Category Archives: Botany Lab of the Month

The adoration of the pine nut

It’s the winter holiday season, when halls are bedecked with garlands of evergreens, sprigs of holly, and bunches of mistletoe to remind us that there is life in the darkness and love to be shared. This year, Katherine has added another symbolic plant to her own holiday list – pine nuts. They are more precious this year than ever.

I first started using pine nuts in holiday baking for the simple reason that they taste like pine and thus add a Christmas-tree note that almonds do not. A deeper significance was not on my mind. But pine nuts are so interesting botanically that I always slice some of them open to look for tiny pine embryos inside, and that triggers some nostalgia for conifer week in the botany lab I taught as a graduate student (along with the best co-TA ever). Specifically, I think about an odd conversation with one of the students, which for years was nothing but another funny story. Only now, decades later, do I understand that this student’s observations have something to teach us about the true meaning of pine nuts.

The remarkably unfiltered conversation happened after our student, while dissecting a pine nut, had experienced a double epiphany: he finally understood the details of sexual reproduction in pines, and he therein discovered a pathetically apt metaphor for his love life. I can still see the way he dropped his shoulders as dejection slid across his face. His exact words are lost after so many years, but he basically confided to us that, like a pine seed, he always invested a little too much and a little too early in the promise of love (or at least sex) which might never be fulfilled.

Lessons from pine sex

Both pines and flowering plants make seeds, however they don’t feed their embryos the same way. Pines (and other gymnosperms) pack a fat lunch in anticipation of an embryo, whereas flowering plants typically wait for successful fertilization and only then build up a food reserve for the embryo. Pines invest in an uncertain future, while flowering plants hold back and hedge their bets. Our student thought that his was a losing strategy, and that he should behave more like a flowering plant, but I’m not sure. I like to imagine that someone found his earnest vulnerability charming, and that he has found the loving partnership he was looking for. No matter what happened in his case, however, this I now know for certain: sometimes in life you have to muster the courage to invest fully, even recklessly, in hope. I think that’s a pretty good message for the short days of winter.

The full story of pine reproduction starts with the story of seeds, which is very complicated and still not fully resolved, but here it is in a nutshell. Seeds were an incredibly successful evolutionary innovation because they took a process that depended on wet soil or water pooling on bark or in sidewalk cracks and brought it inside a protective shell that remained on the parent plant and could function without free water. The ancestors of seed plants were similar to today’s ferns, in that they shed spores that germinated in moisture and grew into tiny plants that made eggs and swimming sperm. There are variations on this basic system throughout the plant kingdom, but ferns are a familiar example. In ferns, the large frondy generation is called the sporophyte (“spore plant”) because it makes spores. (Spores result from meiosis, so they contain half as many chromosomes per cell as the sporophyte does). Spores germinate and grow into flat green plants about the size of a lentil. These are called gametophytes because they make gametes (eggs and sperm). Under the right conditions, eggs and sperm meet, and the result is a new sporophyte.

A flat-topped Italian Stone Pine (Pinus pinea) on the Stanford campus
The tree in the center is a flat-topped Italian Stone Pine (Pinus pinea) on the Stanford campus

Pine trees are also sporophytes, but they hold onto their female spores, which develop into egg-producing female gametophytes* inside the seeds on the scales of their cones. The male spores are shed as pollen grains, with sperm-producing cells inside. Whereas free-swimming fern sperm cells get nowhere without a film of water between themselves and some eggs, pine sperm packaged into pollen grains can float through the air towards more distant eggs. Although non-seed plants have done well evolutionarily – mosses and ferns are especially diverse, widespread, and abundant – the seed habit has freed gymnosperms and angiosperms from some ecological constraints and has undoubtedly contributed to their success in a range of habitats.

What is a pine nut?

For all its oily goodness, botanically a pine nut is not a nut at all. It is a seed, and without its shell (the seed coat), a pine nut is essentially nothing but female gametophyte, often with a cute little embryo inside bearing tiny pine needles. Long before it gets to that point, however, the gametophyte has to do what its name calls for – it makes eggs, two of them – and it also accumulates a lot of nutrients for a potential embryo. A typical commercial pine nut is about two-thirds fat by weight and one-third protein and carbohydrates. A tree invests in making hundreds or thousands of those energy-rich structures each season, even though only some of the eggs will be fertilized. I don’t know what proportion of the ovules (immature seeds) are actually fertilized on a typical tree, but in a bag of pine nuts it is sometimes hard to find any with an embryo inside. Other times, most of the seeds I open up do contain baby pines.

Pine nuts are worth dissecting in your kitchen because they give you a rare glimpse into the evolutionary history outlined above. By contrast, you will never see the female gametophyte of a walnut, pecan, almond, hazelnut, peanut, or cashew, at least not in your kitchen. In flowering plants, the female gametophyte has evolved to be just a handful of cells, and when we eat an angiosperm seed, we are eating some combination of embryo and that special made-just-in-time tissue called the endosperm.

Conifer week in your kitchen

Just for auld lang syne, I gathered and photographed some of the materials we might have used during conifer week in botany lab so that you can follow along at home. If you have your own pine nuts, that’s even better. Epiphanies are encouraged but not required.

Commercial pine nuts are harvested from natural stands of a few large-seeded species. European pine nuts come from the Italian stone pine, Pinus pinea, which is planted as an ornamental in other Mediterranean type climates, including, fortunately, the campus of Stanford University where I teach. Squirrels are also a conspicuous part of the flora and fauna at Stanford, and they had already taken most of the seeds out of the cones that I picked up. In fact, pine nut processors usually harvest cones directly from the tree before their scales have opened up, and the cones are allowed to dry at a safe distance from seed predators. Unfortunately, the remaining seeds I found, stuck inside their cones and spurned by the squirrels, had become moldy, so all the photos here of gametophytes and embryos are from pine nuts I bought. Those were harvested in China and came from a different species, the Korean pine (Pinus koraiensis).

Seed poking out from between cone scales

For most of their development – between pollination and seed release – pine cones keep their scales tightly closed. You can usually find cones in various stages of development on a tree because the whole process can take two or three years. When seeds are mature, the scales of most species open up, and the seeds can be seen peeking out from between them. 

In pine species with small seeds, there is a prominent wing on each seed, and seeds flutter out away from the parent plant. Italian stone pines have very large seeds whose useless vestigial wings detach from the seeds easily.

The “shell” of a pine nut is nothing but a hard thick seed coat, its only protection against the outside world. This is what it means to be a gymnosperm — a naked seed. By contrast, the shells of other “nuts,” like pecans, almonds, or pistachios are part of the angiosperm fruit wall that surrounds the seeds, and their seed coats are very thin.

Most pine nuts are sold as bare gametophytes, without their seed coats. If you look at their pointed tips you can see a small opening where the pollen grains would have settled in to germinate and send out their pollen tubes. Pine gametophytes make two eggs in special chambers (archegonia), but usually the first egg to be fertilized is the only one that ultimately develops. I have never found twin embryos inside a pine nut, but it does happen. Twinning can also result when one embryo splits lengthwise early in development.

If you have any pine nuts to dissect, it’s best to use a razor blade because kitchen knife blades are a little too thick to do the job without mangling the embryo. A longitudinal section starting at the pointed tip reveals the embryo inside.

Above: row of pine gametophytes with embryos; below: embryos removed from the gametophytes

Here’s where it gets really interesting. Recall that one of the main functions of the female gametophyte, besides making the eggs, is to nourish the embryo. In other words, once the embryo starts to grow, it basically eats the gametophyte. It does this with the help of the suspensor, a column of disposable embryonic cells that push the main part of the new plant forward, into the gametophyte, so that it can absorb its nutrients. Once the embryo has established a distinct leafy end and root end, the root starts to grow back towards the suspensor and it crushes it. You can usually find the stringy dried up suspensor in the mature pine nut.

One of the things that makes pine nut embryos so adorable is the set of tiny needle leaves at their tips. When the embryo becomes a seedling, these will emerge to photosynthesize and take over the job of feeding the young plant. 

Pine nuts at Christmas

Italian stone pines (Pinus pinea) are native to the European side of the Mediterranean coast. In Italy they occur on the northern half of both sides of the peninsula and in the heel of the boot. The range continues westward along the southern coast of France and into Spain and Portugal where native stands are scattered throughout the interior (Viñas et al., 2016). Pine nuts were never domesticated and are generally not even cultivated in orchards. They are usually harvested from natural stands, as they have been for tens of thousands of years in Southern Europe. There is even evidence from a Spanish cave that Neanderthals collected and presumably ate P. pinea seeds (Finlayson et al., 2006). Modern humans kept up the practice and many traditional foods from the region feature pine nuts.

Pine nuts have a distinctive conifer flavor dominated by pinene, limonene, hexanal, camphene, and careen (McGee, 2020), and they work well in both savory and sweet dishes where they hold their own against strong herbs and spices. There is of course pesto from Genoa in the heart of pine nut country, but also Italian cakes (pinolata) and Christmas cookies (pignoli). A specialty in parts of Provence is the sweet tarte aux pignons . In Catalonia, All Saints Day (November 1) is celebrated with pine nut confections called panellets. None of these traditional recipes includes chocolate — likely because they predate its arrival into Europe — but I really like to bake with a combination of chocolate, orange, and pine nuts, especially at Christmas.

Puff pastry tart with leeks, bleu cheese, arugula, and pine nuts

Investing in pine nuts

For a pine tree, the substantial energy allocated to female gametophytes is an investment in potential offspring with no guarantee of success. For us, it can be a substantial financial investment that may be increasingly costly for people and the planet as well. Pine nuts have always been more expensive than peanuts or almonds, but their price jumped this year for a variety of reasons (Produce Report). Most pine nuts for sale in the United States come from stands of Korean pine growing in China. There, as everywhere, pine nut processing is unusually labor intensive and even dangerous, as rough heavy cones must be harvested by hand by skilled pickers who can navigate among the branches high above the ground. Seeds are then separated from the awkwardly knobby cones and the seed coats are removed from the female gametophytes. Pandemic-related safety measures and labor shortages have limited production, and the supply chain has been throttled, driving prices even higher. Meanwhile, a warming climate and a damaging insect pest have reduced yields (El Khoury et al., 2021). I’ll confess that I balked at the cost and used local pistachios in place of pine nuts in much of my baking this year.

The more I read about pine nut production the more concerned I became about worker protections and whether pine nut harvesting in natural stands could be sustained in the face of rising global demand. A conservation biologist working in Korean pine forests in Russia has written movingly about these highly diverse and fragile ecosystems, home to rare Amur tigers and other animals, and called for protections (Slaght, 2015).

Since a few western North American species produce large edible seeds, I looked for local harvesters who intentionally support both human and ecological communities. There are at least a couple of them, but neither had any product to sell this year. The future doesn’t look good for these businesses either, given the west’s megadrought and competition from lower-cost Chinese producers. Theirs is an investment against the odds and in favor of conserving an important cultural and ecological heritage.

The message of the pine nut

Besides their piney flavor and rich texture, what can we take from the precious little naked gametophytes that are now on my list of holiday plants? What message do I send to friends and colleagues along with my chocolate orange pine nut cake?

Pines have been around for about 150 million years, and conifers for twice that long (Rothwell et al., 2012, Jin et al., 2021), so their reproductive strategy can’t be that foolish. Their lineage persisted even when an asteroid slammed into our planet, causing the fifth mass extinction. If they don’t survive the Anthropocene, it won’t be because of their sex life. If anything, we should take their lesson to heart now more than ever. We can’t afford to wait until the last minute, like angiosperms do, to invest in future generations. It is time — past time, actually — to muster the courage and the will to dedicate all the resources we can to the preservation of the planet and our place in it. Otherwise, what hope do we have?

*note: Female gametophytes are more accurately called megagametophytes, and they derive from megaspores produced in megasporangia. Male gametophytes are really microgametophytes, pollen grains are microspores, and they are shed from microsporangia. In flowering plants, microsporangia are inside the anthers.

References and further reading

von Arnold, S., Clapham, D., & Abrahamsson, M. (2019). Embryology in conifers. Advances in Botanical Research, 89, 157-184.

El Khoury, Y., Noujeim, E., Bubici, G., Tarasco, E., Al Khoury, C., & Nemer, N. (2021). Potential Factors behind the Decline of Pinus pinea Nut Production in Mediterranean Pine Forests. Forests, 12(9), 1167.

Finlayson, C., Pacheco, F. G., Rodríguez-Vidal, J., Fa, D. A., López, J. M. G., Pérez, A. S., … & Sakamoto, T. (2006). Late survival of Neanderthals at the southernmost extreme of Europe. Nature, 443(7113), 850-853

Jin, W. T., Gernandt, D. S., Wehenkel, C., Xia, X. M., Wei, X. X., & Wang, X. Q. (2021). Phylogenomic and ecological analyses reveal the spatiotemporal evolution of global pines. Proceedings of the National Academy of Sciences, 118(20).

McGee, H. (2020). Nose dive: A field guide to the world’s smells. New York, NY: Penguin Press.

Meade, L. E., Plackett, A. R., & Hilton, J. (2021). Reconstructing development of the earliest seed integuments raises a new hypothesis for the evolution of ancestral seed‐bearing structures. New Phytologist, 229(3), 1782-1794.

Pine Nut prices reach record high. Produce Report. (2022, April 5). Retrieved December 15, 2021, from https://www.producereport.com/article/pine-nut-prices-reach-record-high

Rothwell, G. W., Mapes, G., Stockey, R. A., & Hilton, J. (2012). The seed cone Eathiestrobus gen. nov.: fossil evidence for a Jurassic origin of Pinaceae. American Journal of Botany, 99(4), 708-720.

Rudall, P. J. (2021). Evolution and patterning of the ovule in seed plants. Biological Reviews, 96(3), 943-960.

Slaght, J. C. (2015, October 19). Opinion | Making Pesto? Hold the Pine Nuts. The New York Times. https://www.nytimes.com/2015/10/19/opinion/making-pesto-hold-the-pine-nuts.html

Viñas, R. A., Caudullo, G., Oliveira, S., & de Rigo, D. (2016). Pinus pinea in Europe: distribution, habitat, usage and threats. European Atlas of Forest Tree Species; European Commission: Brussels, Belgium, 204.

The Botanist Stuck in the Kitchen With You (and Peas)

I am about to start an 8th week of online teaching and my county’s 11th week of sheltering in place. While the (essential and life saving) sheltering is getting really old, the academic quarter has sped by as usual, along with its relentless parade of deadlines and grading. Our current crisis may have no definite end, but the academic quarter must wrap up on time, ready or not.

Some people are reporting really vivid dreams right now, however, for me, the most noticeable side effect of working and teaching from home is that I never stop thinking about it. Like midway through a Saturday night screening of Reservoir Dogs when I was suddenly reminded of peas and the upcoming class meeting on fruit. Can I do this online? We’ll just have to see, won’t we?

Oh, and don’t be a Mr. Pink.

Apologies to Stealers Wheel, the terrific Michael Madsen, and his PSA on sheltering.

peeeees.003.jpeg

Closeup of sugar snap pea flower with tiny developing fruit.

The Botanist Stuck in the Kitchen

It’s the spring of 2020, and like millions of others, we Botanists in the Kitchen are sheltering at home, trying to help flatten the curve. In other words, we are stuck in the kitchen. However, neither of us is complaining right now. Personally, I (Katherine) feel secure in my home, and I am (for now) healthy. I have access to fresh and nutritious food (thank you small-holder farmers), and at the end of the day I can go for a long run along a lovely creek lined with trees and birds. Both are opportunities to connect with plants, and this blog has always been about helping people connect to plants that might just be sitting in their refrigerators.

Like many other educators, I have also been preparing to teach a spring quarter botany course, from my sofa, through a laptop. In rethinking what is essential to the class and what might be necessary for my students in this moment, I decided to assign a new reading. It’s a 2015 study by some Stanford colleagues who found, basically, that a walk through a natural green space reduced anxiety compared to a similar walk through an urban area. Maybe that’s not surprising, but they also investigated potential mechanisms by measuring the way people’s brain activity differed in the two situations. Their data suggest that an immersive experience in “nature” (with plants) reduces the kind of unproductive rumination that feeds anxiety. Nobody has done the same experiment comparing our anxiety levels after scrolling through social media or after carefully preparing broccoli and marveling at the fractal arrangement of its unopened flower buds. I do have a prediction, though. Under the current conditions, maybe it’s time to move into the kitchen and see what’s in the fridge.

 

P.S. If you are food-secure and financially able at this time, please consider giving to your local food bank. Everyone should have nutritious fresh food for body and mind.

Reference

Bratman, G. N., Hamilton, J. P., Hahn, K. S., Daily, G. C., & Gross, J. J. (2015). Nature experience reduces rumination and subgenual prefrontal cortex activation. Proceedings of the national academy of sciences, 112(28), 8567-8572.

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

The Chestnut Song

“The Christmas Song” tops the charts every December, but there’s lots more to know about those chestnuts roasting on an open fire. We peel back the layers in this essay, which is one of our two contributions to this year’s Advent Botany holiday collection.

I first tried chestnuts when I was a student in Paris. The holiday season was peaceful that year, as it should be, and I’ve cherished my memories of it all the more as intense protests are spreading through France, and violence has shattered a Christmas market in Strasbourg. In that long-ago December, though, my most consuming emotion was a kind of double nostalgia. I missed home, and yet I wasn’t quite ready to leave that beautiful city behind. As I walked for hours and hours gathering last looks, it was thrilling to get caught up in the sudden early darkness of winter and the elaborate holiday windows of the grand old department stores. During one evening promenade, I saw a street merchant who had anchored himself in the middle of the streaming agitated crowd and was patiently tending a pan of marrons grillés, freshly roasted chestnuts. The scene was so sepia toned, so achingly 19th century, that I had to have some, just to glut my sentimentality. I bought a newspaper cone of the hot aromatic nuts and managed to peel one with my cold fingers right there on the sidewalk. Continue reading

Someone's wildly inaccuarate idea of a soybean plant. the brand name has been obscured to protect its reputation.

Botany lab/rant of the month: that’s a magic beanstalk, not a soybean

In chaotic times, there are moments when you just have to take comfort in order anywhere you can find it. Katherine reviews some basic plant growth rules and takes a major company to task for undermining botanical literacy.

Would you buy milk from a dairy whose smiling cow mascot had an udder perched on top of her head? Would it bother you to see waiving teats where her ears should be? What if the unsettling image were wrapped in a lyrical ode to ungulates and to the steadfast farmers who rise before dawn to tap into “all that mammalian goodness”? Would a Holstein hagiography be enough to distract you, or would the contrast between carefully crafted ad copy and a negligent disregard for bovine biology trip your bullshit meter?

I think about this every time I buy soy milk made by one particular giant of the non-dairy milk industry. Normally I make my own soy milk – it’s cheap and fast and delicious – but sometimes life intervenes and I have to go with convenience. At my favorite local grocer, that means buying this brand. You might think it’s the gellan gum and the “natural flavors” that offend me, but really I just can’t get over the carton.

Have you ever really thought about the magic of plants?” the carton beckons. Well, yes! Yes I have! Like me, these producers have “been rooted in plant power for over 20 years.” Wow, we have so much in common! I am invited to enjoy “all that leafy goodness” and call them “plant-based, plant biased or just plain plant-prejudiced.” No plant blindness here, right? 

Except for this, the botanical version of a cow with an udder on her head and a tail growing out of her chin:

Someone's wildly inaccuarate idea of a soybean plant. the brand name has been obscured to protect its reputation.

Someone’s wildly inaccurate idea of a soybean plant. The brand name has been obscured to protect its reputation. Click to enlarge.

Judging by the edamame pod randomly stuck onto a stem, this altered photo is supposed to represent a soy bean plant (Glycine max). The words below (“Discover the power of plants at [redacted].com”) almost promise botanical accuracy. Yet, for comparison, here is an actual soybean plant, with its trifoliate leaves and bushy growth habit:

Soybeans in Warren County, Indiana

A soybean plant growing in Indiana.

Not only is the image on the soy milk carton clearly not a soybean plant, but the chimeric little sprout violates basic patterns of plant construction. When I showed the carton to my class this spring, the students were all over it with fervor and a sharpie.

Why it matters

There are many extremely important and urgent challenges facing humans and other organisms all over the planet right now, including some negative social and ecological impacts of soy and the potential for new tariffs on U.S. soybeans to make these worse. So why direct righteous ire against the photo on a carton of soy milk? First of all, what biology teacher (or parent or anyone) wants to see inaccurate or misleading images, especially if they appear every single morning on breakfast tables across the country? Second, at the risk of overstating my case, I believe that someone made deliberate choices about both the text and the image on this carton in order to evoke health and sustainability, but that these choices actually expose indifference toward the plants, the farmers, and the natural world. Similar indifference has gotten our species into a lot of trouble. We all get things wrong, but it’s important to try not to.

How a plant body is supposed to look

The green world is full of gigantic trees and tiny floating plants and delicate vines and cacti and orchids and palms and titan arums. Even if we leave aside mosses and ferns to focus on seed plants, it’s obvious that natural selection has taken a very simple basic developmental program and pushed it in almost every conceivable morphological direction. A common set of plant growth rules accommodates the varied forms of a quarter million or more species – which is astonishing – and yet the graphic designer for this soy beverage company somehow managed to stitch together an oddly improbable plant.

Under the basic developmental program, the set of stem cells (the meristem) at the apex of a growing shoot spins off a series of appendages (e.g. leaves) at regular intervals, arranged along the stem in a regular pattern. Most often, appendages spiral around the stem or occur in opposite pairs. The resulting basic vegetative unit is a leaf (or leaf homolog such as a bract, scale, or spine), the span of stem below it (the internode), and a bud at the place where the leaf meets the stem (the axil). A shoot grows by adding these units in sequence. New leaves continue to expand and internodes continue to elongate for a little while, so leaves near the tip of a shoot tend to be smaller and closer together than they eventually will be. Buds in the axils of the appendages may themselves grow out as branches that reiterate the basic body plan. The result is a modular and potentially nested structure composed of repeated subunits.

Basic flowering plant body plan

Flowering plants (and other seed plants) are built from a series of basic vegetative units, consisting of a leaf and an associated axillary bud and the internode below it. Axillary buds may develop into branches that are similarly built of a series of vegetative units. When plants begin to flower, bracts often develop in place of leaves, and flowers emerge from buds in their axils. Note that this generic plant is not meant to represent any particular species.

When a plant starts to flower, this regular organization does not go away, even if it is modified somewhat. For example, flower clusters (inflorescences) are generally produced at branch tips and along shoot axes where leafy branches would have emerged. And while leafy branches are associated with (subtended by) leaves, inflorescences are subtended by leaf-like appendages called bracts. Inflorescences themselves might transition to a complex branching architecture that differs from the rest of the vegetative plant body, but they still produce flowers in a regular pattern. Because individual flowers are conceptually (and evolutionarily) a bit like branches, they also are usually associated with bracts (Rudall & Bateman, 2010). A notable exception is plants in the mustard family (Brassicaceae); one of the genes that tells a meristem to switch gears and make a flower also suppresses formation of a subtending bract (see summary in Krizek, 2009).

Practically, what this means is that any branch, flower, or inflorescence should be associated with a subtending leaf (or bract, scale, or spine) and that any leaf (or bract, scale, or spine) potentially has a bud, branch, inflorescence, or flower associated with it. The regularity and simplicity of this fundamental pattern of seed plant development gives you a powerful framework for interpreting plants. You no longer have to ask what kohlrabi is; the leaf arrangement gives it away. You can use a combination of clues to distinguish a single compound leaf from a branch. It’s fun.

True, the pattern is not always obvious. Leaves and bracts fall off (although they often leave evident scars), and axillary buds can be extremely small or obscured. Leaves can also be reduced to tiny scales, such as those on a potato tuber. Flowers and fruits of the chocolate tree (Theobroma cacao) appear to emerge directly from an old branch, but in fact they are associated with long-gone leaf axils. And woody plants can produce new shoots adventitiously at their bases or when they are damaged. But we were talking about soybeans, not redwoods.

A magic beanstalk

Returning to the image that set off this screed, I might be able to see it as a harmless, fanciful botanical embellishment if it weren’t for the soybean pod deliberately pasted onto the stem. Surely these plant-prejudiced people could have paused their musings on the magic of plants and simply observed an actual soybean plant. They might have noticed that soybeans have compound leaves with three leaflets and that they grow more like bushes than vines. With a good photo, the artist could have gotten this image right without knowing anything at all about how plants develop. However, the text strongly implies that the central values of the company are rooted in a genuine understanding of plant biology, so I think it’s fair to hold them to a higher standard.

Now that I’ve said my piece, it’s time to take a virtual sharpie to that carton and make it botanically correct. Here’s my version.

Making soy milk at home

Homemade soy milk has many advantages. The beans for a half gallon of soy milk cost about a quarter of what you would pay for a carton at a store. Making your own is also more sustainable: bulk dried beans are less resource-intensive to ship than packaged liquid, you can often choose the source of your beans and how they are grown (e.g. organic from the U.S.), and you can control waste from the process. For example, I mix the solids strained from the liquid milk with salt, nutritional yeast, and whatever spices are handy and pack them for lunch. To the milk, I can add vanilla or not as I like. I can throw some oats or nuts or soy lecithin into the boil if I like.

  • 1 cup dried soybeans
  • water for soaking
  • 8 cups of water
  • dash of salt
  • 1/4 cup of rolled or steel-cut oats or almonds or cashews
  • immersion blender
  • fine strainer or cloth strainer bag

Soak soybeans in a medium saucepan (1.5 qt) for at least 6 hours. If you are using steel-cut oats, almonds, or cashews, soak them too.

Bring 8 cups of water to the boil in a large stock pot. The larger the better to reduce the chance that the mixture will boil over.

Drain and rinse the soybeans and return them to the sauce pan. If you are using rolled oats, add them here.

Pour some of the boiling water over the beans to cover them by about an inch, and immediately puree them with the immersion blender. Using boiling water denatures some enzymes that can cause off flavors, and an immersion blender is much safer than a regular blender for hot liquids.

Pour the blended beans into the large stock pot with the rest of the boiling water. Turn the heat to the lowest setting possible. After about 5 or 10 mins, put a lid on the pot and let it cook for another 45 mins. Add a dash of salt about midway through.

Do not leave the pot alone until it has been simmering without trouble for a while. The mixture has a tendency to boil over and make a huge mess within the first 5-10 mins.

Allow the mixture to cool for an hour or so and strain it. Refrigerate the milk right away.

The remaining solids can be flavored and eaten as they are, stirred into breakfast oatmeal or grits, baked into muffins, etc.

References

Krizek, B. A. (2009). Arabidopsis: flower development and patterning. eLS, 1-11.

Rudall, P. J., & Bateman, R. M. (2010). Defining the limits of flowers: the challenge of distinguishing between the evolutionary products of simple versus compound strobili. Philosophical Transactions of the Royal Society of London B: Biological Sciences, 365(1539), 397-409.

#Celery

It’s hard to get too excited about eating celery, but if you can manage to see a dip-drenched celery stick as a dynamically loaded cantilevered beam, then its stringy bits suddenly start to look like incredible feats of bioengineering. The mildest mannered member of the crudité platter turns out to be a misunderstood superhero.

If you are about to celebrate Thanksgiving, chances are good that you have a lot of celery in your immediate future. It shows up in dressing and cranberry relish and especially in leftovers, like turkey salad sandwiches. When I was growing up, my sister and I were tasked with picking the carcass for turkey hash, which, in our family, was basically turkey soup stretched with lots of celery and potatoes and never enough salt. Although frugal and nutritious, this one-pot crusade against food waste did not inspire a lifelong love of cooked celery. But you don’t have to like celery the food to admire its alter ego, celery the plant.

Leaves, not stems

Celery the food may not excite you, but celery the plant – the bundle of dynamically loaded cantilevered beams – is a biomechanical superhero worth exploring in the kitchen. Celery (Apium graveolens) is one of the clearest examples of how a plant’s life in the wild over tens of millions of years yielded anatomical adaptations that determine how we use it now. Because of its evolutionary responses to biomechanical challenges, it is now perfectly built to hold peanut butter or scoop dip, and when sliced, its crescent moon shapes are pretty in soup and chopped salads. On the other hand, its tough strings catch between teeth and are not easy to digest.

Celery stalks are the petioles (“stalks”) of compound leaves. They are not stems, in spite of widespread misrepresentation in elementary school lesson plans. They may look like stems to some people because they are thick and fleshy and have prominent veins running lengthwise through them. But there are several morphological clues to their leafy identity, including these: 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.

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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

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

Who wants some green bean casserole?

Is there anything good about green bean casserole? Not much beyond its association with Thanksgiving, so Katherine will be brief and just keep you company in the kitchen in case you are stuck assembling said casserole.

Since this year is the International Year of Pulses, we have been focusing on legumes, whether they count as pulses or not. Green beans do not count as pulses, but only because they are eaten as tender and fresh immature whole fruits. The very same species (Phaseolus vulgaris), when allowed to mature, could yield black beans, white beans, kidney beans, or pinto beans depending on their variety – dry seeds that are perfectly good examples of pulses.

This Thanksgiving week we are going to welcome green beans into the fold and give them a special place. It’s too bad that Thanksgiving so often presents them out of the can, overcooked, with funky flavors, and buried in a casserole. Even Wikipedia promotes this peculiar tradition : “A dish with green beans popular throughout the United States, particularly at Thanksgiving, is green bean casserole, which consists of green beans, cream of mushroom soup, and French fried onions.”

And once again, international observers ask themselves what on earth are Americans thinking? That cannot be good for them. But in the American spirit of inclusivity we invite green beans of all sorts to our tables and try to learn something from them. So if you are preparing green beans this week, take heart, take up your knives, and take a closer look.

The outside of the bean Continue reading