Boechera missouriensis (Greene) Al-Shehbaz

Missouri Rock Cress

Boechera missouriensis plant

Family - Brassicaceae

Habit - Biennial forb from taproot.

Stems - Erect, to 60cm, glabrous or sometimes sparsely pubescent, typically single from the base, sometimes branched, terete, green but becoming purple in strong sun.

Boechera missouriensis stemStem and leaf base.

Boechera missouriensis leavesLower stem leaves.

Leaves - Basal leaves in a dense rosette, usually present at flowering, 2-9 cm long, lanceolate to spatulate to lyrate, sharply toothed to pinnately divided, narrowed at the base to a short petiole, glabrous. Stem leaves alternate, to 8 cm, mostly appressed or strongly ascending, sessile, partially clasping, auriculate, toothed to entire, glabrous, linear-oblong, acute, green, with a single midrib. All stem leaves nearly equal in size.

Boechera missouriensis leaves

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

Flowers - Sepals 4, 3-5 mm long, oblong-elliptic, green, glabrous, slightly cupped at apex. Petals 4, 6-9 mm, milky white, erect to slightly spreading, glabrous, tapering to the base, truncate at the apex, distinct. Stamens 6, 4 larger and 2 smaller, erect, distinct. Filaments to 5 mm long, white, glabrous, terete. Anthers yellow, to 1.5 mm long. Ovary green, cylindric, glabrous, terete. Stigma small.

Boechera missouriensis flowerFlower close-up.

Boechera missouriensis calyxCalyx.

Fruits - Siliques 6-9 cm long, 1.7-2.0 mm wide, widely ascending to spreading horizontally or recurved at maturity, usually arched downward along upper half, strongly flattened. Seeds in 1 row in each locule, 1.6-1.9 mm long, oblong to broadly elliptic in outline, flattened, winged, the surface roughened and/or irregularly patterned, orange.

Flowering - April - June.

Habitat - Upland forests, rocky or sandy slopes, usually on acidic substrate.

Origin - Native to U.S.

Lookalikes - Boechera laevigata.

Other info. - This species can be found mainly in the southern half of Missouri. Its U.S. range is principally in Missouri and Arkansas, with disjunct populations also found in the upper Midwest, New England, and the Southeast. It is considered rare in these other areas. The plant is similar to B. laevigata but contrasts with that species in having very leafy stems, with the leaves strongly overlapping and usually borne erect or nearly appressed to the stem. A dense basal rosette of leaves is also usually present at flowering time. The white petals of the flowers are larger than in other species of Boechera in Missouri, and are typically about twice the length of the sepals.

This plant has also been known as Arabis missouriensis. A newer name is Borodinia missouriensis (Greene) P.J. Alexander & Windham.

Photographs taken in the Piney Creek Wilderness, Barry County, MO., 4-4-04 (DETenaglia); also at Silver Mines Recreation Area, Madison County, MO, 4-3-2016 (SRTurner).