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Published In: Leaflets of Botanical Observation and Criticism 2(10): 220–221. 1912. (Leafl. Bot. Observ. Crit.) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

Project Name Data (Last Modified On 7/9/2009)
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Project Data     (Last Modified On 8/10/2009)

 

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1. Planodes virginica (L.) Greene (Virginia rock cress)

Cardamine virginica L.

Arabis virginica (L.) Poir.

Sibara virginica (L.) Rollins

Pl. 326 i–k; Map 1377

Plants 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.

Common 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.

This 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.

This 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.

 
 
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