Buy me some peanuts!

As part of our legume series, the Botanist in the Kitchen goes out to the ballgame where Katherine gives you the play-by-play on peanuts, the world’s most popular underground fruit. She breaks down peanut structure and strategy, tosses in a little history, and gives you a 106th way to eat them. Mmmmm, time to make some boiled peanuts.

Baseball is back, and so are peanuts in the shell, pitchers duels, lazy fly balls, and a meandering but analytical frame of mind. Is this batter going to bunt? Is it going to rain? What makes the guy behind me think he can judge balls and strikes from all the way up here? What does the OPS stat really tell you about a hitter? Is a peanut a nut? How does it get underground? What’s up with the shell?  A warm afternoon at a baseball game is the perfect time to look at some peanuts, and I don’t care if I never get back.

Peanuts fit baseball like an old glove fits your hand. Just as players through the ages have taken more clubhouse-friendly monikers, so Arachis hypogaea has many nicknames – peanuts, goobers, goober peas, groundnuts, etc. And fans love peanuts. Legend has it that San Francisco Giants fans leave four thousand pounds – two tons – of peanut shells behind after every home game. Over a season, that adds up to more than 160 tons of shells. (Fortunately, the Giants’ AT&T Park has a massive composting program). Shells make up only about a quarter of a peanut’s total mass, so at every game, six tons of edible peanut parts are consumed by the nearly 42 thousand fans typically in attendance. By my goobermetric calculations, that translates into more than a quarter pound and 700 Kcals of goober peas per person, not including any peanuts taken in as Cracker Jack. Consider that not everyone there is eating peanuts, and you have some fans hitting the peanuts pretty hard. Of course there are fans who are seriously, even dangerously, allergic to peanuts, and many teams now offer peanut-controlled sections for a few games per season. Personally, I like my peanuts best when they are boiled in brine and served in Georgia – just one of the ways you can get them at Turner Field in Atlanta.

Boiled peanuts at Turner Field in Atlanta

Boiled peanuts at Turner Field in Atlanta. Click to enlarge.


Peanut seeds cradled in the fruit wall (shell)

Wherever your home team might be, imagine you are sitting there in the stands on a warm lazy day asking yourself “what is a peanut?” Most “nuts” are not botanical nuts, and neither are peanuts. You will have heard that peanuts are “peas,” and that’s mostly right. Arachis hypogaea is in the legume family (Fabaceae), and its botanical fruit type is also called a legume, along with green beans, snap peas, and edamame. The shell of a peanut develops from its ovary (making it a fruit), and it contains the edible peanut seeds inside, surrounded by a reddish brown papery seed coat. So peanuts in the shell are fruits, and we open them up and eat the seeds.

In fact, peanuts are among the rare fruits that develop underground, although they flower above ground. They start as beautiful aerial flowers, shaped like those of its sweet pea cousins, and strikingly bright yellow. Bees love them and occasionally spread their pollen, although the flowers typically fertilize themselves (Leuck & Hammons,1965).

Arachis hypogaea 003

Peanut flower (Wikimedia Commons)

The really weird part comes after pollination, when the flower petals fall off and the ovary (soon-to-be-shell) starts to push itself underground. It’s not the flower stalk (pedicel) that buries the fruit; rather the base of the ovary itself elongates into a structure called the “peg” (Smith, 1950). A recent study (Chen et al. 2015) found literally hundreds of genes involved at different stages in this odd developmental move. Genes that give plants a sense of gravity are important in turning the peg down into the ground. Once there, the tip of the peg uses another few hundred genes to know that it’s dark and that the ovary should start to develop into a fruit.

Peanut stalks

Peanut “pegs,” which will become peanut fruits. By Alain Busser from Wikimedia Commons

But developing underground (“subterranean fructification”) is pretty tough on a fruit, and a peanut ovary is exposed to fungi, bacteria, nematodes, and fluctuating moisture levels, so another large set of genes goes on the defense against these pathogens (Chen et al. 2015). The shells also become very tough with thick-walled cells and fibers that support the network of veins bulging at the surface of the shell (Halliburton et al. 1975).FabaceaePeanutInShell

So to recap, those peanut shells have to be tough enough to withstand intense physical challenges yet adept enough to adjust to subtle environmental cues. Sitting low in the dirt all that time has roughed up their epidermis and left them pretty well skinned. Sounds like a catcher to me.

Before you eat those edible seeds, take a closer look at them. The reddish brown papery layer surrounding a peanut seed is its seed coat. Just like other familiar bean seeds, the peanut has two distinct halves which are its cotyledons (“seed leaves”). The cotyledons store a lot of nutrients to support a developing seedling, a role that makes them dense sources of protein and fat calories. Because many legume species use symbiotic bacteria to fix nitrogen from the air, they can afford to pack their seeds full of nitrogen-rich protein.

Looking down at a peanut seed, slightly ajar. The tuft in the center is a set of new leaves that will emerge when the seedling germinates.

Looking down at a peanut seed, slightly ajar. The tuft in the center is a set of new leaves that will emerge when the seedling germinates.

Between the cotyledons is a fascinating little structure that looks like a pale feathery mustache. That tiny tuft is the first set of leaves that appears above ground when you plant a fresh peanut.

Click to enlarge

Click to enlarge

But of course peanuts plant themselves, as described above. If you occasionally question a baseball manager’s strategy, just think about this insane move. When a flowering peanut pushes its fruits into the soil, the fruits remain tethered to the plant, and the seeds inside do not go far. They basically sit right under the parent plant, waiting for it to die, crowded by dozens and dozens of sibling seeds. Yes, it is a good spot, since those inbred seeds are genetically similar to their parents and would thrive where they did. Still, only a handful of them (at most) can occupy the family spot the following year. For a seed, that’s worse odds than a suicide squeeze. By contrast, most other plant species invest energy and cunning into dispersing their fruits and seeds as far as possible. They explode, or stick, or float, or travel through a gut. Bye bye baby. Peanuts’ odd reproductive habit is called “active geocarpy.” This strategy is rare in plants, but it seems to be associated with unstable soils, often at high altitudes, that are prone to freeze-thaw or extreme wet-dry cycles (Barker, 2005). Maybe active self-planting protects seeds from being buried too deeply or being unearthed when the ground shifts. Maybe sometimes they do roll away but stay in fair territory and colonize new ground.

Peanut seedling

My first recruit to the peanut farm team

In the US, we associate peanuts with the American South, and that’s where they are grown now. Although lots of American baseball players come from peanut country – San Francisco catcher Gerald “Buster” Posey grew up in Leesburg, not far from the famous peanut farms of Plains, GA – no major league baseball players have come from the original home of peanuts in southern Bolivia. Recent genetic work has narrowed the most likely origin of our cultivated peanuts (Arachis hypogaea) to a very small region in southern Bolivia, not far from where the borders of Bolivia, Paraguay, and Argentina come together (Bertioli et al. 2016). Peanut cultivation in that region began very early – almost as soon as people got there – and seems to have spread quickly. The Bertioli study estimates that our cultivated peanuts arose as a hybrid between two other groundnut species over 9 thousand years ago, and there is evidence of peanut cultivation in Peru not long after that, about 7800 years ago.

These days the US grows a lot of peanuts, and now we have a major goober glut that even baseball fans can’t soak up. The latest Farm Bill and other agricultural policies encouraged farmers to produce more peanuts and less cotton. We can’t eat all those peanuts, and we can’t store them all either. But peanuts are nutritional powerhouses, so an obvious solution is to give them away, and the USDA has made a deal to ship 500 metric tons of peanuts to Haiti. The heartbreaking part, as reported by the Washington Post and NPR, is that Haitian farmers have been growing peanuts themselves as part of that country’s agricultural recovery. Sending our peanuts to Haiti could undercut their efforts. (UPDATE: Sixty-one advocacy groups have submitted a letter opposing the peanut shipment plan. You can read their arguments here.) Meanwhile, here at home, conditions continue to favor peanut production in spite of the oversupply.

Perhaps the most prominent promotor of peanut production was George Washington Carver, the long-time faculty chair of the Agriculture Department at the Tuskegee Institute in Alabama. He saw peanuts as a crop that could replace cotton and actually start to heal some of the damage cotton had brought to both soil and souls in the South. As part of his effort, Carver  published a booklet of 105 peanut recipes, including both savory and sweet preparations, and yet he somehow failed to mention peanut brittle or boiled peanuts.

Now, if you live in the south you can easily buy canned (meh) or roadside (mmm) boiled peanuts. But if you want something really good, here’s my pitch for making your own boiled peanuts.

Boiled Peanuts

Peanuts must be raw and still in the shell. They may be dried (not roasted) or they may still be damp and soft (“green”). With dried peanuts, it speeds cooking to soak them overnight in water to soften them a bit.

For every pound of peanuts, use a half-gallon of water and about 1/2 cup of salt. Put everything in a pot and bring it to a boil. Continue to boil until the peanut seeds are soft, with no residual crunch to them. Green peanuts will take up to two hours while dried peanuts may take 10 or 12 hours. Be sure to keep the water level high enough to keep all of the shells surrounded by water. Allow the peanuts to cool in the brine and then refrigerate them and eat them within a week.

Be sure to save a few to germinate, like I did. (It’s a video. Click it!):


Barker, N. P. (2005). A review and survey of basicarpy, geocarpy, and amphicarpy in the African and Madagascan flora. Annals of the Missouri Botanical Garden, 445-462.

Bertioli, D. J., Cannon, S. B., Froenicke, L., Huang, G., Farmer, A. D., Cannon, E. K., … & Ren, L. (2016). The genome sequences of Arachis duranensis and Arachis ipaensis, the diploid ancestors of cultivated peanut. Nature genetics.

Carver, G.W. (1925) How to Grow the Peanut and 105 Ways of Preparing it for Human Consumption. Tuskegee Institute Press, Bulletin no. 31 (revised from original 1918)

Chen X., Yang Q., Li H., Li H., Hong Y., Pan L., Chen N., Zhu F., Chi X., Zhu W., Chen M., Liu H., Yang Z., Zhang E., Wang T., Zhong N., Wang M., Liu H., Wen S., Li X., Zhou G., Li S., Wu H., Varshney R., Liang X. and Yu S. (2015) Transcriptome-wide sequencing provides insights into geocarpy in peanut (Arachis hypogaea L.). Plant Biotechnol. J., doi: 10.1111/pbi.12487

Leuck, D. B., & Hammons, R. O. (1965). Pollen-collecting activities of bees among peanut flowers. Journal of Economic Entomology, 58(5), 1028-1030.

Halliburton, B. W., Glasser, W. G., & Byrne, J. M. (1975). An anatomical study of the pericarp of Arachis hypogaea, with special emphasis on the sclereid component. Botanical Gazette, 219-223.

Smith, B. W. (1950). Arachis hypogaea. Aerial flower and subterranean fruit. American Journal of Botany, 802-815.

Botany Lab of the Month, Easter edition

Dying Easter eggs with homemade vegetable dyes today made for some superb kitchen botany. Making the dyes is easy, fun, and offers insight into the fascinating evolution of plant pigments.

2016-03-26 11.58.08

Pigments serve a variety of roles in plants. Many pigments protect plant tissues from sunburn and pathogens and herbivores or perform other physiological functions (see review by Koes et al. 2005). Most noticeably, however, their brilliant colors attract animal pollinators to flowers and seed dispersers to fruit. Humans are also interested in plant pigments, which color and sometimes flavor our food, are potentially medicinally active, and have been used as natural dyes and paints for millennia.

red cabbage

red cabbage

Today we made green dye from parsley, two different yellow dyes from turmeric and yellow onion skin, and three different pinkish-purplish dyes, from red cabbage, red onion skin, and beets. The basic recipe for all the vegetable dyes is the same: coarsely chop the vegetables, pour boiling water over it (about 2 cups vegetables or 1 tablespoon turmeric powder per quart of water), and stir in white vinegar (about a tablespoon per quart). Alternatively, put the chopped vegetables in a saucepan, cover with the water, and bring to a boil. You can either immediately add the hard-boiled eggs to the vegetable soup and let it sit for 12-48 hours, or you can let the vegetables steep for an hour and strain the vegetable solids out before adding the eggs and letting it sit.

The green color from the parsley comes from the pigment chlorophyll, a key component of the light-harvesting function of the photosynthetic apparatus. Grinding the parsley in the blender released the chlorophyll from the chloroplasts.

The spice turmeric comes from the rhizome (underground stem) of Cucurma longa (family Zingiberaceae), native to tropical southeastern India. Much (if not all) of turmeric’s yellow-orange color (and its distinctive earthy flavor) comes from its curcuminoids, natural phenols. These are likely defensive compounds that help the plant thwart herbivores and pathogens.

color courtesy carotenes

color courtesy carotenes

Curcuminoids are not widespread among plants, unlike other yellowish pigments, most notably the hydrocarbon carotenoids (xanthophylls and carotenes, including vitamin A precursors). The yellow-orange color of the yolks inside our Easter eggs came from the xanthophylls lutein and zeaxanthin that the chickens obtained from their food, ultimately from plant sources. Xanthophylls provide sunscreen to leaves. Carotenes have photosynthetic roles, but they’re mostly known for the color they give to many plant structures. Most carotenes confer yellow or orange color, but the carotene lycopene is bright red and is a primary pigment of tomatoes, red carrots, watermelons, and papayas. Although carotenoids are common, I don’t know much about their use as a dye. The yellow color from the yellow onion skins came not from carotenoids but from oxidative byproducts of flavonoid pigments, notably quercetin.

Red onion color from anthocyanins and quercetin

Red onion color from anthocyanins and quercetin

Red cabbage and red onion get their purple color from anthocyanins, the most common purple and blue pigments found in nature. Beets, however, get their red and yellow colors from betalain pigments, which replace anthocyanins, and to some extent carotenoids, as a pigment source in most families in the botanical order Caryophyllales (see our Food Plant Tree of Life phylogeny page for details on phylogenetic placement of the Caryophyllales; and see this excellent article for the comparative biology of anthocyanins and betalains within the Caryophyllales). That may initially sound obscure, but there are a lot of food plants in the Caryophyllales, all with betalains instead of anthocyanins (See our Food Plant Tree of Life list).

Betalains turn salads with beets bright pink

Betalains turn salads with beets bright pink

Extra Credit: At some point in your primary education you may have done a chemistry lab (like this one) using red cabbage-derived anthocyanins to learn about pH, as the anthocyanins can display an impressive range of color depending on pH. The acid (vinegar) in the dye may complicate this plan, but I wonder if there is a way to take advantage of the pH-sensitivity of anthocyanin pigments in dye making.

Botany Lab of the Month, Superbowl Edition

In 2016, the International Year of Pulses, we’ll be writing a lot about pulses (dried beans and peas), and we’ll also tackle the huge and diverse legume family more broadly. This weekend Katherine kicks things off with February’s Botany Lab of the Month: beans and chickpeas for your Superbowl bean dip and hummus.

The species name of Cicer arietinum means "ram's head."

The species name of Cicer arietinum means “ram’s head.”

Beans are a bit like football: a boring and homogeneous mass of protein, unless you know where to look and what to look for. In this lab, we’ll make the smashing of beans into bean dip or hummus much more interesting by taking a close look at some whole beans before you reduce them to paste. The directions are very detailed, but this whole lab can be completed in the time it takes to explain the onside kick.

Of course, if you have only pre-mashed refried beans in your pantry, it’s too late. Then again, if you are using canned refried beans for your recipe, you are probably not living in the moment or sweating the details right now. That’s OK. Go watch the game and let us know when someone scores. Continue reading

Botany Lab of the Month (Oscars edition): potatoes

This month we introduce a new feature to the Botanist in the Kitchen: Botany Lab of the Month, where you can explore plant structures while you cook. In our inaugural edition, Katherine explains why she would like to add her nominee, Solanum tuberosum, to the list of white guys vying for Best Supporting Actor.

In one of this year’s biggest and best movies, Matt Damon was saved by a potato, and suddenly botanists everywhere had their very own action hero. It’s not like we nearly broke Twitter, but when the trailer came out, with Damon proclaiming his fearsome botany powers, my feed exploded with photos of all kinds of people from all over the world tagged #Iamabotanist. The hashtag had emerged a year earlier as a call to arms for a scrappy band of plant scientists on a mission to reclaim the name Botanist and defend dwindling patches of territory still held within university curricula. Dr. Chris Martine of Bucknell University, a plant science education hero himself, inspired the movement, and it was growing pretty steadily on its own. Then came the trailer for The Martian, with Matt Damon as Mark Watney, botanizing the shit out of impossible circumstances and lending some impressive muscle to the cause. The botanical community erupted with joyous optimism, and the hashtag campaign was unstoppable. Could The Martian make plants seem cool to a broader public? Early anecdotes suggest it’s possible, and Dr. Martine is naming a newly described plant species (a close potato relative) for Astronaut Mark Watney.

In the film, that potato – or actually box of potatoes – was among the rations sent by NASA to comfort the crew on Thanksgiving during a very long mission to Mars. After an accident, when the rest of the crew leaves him for dead, Watney has to generate calories as fast as he can. It’s a beautiful moment in the movie when he finds the potatoes. In a strange and scary world, Mark has found a box of old friends. They are the only living creatures on the planet besides Mark (and his own microbes), and they are fitting companions: earthy, comforting, resourceful, and perpetually underestimated. At this point in the movie, though, the feature he values most is their eyes. Continue reading

Winter mint

This is our second of our two contributions to Advent Botany 2015. All the essays are great!

An early image of candy canes. From Wikipedia

An early image of candy canes. From Wikipedia

The candy cane, that red- and white-striped hard candy imbued with peppermint oil, is a signature confection of the winter holidays. Peppermint has a long history of cultivation and both medicinal and culinary use. Infusions of the plant or its extract have been used for so many hundreds of years throughout Europe, North Africa and Western Asia that the early history of peppermint candies, including cane-shaped ones, is murky. Fortunately, the biology behind peppermint’s famous aroma is better known than the story of how it came to be a Christmas staple. Continue reading


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

How giant pumpkins got so big: A Q&A with Jessica Savage

Biologist Jessica Savage answers a few of our questions about her research on the physiology behind giant pumpkin size.

In October 2014, a giant pumpkin grown by Beni Meier of Switzerland tipped the scales at 1056 kilograms (2323 pounds) and set a new world record for the heaviest pumpkin ever weighed. Modern competitive pumpkin growers have been imposing very strong selection on pumpkin size for decades. Pumpkin fruit size keeps climbing, and old records are broken every year or two (Savage et al. 2015).

Beni Meier with his 2014 record-winning 2323-pound pumpkin, presumably a specimen of the Atlantic Giant variety of Cucurbita maxima. Photo from here.

Continue reading

Triple threat watermelon

Will seedless watermelons make us superhuman or turn our children into giants?  Hardly, but they do give home cooks the power to count chromosomes without a microscope.   Just a knife or a hard thunk on the sidewalk are enough to get a watermelon to spill its genetic guts.

If you were reading a Hearst Corporation newspaper in late 1937, you might have thought humanity would eventually be swallowed up by giant carnivorous plants, unwittingly unleashed by uncontrolled biotechnology.  The San Francisco Examiner reported on November 21st of that year that the discovery of an “elixir of growth,” meant that “…science may at last have a grip on the steering wheel of evolution, and be able to produce at will almost any kind of species…”  including “…a plague of man-eating ones.”  In 1937 Americans had much more important things to worry about, just as we do now.  Still, that discovery may in fact have threatened one cherished aspect of the American way of life by triggering the slow demise of late summer state fair watermelon seed spitting contests.  It doubtlessly paved the way for seedless watermelons, and in 2014 the total harvest of seedless watermelons on American farms – nearly 700 thousand tons – outweighed the seeded watermelon harvest more than 13 to 1 (USDA National Watermelon Report). A similar pattern is emerging this year.  Is there no stopping the attack of the seedless watermelons?

Image from microfilm of an actual page in the San Francisco Examiner, published Sunday November 21, 1937. Found in the Media and Microtext Center of Stanford University Libraries.

CLICK to read. Image from microfilm of an actual page in the San Francisco Examiner, published Sunday November 21, 1937. Found in the Media and Microtext Center of Stanford University Libraries.

And more important, how is it even possible to get seedless fruit from an annual plant?  From a plant whose only mode of reproduction is through those very seeds?  From a plant that cannot make suckers as bananas do and cannot be perpetuated endlessly through grafts like fruit trees and vines?   Such is the challenge posed every single year by watermelons, but thanks to the “elixir of growth” discovered by Albert Blakeslee and subsequent work by Hitoshi Kihara, one of the most prominent agricultural geneticists of the 20th century, the world has an elegant solution. Breeders continually improve the varieties available, and consumer demand keeps growing, yet seedless watermelon production methods have remained essentially unchanged for three quarters of a century. Continue reading

The new apples: an explosion of crisp pink honey sweet snow white candy crunch

What’s in a name?  An apple with an old fashioned name could taste as sweet, but it might not sell.  The most sought after branded varieties reveal what people look for in an apple: sweet and crunchy and bright white inside.  Do the fruits live up to their names?  Are Honeycrisp apples crunchier than others?  Do Arctics actually stay white?  We zoom in on the cells to find out.

Some of you will remember the era when the Superbowl halftime show repeatedly featured Up With People.  That was around the time when Granny Smiths arrived in our supermarkets and finally gave Americans a third apple, a tart and crunchy alternative to red and golden delicious.  Those were simple days.  Continue reading