Author Archives: Jeanne L. D. Osnas

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

 

Botany lab of the month: Contrasting brassica plants in the garden

This is just a quick post about some instructive cruciferous vegetable (family Brassicaceae) anatomy and within-species diversity apparent in my garden at the moment.

Red Russian kale, rutabagas, and canola oil are all different varieties of Brassica napus. Red Russian kale and rutabagas are in my garden now, and the amplification of leaves and roots, respectively, through domestication is evident.

Red Russian kale (Brassica napus)

The rutabaga leaves are large, lobed, and somewhat grayish, like the Russian kale, but they are tougher and not as numerous as on the kale.

rutabaga plant (Brassica napus; Brassicaceae)

You’ll just have to take my word for it that there is no giant rutabaga-like root (technically a swollen hypocotyl, the fused lower stem and taproot, like a turnip, radish, or maca) straining the soil surface on the kale plant.

rutabaga

Anatomical differences amplified through domestication on otherwise vaguely similar-looking cruciferous vegetable plants is also visible on Brussels sprouts and collard greens, two different varieties of Brassica oleracea. A farmer or gardener familiar with the gestalt of the plants will easily identify a Brussels sprouts plant from afar as distinct from a collard greens plant, although the large plant and leaf size are similar.

Brussels sprouts plant (Brassica oleracea)

collard greens plant (Brassica oleracea)

Up close, though, you’ll see that the larger, more tender collard greens leaves have only a very tiny bud in their leaf axils (where the leaf joins with the stem).

Giant collard green leaves subtend very tiny axillary buds.

The developing Brussels sprouts, though, are not nearly done growing and are already much larger than the axillary buds  in any other variety of B. oleracea.

Young Brussels sprouts are really just giant axillary buds developing on the stalk.

While red Russian kale is Brassica napus, most of all the other kales are leafy varieties of Brassica oleracea, along with collard greens, Brussels sprouts, cabbage (which is the enlarged terminal bud, similar to the axillary bud), kohlrabi, broccoli, and cauliflower (read about this diversity and more about the anatomy involved in our essay The extraordinary diversity of Brassica oleracea). Last year we let one of the B. oleracea kales, a curly green winterbor variety, overwinter. Many of these brassicas retain the biennial life cylce of their weedy Mediterranean ancestor (read about it in our essay Caterpillars on my crucifers: friends or foes?), so overwintering is something for which a kale plant can prepare itself. The term biennial means that the plant’s life cycle requires two years to complete. In the first year the plant produces a profusion of leaves (the “rosette”). In the second year the plant flowers, sets seed, and dies. The leaves from the first year die over the winter. It is the job of those axillary buds to survive the winter as tightly wrapped bundles of overlapping leaves that will be familiar to Brussels sprouts fans. In the spring those leaves in the axillary buds unfurl and grow as the tiny stem that supports them elongates. This unfurling of leaves from otherwise small axillary buds was apparent this spring in our overwintering kale.

This winterbor kale stem overwintered. Above each leaf scar (from last year) new leaves are expanding on a new lateral stem from the axillary buds.

If you’d like to read even more about cruciferous vegetables in the mustard family (Brassicaceae), we have a few other longer essays that fill in some of this back story:

Thanksgiving turnips and the diversity of the genus Brassica

The most political vegetables: a whirlwind tour of the edible crucifersGreens: why we eat the leaves we do

Maca: A Valentine’s Day call for comparative biology

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

Spruce tips

It’s nearing the end of the spring spruce tip season here in southcentral Alaska.

chopped spruce tips

Continue reading

Kiwifruit 2: Why are they green?

Why are some kiwifruits green when they are ripe? Or avocados or honeydew melons? The answer involves genetic accidents, photosynthesis, hidden pigments, and the words “monkey peach.”

In our kiwifruit fuzziness essay we described how the type and density of trichomes—the hairlike projections from the fruit’s skin that create the fuzziness—in the Actinidia chinensis species complex is correlated with the habitat in China to which a particular population is adapted and the ploidy level of its genome. Only polyploid (having multiple genome copies) Actinidia chinensis occupy the harshest environments—the high, arid reaches of western China—and have the highest trichome density and the longest trichomes. And those fuzzy, resilient, polyploid kiwifruits are all green on the inside (1). They are the plant kingdom’s version of an unshaved vegan after backcountry skiing for a week. The hardy plant had no trouble growing outside its plateau of origin and became the most common commercial kiwifruit in the world (A. chinensis var. deliciosa), followed closely by yellow-fleshed (“golden”), less fuzzy variants of the same species (A. chinensis var. chinensis).

An expanded view of the dozens of Actinidia species reveals orange, red, and purplish pigments that color fruits in the genus. While beautiful, this warm palette strikes me as noteworthy only in contrast to the bright green displayed by the fuzzy A. chinensis var. deliciosa that initially grabbed my attention, and, later, in green kiwiberries (A. arguta). A non-green (for lack of better terminology, “colorful”) ripe fruit, after all, is a common end point for species with fleshy fruit.

Fig. 1 from Crowhurst et al. (2008) of some fruit diversity in the kiwifruit genus Actinidia. We describe the botany and anatomy of kiwifruits in our kiwifruit fuzziness essay.

It is not difficult, however, to bring to mind other examples of species with green-ripe fruit: avocado, green grapes, some citrus, honeydew melon (I’m specifically thinking here of the pericarp or mesocarp tissue under the skin and exclude from this discussion immature fruits that lose their greenness when fully ripe, like green beans and olives). Green ripe fruit, then, in Actinidia and other taxa, seems to me to be something to explain. What, if any, function might it serve, and what are the mechanisms responsible?

While the literature on the subject is far from exhaustive, there is a fairly pedestrian explanation at least for the mechanism, if not any adaptive function, of unusually green fruit flesh outside of Actinidia: fruits start green, and straightforward mutations in a few key genes cause them to remain so. Like that intrepid, hirsute montane vegan, though, Actinidia performs the task a little differently, and it is a bit of a mystery. To understand why that is, we need some backstory on pigments in fruit and how and why they change as fruit ripens, with a focus on Actinidia. Continue reading

Kiwifruit 1: Why are they so fuzzy?

Kiwifruit is not covered in hairs. It’s covered in trichomes. And only if you’re talking about green Actinidia chinensis var. deliciosa. But, why? One answer is: pretty much to keep it from drying out. Another is: because it’s a polyploid from western China and was kind of chosen at random to be the most commonly grown kiwifruit, and they’re not all fuzzy. Those aren’t mutually exclusive answers. Put on your ecophysiology hats and grab a paring knife.

Think of fruit growth as a balancing act between ingoing and outgoing fluxes. When the balance is positive, fruits grow. When it is negative, they shrink—or shrivel. The main fluxes in question are carbon and water, which enter the fruit from the xylem and phloem of the plant vascular system. Water is lost mainly to the atmosphere via transpiration (evaporative water lost through stomata and other pores and from the skin surface). Keeping the ledger positive isn’t an easy job for a fruit. Hot, dry, and windy weather encourages transpiration and thereby increases the odds that a fruit will experience water stress. Excessive sunlight may cause sunburn. Fruits also need to avoid attack from pathogens and herbivores before the seeds within mature. A fruit’s skin—its cuticle and epidermis—is its first line of defense against abiotic and biotic threats. Some fruits resort to creative coverings to get the job done.

Here I’ll take a close look at the skin of kiwifruits. Why, exactly, are they so fuzzy?

A heart-shaped green kiwifruit (Actinidia chinensis var. deliciosa), covered in fuzzy trichomes

Continue reading

Botany Lab of the Month: Jack-O-Lantern

Happy National Pumpkin Day! Turn carving your Halloween Jack-O-Lantern into a plant dissection exercise.

IMG_7963

The first Jack-O-Lanterns were carved out of turnips in 17th-century Ireland. While the large, starchy hypocotyls (fused stem and taproot) of cruciferous vegetables are anatomically fascinating, this post will be about the stuff you are more likely cutting through to make a modern Jack-O-Lantern out of squash. Continue reading

Carrot top pesto through the looking glass

Isomers are molecules that have the same chemical constituents in different physical arrangements. Some terpenoid isomers have very different aromas and are important food seasonings. A batch of carrot top pesto led to an exploration of intriguing terpenoid isomers in the mint, carrot, and lemon families.

“Oh, c’mon. Try it,” my husband admonished me with a smile. “If anyone would be excited about doing something with them, I should think it would be you.”

The “them” in question were carrot tops, the prolific pile of lacy greens still attached to the carrots we bought at the farmer’s market. I have known for years that carrot tops are edible and have occasionally investigated recipes for them, but that was the extent of my efforts to turn them into food. My excuse is that I harbored niggling doubts that carrot tops would taste good. Edible does not, after all, imply delicious. My husband had thrown down the gauntlet, though, by challenging my integrity as a vegetable enthusiast. I took a long look at the beautiful foliage on the counter.

“Fine,” I responded, sounding, I am sure, resigned. “I’ll make a pesto with them.”

Carrot tops, it turns out, make a superb pesto. I have the passion of a convert about it, and not just because my carrot tops will forevermore meet a fate suitable to their bountiful vitality. The pesto I made combined botanical ingredients from two plant families whose flavors highlight the fascinating chemistry of structural and stereo isomers. Continue reading

Maca: A Valentine’s Day Call for Comparative Biology

Sometimes food is medicine, and sometimes that medicine is an aphrodisiac. Such is the case with Andean staple maca. What elevates this high-altitude root vegetable above its cruciferous brethren?

The ancient Greek Hippocrates, the father of modern medicine, famously said: “Let food be your medicine.” For most of human history, categorizing an edible item as either food or medicine could prove difficult or impossible (Totelin 2015). Even in the current era of modern pharmaceuticals, food and medicine exist along a continuum (Johns 1996; Etkin 2006; Valussi & Scirè 2012; Leonti 2012; Totelin 2015). The traditional Andean food Maca (Lepidium meyenii; family Brassicaceae) can be placed squarely in the middle of that continuum. Herbal medicine markets outside of its native Peru have recently discovered maca and loudly and lucratively promote an aspect of maca’s medicinal reputation that has particular relevance on Valentine’s Day: an aphrodisiac that increases stamina and fertility (Balick & Lee 2002; Wang et al. 2007). Continue reading

Botany Lab of the Month, Presidential Inauguration Edition: Saffron

If you like your spices gold-colored and expensive, find some fresh Crocus sativus flowers and grab ‘em by the…disproportionately large female reproductive organ. Small hands might work best, though it might turn your skin orange. Saffron is probably from the Middle East. If that bothers you, you may want to ban it from your spice shelves, however ill that bodes for the quality of your cabinet. After all, there is a stigma against that sort of thing.

The most expensive oversized reproductive organ in the world

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A pile of dried saffron stigmas (“threads”). Photo from Wikipedia

You may know that saffron is the most expensive spice in the world. A Spanish farmer sold his crop of high quality saffron this year for four euros per gram, which is a ninth of today’s price of gold (36 euros per gram). Saffron is expensive because its production requires a huge amount of labor and land. Saffron production is labor- and land-intensive because saffron is a botanically unique food item that defies mechanical harvest and accounts for a miniscule proportion of the plant that bears it. The saffron threads sold as spice are the dried stigmas of the flowers of the saffron crocus (Crocus sativus, family Iridaceae). Recall that the stigma is the part of the flower’s female reproductive organs that catches pollen. Pollen travels from the stigma through the style into the flower’s ovary (collectively, the stigma, style, and ovary comprise the pistil). Continue reading