Planodes virginicum (L.) Greene

Virginia Rock Cress

Planodes virginicum plant

Family - Brassicaceae

Stems - To +20cm tall, erect, herbaceous, from a taproot, pubescent below, less so to glabrous above, often reddish in strong sun, typically branching near the base.

Planodes virginicum stemUpper stem.

Planodes virginicum stemLower stem.

Leaves - Alternate, pinnately divided (pinnatifid) with 5-14 divisions on each side of the axis, to +4cm long, +1cm broad. Petioles and rachis pubescent. Divisions of the leaves acute, reduced basally, typically entire or with a small basal lobe, subulate to lanceolate glabrous or with one or two hairs near the apex. Leaves overwintering as a basal rosette.

Planodes virginicum leaves

Planodes virginicum winter basalsWinter basal leaves.

Inflorescence - Terminal and axillary racemes, compact in flower, quickly expanding in fruit to more than 2/3 of the total plant height. Pedicels short (1-3mm) in flower, elongating to +4mm in fruit, glabrous.

Flowers - Petals 4, white, distinct, to 3mm long, 1mm broad, rounded at the apex, glabrous. Stamens 6, erect. Filaments to -2mm long, glabrous, translucent-white. Anthers yellow, .2mm long. Ovary cylindric, green to purple, glabrous, 1-2mm long in flower, quickly expanding. Style wanting. Sepals 4, distinct, whitish-green to purplish in strong sun, erect, glabrous, to 2mm long, 1mm broad, oblong-lanceolate, subacute to blunt at the apex. Fruits to +2cm long, 2mm broad, glabrous, moderately compressed ascending, with a -1mm long beak, 2-valved, divided by a septum, with +/-15 seeds per valve.

Planodes virginicum flower

Planodes virginicum fruits

Flowering - March - May.

Habitat - Disturbed sites, waste ground, fallow fields, cultivated fields, roadsides, railroads.

Origin - Native to U.S.

Other info. - This little weedy species can be found mainly in the southern 2/3 of Missouri. The plant can be identified by its pinnately divided leaves, pubescent stems, small white flowers, and strongly flattened fruits.
A previously used synonym is Sibara virginica (L.) Rollins.

Photographs taken off College Ave., Columbia, MO., 4-1-04.


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