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

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Pirates of the Carob Bean

Maybe the name takes you back to gentler days of Moosewood Cookbook and the dusty spicy local co-op. Or maybe you were a kid back then and fell for a chocolate bait-and-switch. Whether you are sweetly nostalgic or wary and resentful, it’s worth giving carob another chance. Katherine argues that it’s time to pull this earthy crunchy 70’s food into the superfood age. She offers foraging tips and recipes to help you get to know carob on its own terms.

From November through January, the carob trees in my neighborhood dangle hard, lumpy, dark brown fruits resembling lacquered cat turds. They are delicious and nutritious and of course I collect them. I am, without apology, a pod plundering, legume looting, pirate of the carob bean. CarobPiratesIf you seek adventure and happen to live in California, Arizona, or on the Mediterranean coast, you can probably pilfer some carob fruits yourself and play with them in your kitchen. If you lack local trees or the pirate spirit, you can order carob powder and even whole carob beans with one simple click.

Although plundering season begins just as the year is ending, I always wait until January to gather carob fruits for two reasons. First, carob functions mainly as a healthful chocolate substitute, and during the holiday season, fake chocolate just seems sad. In January, however, eating locally foraged carob feels virtuous and resourceful. Second, November and December are when my local carobs make the flowers that will produce the next year’s crop, and those flowers smell like a pirate’s nether parts after a shore leave. Or so I imagine, and not without precedent. A man who should have been inured to such salty smells, Pliny the Elder, natural historian and commander in the Roman Imperial Navy, described the flowers as having “a very powerful odor.” It’s not clear why these flowers have a sort of seaman scent, since the main volatiles wafting from the flowers – linalools and farnesene – smell like lilies and gardenias (Custódio et al., 2006). In any case, I keep my distance until the flowers have finished mating season.

Carob trees

Despite their stinky flowers, carobs make great street trees and produce a valuable crop in many Mediterranean-type climates. They are beautiful, tolerant of dry and poor soils, pest resistant, and tidy. Carobs are legumes – like familiar peas and beans – but they belong to a different branch of the legume family (Caesalpinioideae), one that contains mostly trees and woody shrubs with tough inedible fruit (Legume Phylogeny Working Group, 2017). Carob pods look about as edible as Jack Sparrow’s boots, and the species’ scientific name, Ceratonia siliqua, means “horny long pod,” which well captures the intimidating nature of their leathery fruit. But as you will see below, the fruits are easy to harvest and process, and their sweet pulp is worth seeking out. Continue reading

A holiday pineapple for the table

This deep dive into pineapple anatomy is our contribution this year to the very fun Advent Botany essay collection, a celebration of plants that are at least somewhat tangentially connected to the winter holidays. In previous years we’ve contributed essays on figs, peppermint, and sugar.

December is the time to bring out the fancy Christmas china, polish the silver pitchers, and . . . bedeck your best bromeliads. In 2017, as in 1700, no proper hostess can be without a pineapple for her centerpiece. Here we unpack the botany of pineapple, which is as complicated and fabulous as its cultural history. A proper hostess, after all, should also be able to dazzle her guests with tales of tropical fruit morphology. Continue reading

#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

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

Preserving diversity with some peach-mint jam

We are knee deep in peach season, and now is the time to gather the most diverse array of peaches you can find and unite them in jam. Katherine reports on some new discoveries about the genetics behind peach diversity and argues for minting up your peach jam.

Jam inspiration

Fresh peaches at their peak are fuzzy little miracles, glorious just as they are. But their buttery mouthfeel and dripping juice are lost when peaches are processed into jam and spread across rough toast. To compensate for textural changes, cooked peaches need a bit more adornment to heighten their flavor, even if it’s only a sprinkling of sugar. Normally I am not tempted to meddle with perfection by adding ginger or lavender or other flavors to peach jam. This year, however, as I plotted my jam strategy, the unusual juxtaposition of peach and mint found its way into my imagination over and over again, like the insistent echo of radio news playing in the background. Peach and mint, peach and mint, peach and mint – almost becoming a single word. To quiet the voice in my head I had to make some peach-mint jam. The odd combination turned out to be wonderful, and I’m now ready to submit the recipe to a candid world. As we will see below, it’s not without precedent. Mmmmmmpeachmint jam. 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

Buddha’s hand citrons and a wish for peace on earth in 2017

Winter is the season for citrus fruit, and January is the month for breaking out of old routines, so stop staring at your navel and learn about one of the weirder citrus varieties.

I’ll never forget the day one of my general botany students brought to class a Buddha’s hand citron, pulled from a tree right outside our classroom. I had only recently moved to northern California from Indiana, and I’d never seen anything like it: it was a monstrous mass of a dozen pointed twisted fingers splayed irregularly from a stout base. It had the firm heft and girth of a grapefruit and the unmistakable pebbled skin of a citrus fruit, so I wondered whether my student had found a grossly deformed grapefruit; but the oil in the peel smelled heavenly and not at all like a grapefruit. In class we cut through a big finger and found no juicy segments, just white citrus pith all the way through.

Immature Buddha's hand on the tree

Immature Buddha’s hand on the tree

We eventually discovered that this fascinating fruit was a Buddha’s hand citron, Citrus medica variety sarcodactylis, meaning fleshy (sarco-) fingered (-dactyl) citron. Since that day many years ago I’ve become an unapologetic (if surreptitious) collector of the fruits from that same campus tree. The citrons do not drop from the tree on their own, yet I often find one or two lying nearby, probably torn off by a curious tourist or student and then abandoned. Obviously these fruits need a good home, and where better than the window sill in my office?

The first time I left one closed up in my office over a weekend, I opened the door on Monday morning to a waft of fruity floral aroma. It turns out that many people in China and India use the fruit to scent the air, although in west Asia and Europe the fleshy fingers are more often candied or used to flavor alcohol. I do both: the fruits make my office smell nice until they are fully yellow, and then I cook them.

It can be difficult or expensive to get your own hands on a fingered citron, but it’s easy to find a navel orange almost any time of the year. Fortunately, the patterns underlying the morphology of the fingered fruit can also be seen in an everyday navel orange. Between our photos of Buddha’s hands and your own navel orange, you should be able to follow along at home. Continue reading