Tiedemannia filiformis (Oxypolis filiformis)
Northern transplants like myself recall Queen Anne’s Lace (Daucus carota)—actually an Old World weed and the ancestral species of the modern carrot—in childhood meadow memories involving bug nets. Every time I see Water Cowbane my brain sees Queen Anne’s Lace. They are related in the Carrot Family. Water Cowbane lives in marshes and along wet shores throughout Florida and beyond. John and George enjoyed it in its full flowering glory Friday along the marshy nature trails in the PB County Solid Waste Authority “wilderness.”
Beware “bane” in a plant name (Henbane, Dogbane, Horsebane, Bugbane, Fleabane); it is a sign of poison, and Cowbanes have in fact poisoned cattle. Despite grocery store members, such as celery, and several spices and herbs, the Carrot Family often tends to be dangerously toxic, including Water Hemlock (Cicuta), Poison-Hemlock (Conium), and additional nasties.
It is unclear to what extent the toxins enter and protect the Black Swallowtail Butterfly caterpillar, which favors the Carrot Family in general, and locally this species as host plants. The caterpillar, which can disable the toxins, develops a false “snakes tongue” as its personal scarecrow. You might say it is a bird-bane.
Water Cowbane has abnormal leaves shaped like thick knitting needles. The proper term for organs with this shape is “terete.”
Now here is the punchline, so listen up: terete leaves (or similar photosynthetic terete stems) occur in many unrelated plants in marshy or boggy habitats. In other words, among plants of open sunny marshes there is convergent evolution leading to narrow cylindric leaves. I won’t bore you with a list of examples here, but some are in the notes below.
Looking beyond wetland plants, where else do you encounter terete leaves or round photosynthetic stems? In deserts, such as the African Spear Sansevieria familiar to gardeners. This makes sense, since a terete leaf (or a round photosynthetic stem) has a comparatively low surface area relative to internal tissues, thus reducing water loss and sun exposure. Another dry place is perched up epiphytically where water isperiodically hard to come by. Here too we see terete leaves, such as those on some Vanda Orchids. Salty habitats are “dry,” and our local Sea-Puslane has more or less terete leaves. Right—that all makes sense, but . . .
How could it be that plants sitting directly in water have “desert” –style terete leaves or similar stems? Back in the year the Wright Brothers flew (1903) botanist Rosina Rennert wrote a detailed monograph on precisely this topic featuring the Water Cowbanes as a “Swamp Xerophyte.” She is not by any means the only biologist to develop the idea of aquatic habitats being “dry” to plants; she just focused the spotlight brightly on today’s species.
I am not up on the relevant contemporary plant physiology, but going about my routine botanical business from time to time I run across repeated reasons explaining how marsh life can be “dry” to a plant. Most obviously a marsh can be relentlessly sunny, and it can dry out periodically, toggling from a wetland to a “desert.” Additionally, roots need oxygen to function properly, and a plant rooted in stinking no-oxygen mud may have trouble with root functions. And third, the water chemistry of some wetland settings impedes water uptake. Some wetland species vary the form of their leaves dramatically in response to different water and soil conditions. It would be interesting 109 years later to resume Rosina Rennert’s experiments doing that. I wonder what Rosina thought of Wilbur and Orville’s flying machine.
Notes: Unrelated plants with knitting needle leaves: Some Rushes (such as Juncus scirpoides), some Grasses (such as Panicum tenerum, Paspalum monostachyum), and some Sedges (Eleocharis interstincta, Cyperus articulatus, in both species the photosynthetic stem is the terete organ), some Arrowheads (Sagittaria teres), and Quillworts (Isoetes flaccida).