1. Planodes virginica (L.) Greene (Virginia rock cress)
Cardamine virginica L.
Arabis virginica (L.)
Sibara virginica (L.)
Pl. 326 i–k; Map 1377
annual, terrestrial, mostly glabrous above, usually pubescent with mostly
unbranched hairs near the base. Stems 1 to several per plant, 10–40 cm
long, erect or ascending, sometimes branched in the upper half. Leaves
alternate and basal, the basal leaves petiolate, not clasping the stem, the
blades oblong in outline, 2–8 cm long, pinnately divided into
5–21 narrow, entire or few-toothed lobes, those of the stems similar
but gradually reduced in size and number of lobes. Inflorescences racemes, the
flowers not subtended by bracts. Sepals 1.2–1.5 mm long, narrowly
oblong-elliptic, erect, usually purple-tinged. Petals 2–3 mm long, not
lobed, white. Styles 0.2–0.5 mm long. Fruits ascending, straight,
15–25 mm long, more than 10 times as long as wide, flattened parallel
to the septum, the valves extending to the margins, the replum not winged,
dehiscing longitudinally, the valves breaking off without coiling and each with
a faint midnerve near the base. Seeds in 1 row in each locule, 1.1–1.5
mm long, broadly elliptic to nearly circular in outline, somewhat flattened,
the margins winged, the surface with a netlike or honeycomb-like pattern of
ridges and pits, reddish orange. 2n=16. March–May.
nearly throughout Missouri, except in the northernmost counties (eastern U.S. west to Kansas and Texas, also California; Mexico). Banks of streams and rivers; also moist
pastures, fallow fields, roadsides, and open, disturbed areas.
common member of the spring flora is occasionally misdetermined as Cardamine
hirsuta, C. parviflora, or C. pensylvanica, but it can be
distinguished from these species by its broader fruits with wingless replum,
fruit valves not coiled upon fruit dehiscence, and strongly winged seeds.
species has been known as Sibara virginica to most Missouri botanists
(Steyermark, 1963; Rollins, 1993), but its generic classification has long been
controversial. Ongoing, as-yet unpublished molecular systematic studies by Mark
Bielstein, a student in the Missouri Botanical Garden’s cooperative graduate
studies program with Washington University, indicate that Sibara Greene
is an unnatural genus because S. virginica forms a distinct lineage
unrelated to the other Sibara species, that this species is more closely
related to Cardamine, Nasturtium, and Rorippa, and that it should
be recognized in an independent genus, Planodes.