Boechera dentata (Raf.) Al-Shehbaz & Zarucchi

Rock Cress

Boechera dentata plant

Family - Brassicaceae

Habit - Biennial forb from a thin taproot or fibrous roots.

Stems - Spreading to weakly ascending, to 50 cm, multiple from base, occasionally branching in upper half, pubescent with 2-4 branched hairs.

Boechera dentata stemStem.

Leaves - Alternate, simple. Leaves pubescent with simple hairs on the upper surface and with mostly 3- or 4-branched hairs on the undersurface. Basal leaves to 15 cm long, obovate to oblanceolate in outline, irregularly toothed, narrowed at the base to a short or long petiole. Stem leaves 1-6 cm long, narrowly oblanceolate to nearly linear in outline, sessile, clasping the stem, with pointed auricles, sharply and irregularly toothed, nearly glabrous on upper surface, with with minutely hairy margins.

Boechera dentata leaf2Leaf abaxial.

Boechera dentata leavesBasal and stem leaves.

Inflorescence - Terminal and axillary racemes, compact in flower, much elongated in fruit, to 20 cm. Pedicels to 2 mm long in flower, pubescent with simple and branching hairs.

Boechera dentata inflorescenceInflorescence.

Flowers - Sepals 4, free, 1.5-2.5 mm long, narrowly oblong, green, sparsely pubescent. Petals 4, free, 2-3 mm long, white, glabrous. Stamens 6. Filaments to 2 mm long. Anthers yellow. Ovary longer than broad, terete, stellate-pubescent.

Boechera dentata flowersFlowers.

Fruits - Siliques strongly flattened, to 4 cm long, glabrous or stellate-pubescent, spreading, or ascending with maturity. Seeds in 1 row in each locule, 1.0-1.2 mm long, elliptic to narrowly oblong in outline, not flattened or winged, the surface roughened, orange.

Flowering - April - June.

Habitat - Bottomland and mesic forests, streambanks, bases of bluffs.

Origin - Native to U.S.

Lookalikes - Boechera canadensis and other members of the genus.

Other info. - This very inconspicuous plant is found scattered throughout most of Missouri. Its U.S. range is mostly within the Midwest, along with small parts of the Northeast and Canada. It favors rich, moist, and relatively undisturbed areas. The flowers are tiny and easily missed. Identification is not difficult when the plant is flowering. Look for the inconspicuous inflorescences and weak stems with clasping leaves.

This species has long been called Boechera shortii. Steyermark named two varieties for Missouri plants. Variety shortii has pubescent ovaries and fruit, whereas in var. phalacrocarpa (M. Hopkins) Steyerm. these structures are glabrous. Both are fairly common in the state. However, since the degree of pubescence is continuously variable and does not correlate with any other characters, these varieties are not currently formally recognized in Missouri.

The species was also formerly placed in the genus Arabis. A newer name is Borodinia dentata (Raf.) P.J. Alexander & Windham.

Photographs taken at Leawood City Park, Leawood, Kansas, 4-27-00, and in the Hercules Glade Wilderness, Mark Twain National Forest, Taney County, MO., 4-8-01 (DETenaglia); also at Young Conservation Area, 4-18-2015, and Little Lost Creek Conservation Area, Warren County, MO, 3-30-2012 (SRTurner).

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