Arabis missouriensis Greene - Missouri Rock Cress

Arabis missouriensis plant

Family - Brassicaceae

Stems - To +/-60cm tall, erect, herbaceous, glabrous or hairy, from a taproot, typically single from the base, typically simple except in the inflorescence, terete, green but becoming purple in strong sun.

Arabis missouriensis stem

Leaves - Basal leaves in a dense rosette, lowest of the rosette leaves spatulate, petiolate (blade tissue decurrent on the petiole), with toothed (dentate-serrate) margins, glabrous. Other leaves of the rosette lyrate-pinnatifid, petiolate, glabrous. Petioles typically purplish. Leaves of the rosette to +/-8cm long. Cauline leaves sessile, partially clasping, auriculate. Auricles pointed, +/-2mm long. Leaves coarse serrate, glabrous, linear-oblong, acute, green, with a single midrib, +/-4cm long, 7-8mm broad. All cauline leaves sub-equal in size.

Arabis missouriensis leaves

Inflorescence - Terminal and axillary racemes to +/-15cm long (tall). Axis glabrous. Pedicels 3-9mm long in flower, elongating slightly in fruit to 1.5cm long, expanded at the apex, glabrous, terete.

Flowers - Petals 4, white, erect to slightly spreading, to 9mm long, 2mm broad, glabrous, tapering to the base, truncate at the apex, distinct. Stamens 6, 4 larger and 2 smaller, erect, distinct. Filaments to 5mm long, white, glabrous, terete. Anthers yellow, to 1.5mm long, sagittate. Ovary green, cylindric, 5mm long, .7mm in diameter, glabrous, terete. Style wanting. Stigma small. Sepals 4, erect, green, glabrous, slightly more pale at the base, lanceolate, acute, entire, 5-6mm long, 2mm broad, slightly cupped at the apex, with very thin or no scarious margins, distinct. Fruits terete to slightly compressed, many seeded, glabrous, falcate.

Arabis missouriensis flowerFlower close-up.

Arabis missouriensis calyxCalyx.

Flowering - April - June.

Habitat - Acid soils of rocky wooded slopes, ridges, sand hills.

Origin - Native to U.S.

Other info. - This species can be found mainly in the most southern counties of Missouri but can also be found in the counties of the eastern Ozark region. The plant can be glabrous (typically) or hairy and is identified by its somewhat clasping leaves, toothed leaf margins, and lyrate-pinnatifid basal rosette leaves. The white petals of the flowers are also larger than other species of Arabis in Missouri.

Photographs taken in the Piney Creek Wilderness, Barry County, MO., 4-4-04.


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