Can daggers growing out from the surface of a leaf be anything but totally insane?
These are two species from the genus Solanum, of the Solanaceae, or Nightshade, family. You know, the family that brings us tobacco, deadly nightshade, mandrake, jimson weed, brugmansia, tomatoes, eggplants, and petunias, to name a few of the better known 2,600 or so species. Solanaceae are legendary for their killer or trippy alkaloids (“Solanum” = “to bring solace or comfort,” which seems a little contradictory…), and even several of the well-loved edible relatives have parts of the plant that are poisonous. These two ornamentals, though, are notable less for their chemistry and more for their morphology. Check out those prickles!:
S. marginatum, a.k.a. purple African or white-marginated nightshade, is native to northeastern tropical Africa, Ethiopia, and Eritrea. Having been cultivated in Europe since the 18th century, it has naturalized in the United States to the point of acquiring the USDA’s noxious weed status in 46 states. The one in these photos is growing at the top of Haight Street’s Buena Vista Park, which is one of San Francisco’s 50-plus hilltops, clocking in at 569 feet-tall.
It’s an intimidating shrub, this one. Not only is there an army of prickles on both the top and underside of the leaf, but also covering the woody stems, the pedicels (the smaller stalk that supports the flower) and the sepals
(which you can see in the above right photo, holding the shiny yellow berry). S. marginatum does not fuck around. And neither do botanists — notice I’ve been referring to the pokey parts as “prickles” rather than “thorns” or “spines,” which both just as easily roll off the layman tongue. Here’s the deal: Thorns are modified stems, meaning they arise from between the leaves and the
stem (the axil). Spines are modified leaves, and can either replace the entire “leaf,” such as in water-conserving cacti, or arise for the base of true leaves. Prickles, though, are outgrowths from the epidermis, or the outermost layer of cells on a plant. So those sharp “thorns” on roses or blackberries? Nope. Take a closer look — they’re prickles.
The entire inflorescence (group of individual flowers attached to the same larger stem) can have 10 to 25 separate flowers. Usually only one of these, however, is fertile; all the others are male flowers, with the female parts — the style and the stigma — present but atrophied. The waxy yellow berry is about two inches in diameter.
S. marginatum is used by people for more than an ornamental plant. Where it had spread in poorer countries, it was commonly used in the 1960s and ’70s as a clothing detergent and for washing sheep wool after it was sheared. In the mid-1970s, a West Berlin-based pharmaceutical company was studying the species in Ecuador to attempt the industrial synthesis of steroids from the alkaloid solasodine, which is found in the berries and is used in oral contraceptives and corticosteroid drugs. Though I found all this information in old, random books at the Helen Crocker Russell Library of Horticulture (northern Cali’s largest botanical library), I was unable to find any follow-up studies or results. I was curious whether or not, say, birth control pills are derived from S. marginatum.
The other featured species, Solanum pyracanthon (syn. pyracanthum), a.k.a. “porcupine tomato,” is endemic to southeastern Madagascar. It differs from S. marginatum in several ways. It has narrower leaves that are more deeply lobed, and the pubescence (hair) covering them is the exact texture of flocked wallpaper rather than the white fuzz of S. marginatum. Though the flowers are the same shape — five united petals forming a symmetrical corolla, as seen in most Solanaceae — on S. marginatum they’re white and on S. pyracanthon, purple. They’re similar in their gnarly prickle factor.
The color combination on S. pyracanthon is remarkable — muted green leaves, purple petals, yellow anthers, and fiery orange prickles. This species supposedly likes growing along roadsides in disturbed habitat. This one in the photos is an ornamental in a pot along Masonic Street near the Panhandle. I’ve yet to see it fruit.
And though these two species have now been pretty well botanically deconstructed — from epidermal outgrowths to ethnopharmacology — they still inspire fear and awe.