a Mediterranean-type ecosystem

Within the mint family, myxocarpy only occurs in the subfamily Nepetoideae. The subfamily, incidentally, gets its name from the catnip genus, Nepeta. Most if not all of the familiar edible herbs from the mint family are in this subfamily. Katherine has taken advantage of myxocarpy in this clade by serving soaked black basil (Ocimum basilicum) nutlets as a basil-scented vegan “caviar.”

Cat in the catnip (Nepeta cataria)

Salvia aroma and flavor–and I think the psychoactive properties of catnip for cats and known hallucinogen Salvia divinorum–comes from the terpenoids and phenolics that comprise their essential oils. The terpenoids are synthesized and stored in special glandular trichomes on the leaf surface (Schuurink & Tissier, 2019). Trichomes are hair-like extensions of the epidermis, although the glandular trichomes full of essential oil look more like water balloons than hair. Salvia species have other types of trichomes in addition to the glandular trichomes that are indeed much more hair-like and give the leaves of some Salvia a downy or prickly appearance (Kamatou et al., 2006).

Scanning electron micrograph (SEM) of a rosemary leaf. Spherical oil-filled glandular trichomes are found amongst the branched hair-like trichomes covering the lower surface of the leaf, which has a greater profusion of hairs and glands than the upper surface. When the glands are damaged or broken the aromatic essential oil is released. Magnification: x1550 (x381 at 10cm wide). Photo from https://psmicrographs.com/sems/flowers-plants/

We discussed trichome function extensively in one of our kiwi essays. The hair-like trichomes may serve the leaf by protecting it from excess solar radiation and wind and otherwise creating a more mild microclimate at the leaf surface to help it retain water.

Rosemary

Terpenoid biosynthesis requires numerous steps in which intermediate chemical products are modified by a series of specific enzymes and other proteins. Small changes in the genes responsible for those proteins can lead to big qualitative changes in the final terpenoid mix in the essential oil of a given taxon. We mammals are adept at discerning aroma differences between chemically similar terpenoids. For example, in on our carrot top essay we discussed the case of spearmint and caraway. The respective versions of the terpenoid carvone that characterize the essential oils of those plants differ only in the physical configuration of the same chemical elements, but they smell radically differently to us.

Clary sage (S. sclarea)

The function of the essential oil in the glandular trichomes, however, is not to improve human well being. Plants synthesize those lovely terpenoids as chemical defense against insect herbivores and microbial pathogens.  When the hair-like trichomes fail to stop the intruders, the glandular trichomes will explode on contact, drenching the would-be attackers in a caustic-but-fragrant deluge.

rosemary

The pharmacopeia of terpenoid aromas present in the mint family—bring to mind the scents of sages, rosemary, lavender, peppermint, spearmint, savory, thyme, oregano, marjoram, shiso, basil—owes its evolutionary origins certainly in part at least to the various selection pressures imposed on those herbal taxa by their pests. Within even commonly grown domesticated Salvia species, essential oil constituent variation leads to dramatic differences in aroma. For example, consider the differences among rosemary, garden sage, clary sage (S. sclarea), and pineapple sage (Salvia elegans), which has a notably fruity smell. The fruitiness is due in part to the presence of the terpenoids charcteristic of citrus, which are widespread across plants.

Garden sage (Salvia officinalis)

The Roman historian and natural scientist Pliny the Elder coined the name Salvia, which is derived from the Latin salvare, meaning to heal and save, and salvus, meaning uninjured or whole. The common English name “sage” of these plants ultimately comes from this same Latin root. In Pliny the Elder’s time, the Mediterranean Salvia species were considered healing herbs, good for treating colds and a variety of ailments. Salvia feature prominently in the ethnomedicine of every region in which it is found (South Africa: (Kamatou et al., 2006); Central and South America: (Jenks & Kim, 2013b)). There is a Chinese proverb that asks “How can a man grow old who has sage in his garden?” I do not know which Salvia species would have been responsible for this proverb. There are over a hundred species of Salvia species native to China, and the Mediterranean import Salvia officinalis is grown throughout the country.

Bundle of dried sage, recently, recently, in Alaska

The health and wellness meaning of “sage” is etymologically independent from its other definition as a wise thing or wise person. This second meaning ultimately comes from the Latin sapere, to know or taste. I personally enjoy conflating these meanings, tying wisdom and well-being to the plant. I like that the Salvia officinalis that grew on a pot on my deck this summer and that will season comfort food this winter is a descendent from the plants that healer contemporaries of Pliny the Elder would have searched for amidst sun-drenched rocks in the Mediterranean hills.

Salvia in macarons at my local bakery (Fire Island) this week: blackberry-sage and rosemary-merlot.

Simon & Garfunkel close the Parsley, Sage, Rosemary and Thyme album with the song “7 O’Clock News/Silent Night,” in which they juxtapose jarring newscasts from the Nixon and Johnson era with the Christmas carol. This holiday season has felt a bit like that song to me, like concerted effort is required to prevent awful, omnipresent news from drowning out the joy and solemnity of marking the darkest time of the year. But perhaps honoring traditions always involves this element of deliberately carving out the space in which to do so. Perhaps sprinkling rosemary and sage into a holiday stew or stuffing can be a radical act, a defiant embrace of old wisdom to fortify ourselves to stand with each other and create something beautiful in the cold. Regardless, insane amounts of butter will be involved, at least at my house. And when the January 2nd resolutions to “eat better” come around, chia will be there.

References

Ben Farhat, M., Chaouch -Hamada, R., & Landoulsi, A. (2015). Oil yield and fatty acid profile of seeds of three Salvia species. A comparative study. Herba Polonica, 61(2), 14–29. doi:10.1515/hepo-2015-0012

Cahill, J. P. (2003). Ethnobotany of Chia, Salvia hispanica L. (Lamiaceae). Economic Botany, 57(4), 604–618. doi:10.1663/0013-0001(2003)057[0604:EOCSHL]2.0.CO;2

Capitani, M. I., Ixtaina, V. Y., Nolasco, S. M., & Tomás, M. C. (2013). Microstructure, chemical composition and mucilage exudation of chia ( Salvia hispanica L.) nutlets from Argentina. Journal of the Science of Food and Agriculture, 93(15), 3856–3862. doi:10.1002/jsfa.6327

Drew, B. T., González-Gallegos, J. G., Xiang, C. L., Kriebel, R., Drummond, C. P., Walker, J. B., & Sytsma, K. J. (2017). Salvia united: The greatest good for the greatest number. Taxon, 66(1), 133–145. doi:10.12705/661.7

Jenks, A. A., & Kim, S. C. (2013a). Medicinal plant complexes of Salvia subgenus Calosphace: An ethnobotanical study of new world sages. Journal of Ethnopharmacology, 146(1), 214–224. doi:10.1016/j.jep.2012.12.035

Jenks, A. A., & Kim, S. C. (2013b). Medicinal plant complexes of Salvia subgenus Calosphace: An ethnobotanical study of new world sages. Journal of Ethnopharmacology, 146(1), 214–224. doi:10.1016/j.jep.2012.12.035

Kamatou, G. P., van Zyl, R. L., van Vuuren, S. F., Viljoen, A., Figueiredo, A. C., Barroso, J. G., … Tilney, P. M. (2006). Chemical composition, leaf trichome types and biological activities of the essential oils of four related Salvia Species indigenous to Southern Africa Analysis of plant volatile using 2D gas chromatography View project Chemometrics View project. Journal of Essential Oil Research. Retrieved from https://www.researchgate.net/publication/236850867

Rundel, P. W., Arroyo, M. T. K., Cowling, R. M., Keeley, J. E., Lamont, B. B., & Vargas, P. (2016). Mediterranean Biomes: Evolution of Their Vegetation, Floras, and Climate. Annual Review of Ecology, Evolution, and Systematics, 47, 383–407. doi:10.1146/annurev-ecolsys-121415-032330

Ryding, O. (1992). Pericarp structure and phylogeny within Lamiaceae subfamily Nepetoideae tribe Ocimeae. Nordic Journal of Botany, 12(3), 273–298. doi:10.1111/j.1756-1051.1992.tb01304.x

Schuurink, R., & Tissier, A. (2019). Glandular trichomes: micro-organs with model status? The New Phytologist, nph.16283. doi:10.1111/nph.16283

Vargas, P., Fernández-Mazuecos, M., & Heleno, R. (2018). Phylogenetic evidence for a Miocene origin of Mediterranean lineages: species diversity, reproductive traits and geographical isolation. Plant Biology, 20, 157–165. doi:10.1111/plb.12626

Walker, J. B., Sytsma, K. J., Treutlein, J., & Wink, M. (2004). Salvia (Lamiaceae) is not monophyletic: implications for the systematics, radiation, and ecological specializations of Salvia and tribe Mentheae. American Journal of Botany, 91(7), 1115–1125. doi:10.3732/ajb.91.7.1115

Will, M., & Claßen-Bockhoff, R. (2017). Time to split Salvia s.l. (Lamiaceae) – New insights from Old World Salvia phylogeny. Molecular Phylogenetics and Evolution, 109, 33–58. doi:10.1016/j.ympev.2016.12.041

 

Dreaming of white cocoa, hibiscus, and a happy Gomphothere

Katherine’s search for delicious white chocolate (it exists) leads to a holiday twist on truffles. And whatever your festivities proclivities may be, we Botanists in the Kitchen wish you a very merry Hibiscus and a happy Gomphothere!

White chocolate
’Tis the season to sound the trumpets and pronounce judgment upon the holy or evil nature of traditional holiday foods. Try mentioning fruit cake or egg nog in mixed company and see what happens. If you are among this season’s many vociferous critics of recently trendy white chocolate, you’ve probably been complaining that white “chocolate” is not even chocolate (uncontroversial) and that it tastes like overly sweet vanilla-flavored gummy paste dominated by an odd powdered-milk flavor, and that it exists only to cover over pretzels or perfectly good dark chocolate or to glue peppermint flakes to candy. You might even jump on the white chocolate hot cocoa trend, which has become a social media flash point now that pumpkin spice season is finally over.

It’s true that white chocolate is not technically chocolate; it lacks the cocoa solids that give genuine chocolate its rich complex flavor borne of hundreds of aromatic compounds balanced by just a touch of sour and bitter. However, proper white chocolate is made from cocoa butter, the purified fat component of the Theobroma cacao seeds from which true dark chocolate is also made. Raw cocoa butter has its own subtle scent and creamy texture, and I thought I could use it to make a version of white chocolate more to my liking, with less sugar and no stale milk flavor.

It turns out that working with cocoa butter is tricky, but it gave me the chance to learn a lot more about the nature of this finicky fat. It also turns out that sugar and some kind of milk powder are essential ingredients in all the homemade white chocolate recipes I found, because they seem to make the fat easier to work with. My plan was to make white truffles, which would showcase homemade white chocolate as an ingredient but allow me to balance its unavoidable sweetness with another flavor.

Because it can be fun and instructive to find a culinary match within the same botanical family, I searched for a balancing flavor from the list of common edible members of the Malvaceae. Baobab? Too hard to find locally. Durian? Too risky. Linden tea? Too subtle. Okra? No. Just no. Hibiscus? Bright red and tangy and perfect. Although hibiscus and Theobroma are rarely united in cooking – and they took divergent evolutionary paths about 90 million years ago – I found that these plants work extremely well together. Unlike traditional dark rich chocolate truffles, white cocoa truffles rolled in crimson hibiscus powder melt in your mouth like cool and fluffy snowballs, followed by a refreshing sour kick. Instead of being just one more rich December indulgence, these play up the bright white clear and cold elements of the season. Even better, the most widely available culinary hibiscus flowers come from the African species Hibiscus sabdariffa, sometimes called roselle, which has its own connection to the winter holidays: it stars as the main ingredient in a spicy punch served at Christmastime in the Caribbean.

Cocoa butter
Melting and molding dark chocolate into candies is notoriously difficult because the chocolate can lose its temper and become grainy or develop white oily streaks as it cools. The trouble lies in the cocoa butter, and like many chocolate dilettantes, I became interested in cocoa butter behavior when I tried to learn how to keep my dark chocolate in temper.

Cocoa butter is the fat that Theobroma cacao stores in its seeds to fuel the growth of its seedlings. Like many of the large edible seeds we casually call nuts, cacao seeds are about half fat by weight, but their fat composition is very different from the fat found in almonds, walnuts, or even the ecologically similar Brazil nuts (Chunhieng et al., 2008). In plants and animals, all naturally occurring fat is composed almost entirely of triglycerides, which are based on a glycerol backbone with three fatty acid tails. Those fatty acids can be long or short, and straight (saturated) or kinked (unsaturated). The nature of the tails determines how the individual triglyceride molecules interact to form crystals and whether the fat will be liquid or soft or firm at room temperature (Thomas et al., 2000). Very generally, the more straight tails there are, the more closely and stably the triglyceride molecules can be packed together, and the firmer the fat will be. (Manning and Dimick have a clear description of this in the case of cocoa butter, and their paper is available open source).

Whereas milk fat includes about 400 different kinds of fatty acids (Metin & Hartel, 2012), cocoa butter is dominated by only three (Griffiths & Harwood, 1991). That simple chemical profile isn’t unusual for seeds, but the types and proportions are. Cocoa butter triglycerides mostly contain two long, straight fatty acids (palmitic and stearic) and one long kinked one (oleic), in fairly equal proportions (Griffiths & Harwood, 1991). The high percentage of stearic acid is especially unusual and contributes to the solid state of cocoa butter at room temperature, while the equal combination of these three particular fatty acids causes cocoa butter to melt quickly on our skin or in our mouth.

Another unusual property of cocoa butter is that it actually cools your mouth when it melts. A piece of chocolate on your tongue gradually warms, and at first you feel it approaching your body temperature. However, precisely at its melting point – just below body temperature – it abruptly stops getting warmer, even as it continues to remove heat from your mouth, thereby cooling it. This pause in warming is due to the high latent heat of fusion of the triglyceride molecules. Because it happens just below body temperature, you feel a cooling sensation.

Interestingly, the exact proportions of the three fatty acids varies slightly with genotype and environmental conditions during the growing season (Mustiga et al., 2019). Cocoa butter is, ultimately, food for cacao tree seedlings, and so the precise fatty acid composition of the seeds certainly reflects the species’ seed ecology. To my knowledge, the details have not yet been investigated, but I assume that the fat properties influence both seed longevity under hot tropical temperatures and the ability of seedlings to metabolize the fats as they draw on them for energy during germination. In any case, because the exact proportions of the three fatty acids determines the melting point of cocoa butter, its source and genotype will also affect its behavior in our kitchens or in a factory.

A miniature sleigh and one giant Gomphothere
Speaking of ecology, all that lovely fat and protein and carbohydrate in a cacao seed is great for humans and our chocolate habits, but it doesn’t help T. cacao as a species if at least some of their seeds don’t eventually become trees. Actually, our chocolate habits over the last few millennia have done a lot to spread cacao seeds (Zarrillo et al., 2018), but for the millions of years that cacao existed before humans spread into neotropical cacao territory, other animals must have carried away the cocoa pods.

Given the hefty size of a cacao fruit (about a pound, or 500 grams), its relatively large seeds, and its yellow-orange color, the species appears adapted for dispersal by a correspondingly large animal. But no such animal candidates coexist now with Theobroma cacao or with several other similar neotropical tree species. One long-standing hypothesis has been that tropical fruits with this suite of traits are anachronisms that coevolved with now-extinct megafauna, such as gomphotheres – relatives of American mastodons – or giant ground sloths (Guimarães et al., 2008). At least one genus of gomphothere did co-occur with cacao (Lucas et al. 2013), so it is possible that they spread the seeds, but we need more complete information about their diets to be sure.

Malvaceae: Gomphothere.001

We wish you a red hibiscus and a happy gomphothere

Merry Hibiscus

The genus I chose to balance white cocoa’s sweetness and add a bit of festive color was Hibiscus, which includes hundreds of species, but Hibiscus sabdariffa is the one used most often in herbal infusions or as natural coloring or flavor. Because of its global popularity its flowers can sometimes be bought dried and in bulk at co-ops or international markets. The petals are relatively short and so a whorl of fleshy sepals makes up most of the flower, as is obvious after they have been plumped back up by a soak in hot water.

To make the hibiscus powder truffle coating, it is necessary to grind dried flowers to the finest possible powder and sieve out any remaining gritty pieces. I pulverized about half a dozen flowers in a retired coffee grinder, but you can use a mini food processor or a spice grinder. I quickly learned to let the powder settle before opening the grinder, to avoid getting a Gomphothere-sized dose of astringent dust in my human-sized nose.

After grinding, the powder must be sifted through the finest sieve you can manage. I use a gold filter like those designed to filter coffee. It takes time and patience but this step is important for the look and the mouthfeel of the truffles. The sieve full of leftover grit makes a nice cup of tangy tea.

img_0699.jpg

Dried (bottom) and reconstituted calyces (ring of sepals) of Hibiscus sabdariffa, sometimes called roselle

Truffles
Traditional dark chocolate truffles are pretty simple to make: Simmer some cream and let it cool to the point where you might consider taking a very hot bath in it. Herbs or spices may be steeped in the cream during the simmer. Measure the volume of the hot cream in ounces and add twice as many ounces by weight of finely chopped chocolate. Stir gently to melt all the pieces and then allow the mixture (called ganache) to cool at room temperature. Overheating the chocolate initially or cooling the ganache too fast takes the chocolate out of temper. When the ganache is firm, roll it into lumpy balls, coat with cocoa powder, lick your fingers, et voilà.

It turns out that dark chocolate is much more forgiving than pure cocoa butter when it comes to truffles. The first time I tried to make white cocoa truffles, I followed my usual recipe, using chopped cocoa butter in place of dark chocolate and adding some sugar with the cream. Although I was extremely careful not to overheat the cocoa butter, my ganache separated anyway. Whereas dark chocolate contains cocoa solids that support the desired type of crystal formation in solidifying chocolate (Svanberg et al., 2011), cocoa butter does not. In my various experiments with the gentle melting of cocoa butter, I went so far as to sit for an hour on a plastic bag full of grated cocoa butter. Although it should have melted at body temperature, it never got quite soft enough. I finally got the texture right when I accepted a century of professional wisdom and introduced the dreaded milk powder as well as a lot of sugar into the recipe.

Malvaceae: cocoa truffles rolled in hibiscus powder

Cocoa truffles in hibiscus powder

Below is my current working recipe, subject to additional experimentation:

  • 3 oz food grade pure cocoa butter, chopped
  • 1/2 cup powdered sugar
  • 1 1/2 teaspoons powdered milk
  • 1/4 cup cream
  • 1/4 cup sugar
  • hibiscus powder from 5 or 6 dried hibiscus flowers

In a small food processor, pulverize the cocoa butter, powdered sugar, and powdered milk. The result should be coarse dry crumbs. Place the crumbs in a small heatproof bowl or the top of a double boiler.

Bring the cream to a simmer and dissolve the sugar in it. (For one version I steeped a couple of hibiscus flowers in the cream, which tasted good but made the truffles pink all the way through. Extra cream was needed to account for some of it clinging to the flowers.)

When the cream is the temperature of a hot bath, pour it into the cocoa butter mixture. Remember, cocoa butter melts below body temperature so the cream doesn’t have to be very hot. The crumbs will cool the cream as you stir, and you want the mixture to be just above body temperature as the centers of the crumbs are melting. Those last bits to melt will seed the mixture with the desired type of crystals and favor their formation as the mixture cools.

It will take several hours for the mixture to be firm enough to roll into balls. I usually leave it at room temperature overnight. Do not rush the process by chilling it! Fast cooling favors unstable crystals and your truffles will be grainy.

Roll the mixture into balls and roll them in the hibiscus powder.

Note that you can buy white “chocolate” chips and use them in place of dark chocolate in the usual truffle recipe described above. I tried this and it worked when I increased the chips-to-cream ratio to slightly above 2-to-1. However, do read the ingredient list because many white chocolate chips (especially those labeled “white morsels”) contain no cocoa butter at all. The Gomphotheres would not approve.

Malvaceae: hibiscus cocoa truffles

White cocoa truffles with hibiscus dust and whole dried hibiscus flowers

References and further reading

Chunhieng, T., Hafidi, A., Pioch, D., Brochier, J., & Didier, M. (2008). Detailed study of Brazil nut (Bertholletia excelsa) oil micro-compounds: phospholipids, tocopherols and sterols. Journal of the Brazilian Chemical Society, 19(7), 1374-1380.

Gouveia, J. R., de Lira Lixandrão, K. C., Tavares, L. B., Fernando, L., Henrique, P., Garcia, G. E. S., & dos Santos, D. J. (2019). Thermal Transitions of Cocoa Butter: A Novel Characterization Method by Temperature Modulation. Foods, 8(10), 449.

Griffiths, G., & Harwood, J. L. (1991). The regulation of triacylglycerol biosynthesis in cocoa (Theobroma cacao) L. Planta, 184(2), 279-284.

Guimarães Jr, P. R., Galetti, M., & Jordano, P. (2008). Seed dispersal anachronisms: rethinking the fruits extinct megafauna ate. PloS one, 3(3), e1745.

Hernandez-Gutierrez, R., & Magallon, S. (2019). The timing of Malvales evolution: Incorporating its extensive fossil record to inform about lineage diversification. Molecular phylogenetics and evolution, 140, 106606. https://doi.org/10.1016/j.ympev.2019.106606

Lucas, S. G., Yuan, W., & Min, L. (2013). The palaeobiogeography of South American gomphotheres. Journal of Palaeogeography, 2(1), 19-40.

Manning, D. M. & Dimick, P. S. (1985) “Crystal Morphology of Cocoa Butter,” Food Structure: Vol. 4 : No. 2 , Article 9. Available at: https://digitalcommons.usu.edu/foodmicrostructure/vol4/iss2/9

McGee, H. (2007). On food and cooking: the science and lore of the kitchen. Simon and Schuster.

Metin, S., & Hartel, R. W. (2012). Milk fat and cocoa butter. In Cocoa butter and related compounds (pp. 365-392). AOCS Press.

Mustiga, G. M., Morrissey, J., Stack, J. C., DuVal, A., Royaert, S., Jansen, J., … & Seguine, E. (2019). Identification of climate and genetic factors that control fat content and fatty acid composition of Theobroma cacao L. beans. Frontiers in plant science, 10, 1159.

Svanberg, L., Ahrné, L., Lorén, N., & Windhab, E. (2011). Effect of sugar, cocoa particles and lecithin on cocoa butter crystallisation in seeded and non-seeded chocolate model systems. Journal of Food Engineering, 104(1), 70-80.

Thomas, A., Matthäus, B., & Fiebig, H. J. (2000). Fats and fatty oils. Ullmann’s Encyclopedia of Industrial Chemistry, 1-84.

Zarrillo, S., Gaikwad, N., Lanaud, C. et al. (2018) The use and domestication of Theobroma cacao during the mid-Holocene in the upper Amazon. Nat Ecol Evol 2, 1879–1888 doi:10.1038/s41559-018-0697-x

Angelica: Holiday fruitcake from a sometimes toxic family

Angelica archangelica may be the most festive species in a crowded field of charismatic relatives. Just watch out for the toxic branches of the Apiaceae family tree. This essay is one of our two contributions to this year’s Advent Botany holiday essay collection.

For scientific names of plants associated with the winter holidays, I think it would be hard to beat Angelica archangelica. Commonly known just as angelica or garden angelica, A. archangelica is one of the few cultivated members among the 60-ish species of large biennial herbs in the genus. They are distributed primarily across the northern reaches of Europe, Asia, and western North America.

Angelica stalks candied and photographed by hunter-harvester-gardener Hank Shaw. Recipe on his blog

Candied angelica stalks (young stems and petioles from first-year plants) have long been prized in Western Europe as a unique confection or addition to baked goods. If your path this holiday crosses with a fruitcake studded with bright green chunks, those are unfortunately dyed pieces of candied angelica stalk. Or you may have a qualitatively different experience with angelica in the form of delicious liqueurs that include the root or fruit of the plant as an ingredient. The floral, spicy, and fresh flavor of angelica graces gins, vermouths, absinthes, aquavits, bitters, and Chartreuse, among others (Amy Stewart’s website accompaniment to her book The Drunken Botanist has some tips for growing and using angelica for the DIY mixologist). Continue reading

Closing out the International Year of Pulses with Wishes for Whirled Peas (and a tour of edible legume diversity)

The United Nations declared 2016 the International Year of Pulses. What’s a pulse? It’s the dry mature seed of a large number of species in the legume family (Fabaceae): various beans, peas, soybean, chickpeas, lentils, peanuts and other groundnuts. 2016 is days from ending, so it’s high time I get up the Fabaceae diversity post I’ve been meaning to write all year long. This rounds out our year of legume coverage, which included Katherine’s posts on bean anatomy, peanuts, and green beans

thumb_2016-06-17-10-06-32_1024

Christmas Lima beans (Phaseolus lunatus), soaking before cooking

One out of every 15 flowering plant (angiosperm) species is a legume, a member of the large plant family Fabaceae (Christenhusz and Byng 2016, LPWG 2013). Boasting around 19,500 species in 750-ish genera (LPWG 2013), the Fabaceae is the third-largest plant family in the world, trailing behind only the orchid (Orchidaceae: 27,800 species) and aster (Asteraceae: 25,040 species) families (Stevens 2016). By my count, people only use about 1% of legume species for food (my list of edible legume species is found here), but that small fraction of species is mighty. People eat and grow legumes because they are nutritional superstars, can be found in almost all terrestrial ecosystems around the world, and uniquely contribute to soil fertility in both wild and agricultural ecosystems. Continue reading

Sugar

This is our first of two contributions to Advent Botany 2015.

Sugar plums dance, sugar cookies disappear from Santa’s plate, and candied fruit cake gets passed around and around. Crystals of sugar twinkle in the Christmas lights, like scintillas of sunshine on the darkest day of the year. Katherine and Jeanne explore the many plant sources of sugar.

Even at a chemical level, there is something magical and awe-inspiring about sugar. Plants – those silent, gentle creatures – have the power to harness air and water and the fleeting light energy of a giant fireball 93 million miles away to forge sugar, among the most versatile compounds on earth, and a fuel used by essentially all living organisms.

Sugar naturally occurs in various chemical forms, all arising from fundamental 3-carbon components made inside the cells of green photosynthetic tissue. In plant cells, these components are exported from the chloroplasts into the cytoplasm, where they are exposed to a series of enzymes that remodel them into versions of glucose and fructose (both 6-carbon monosaccharides). One molecule of glucose and one of fructose are then joined to form sucrose (a 12-carbon disaccharide). See figure 1.

Sugars: glu, fru, and sucrose

Figure 1.

Sucrose is what we generally use as table sugar, and it is the form of sugar that a plant loads into its veins and transports throughout its body to be stored or used by growing tissues. When the sucrose reaches other organs, it may be broken back down into glucose and fructose, converted to other sugars, or combined into larger storage or structural molecules, depending on its use in that particular plant part and species. Since we extract sugar from various parts and species, the kind of sugar we harvest from a plant, and how much processing is required, obviously reflects the plant’s own use of the sugar. Continue reading

Throwback Thursday Thanksgiving feast

We’ve got several posts in the pipeline – and this year we are contributing to Advent Botany – but meanwhile, we bring you posts from the past to nerd-up your kitchen as you cook. Don’t forget, nothing deflects from an awkward personal revelation or a heated political conversation like a well-placed observation about plant morphology.

We wish you a happy, healthy Thanksgiving!

Continue reading

Alliums, Brimstone Tart, and the raison d’etre of spices

If it smells like onion or garlic, it’s in the genus Allium, and it smells that way because of an ancient arms raceThose alliaceous aromas have a lot of sulfur in them, like their counterparts in the crucifers. You can combine them into a Brimstone Tart, if you can get past the tears.

The alliums

DSC09511

garlic curing

The genus Allium is one of the largest genera on the planet, boasting (probably) over 800 species (Friesen et al. 2006, Hirschegger et al. 2009, Mashayehki and Columbus 2014), with most species clustered around central Asia or western North America. Like all of the very speciose genera, Allium includes tremendous variation and internal evolutionary diversification within the genus, and 15 monophyletic (derived from a single common ancestor) subgenera within Allium are currently recognized (Friesen et al. 2006). Only a few have commonly cultivated (or wildharvested by me) species, however, shown on the phylogeny below. Continue reading

The Extreme Monocots

Coconut palms grow some of the biggest seeds on the planet (coconuts), and the tiny black specks in very good real vanilla ice cream are clumps of some of the smallest, seeds from the fruit of the vanilla orchid (the vanilla “bean”). Both palms and orchids are in the large clade of plants called monocots. About a sixth of flowering plant species are monocots, and among them are several noteworthy botanical record-holders and important food plants, all subject to biological factors pushing the size of their seeds to the extremes. Continue reading

A biologist eating for two

This is a bit tangential to our usual fare, but I think it’s fun, and you may as well. A friend of mine, Cara Bertron, edits the creative and delightful quarterly compendium Pocket Guide. I submitted this image, entitled “A biologist eating for two,” for the current issue, which is themed “secret recipes.” It’s a cladogram of the phylogenetic relationships among all the (multicellular) organisms I (knowingly) ate when I was pregnant with my now two-year-old daughter. Continue reading