Boechera laevigata (Muhl. ex Willd.) Al-Shehbaz

Smooth Rock Cress

Boechera laevigata plant

Family - Brassicaceae

Habit - Biennial forb with taproot.

Stems - Erect, to 1 m, pale green, glabrous, glaucous, branching or simple.

Boechera laevigata stemStem and clasping leaves.

Leaves - Alternate, simple. Basal leaves often withered by flowering time, 3-11 cm long, obovate to narrowly oblanceolate in outline, toothed or entire, short petiolate, sometimes pubescent. Stem leaves mostly spreading, sometimes overlapping, 3-15 cm long, narrowly lanceolate to linear in outline, sessile, clasping the stem, acute, entire or toothed, glabrous, glaucous, usually with pointed basal auricles, these completely surrounding the stem on larger leaves.

Boechera laevigata leaf1Leaf adaxial.

Boechera laevigata leavesLeaves.

Inflorescence - Terminal and axillary racemes, elongating in fruit. Pedicels glabrous, to 5 mm in flower, elongating in fruit to 2 cm, erect to spreading.

Boechera laevigata inflorescenceInflorescence.

Flowers - Sepals 4, 2.5-4.0 mm long, oblong-elliptic, light green, slightly cupped, erect, glabrous. Petals 4, 3-5 mm long, white, glabrous, tapering to the base, blunt to truncate or wavy at the apex, slightly exceeding or equaling the sepals. Stamens 6, 4 alike and 2 slightly smaller. Filaments to 5 mm long, white, glabrous, erect. Anthers yellow, 1.2 mm long. Ovary cylindric, green, glabrous, 3.4 mm long, 0.5 mm in diameter, 2-valved. Style very short, 0.1-0.2 mm long. Stigma capitate.

Boechera laevigata calyxCalyx.

Boechera laevigata flowerFlower.

Fruits - Siliques 5-10 cm long, 1.0-2.0 mm wide, widely ascending to spreading horizontally along the lower half, arched downward toward maturity, somewhat flattened. Seeds in 1 row in each locule, 1.3-1.8 mm long, oblong in outline, flattened, winged, the surface with a netlike or honeycomb-like pattern of ridges and pits, orange.

Boechera laevigata fruitsImmature fruits.

Flowering - April - June.

Habitat - Forests, streambanks, bluffs, ledges, often on calcaerous substrate.

Lookalikes - Boechera missouriensis.

Origin - Native to U.S.

Other info. - This inconspicuous but readily recognizable species is found mainly in the southern half of the state. It is also common throughout most of the eastern half of the U.S., and ranges into Canada as well. The flowers are typical for a mustard, with this particular species being distinguished by its long, narrow, clasping leaves and overall smoothness. Most parts of the plant are distinctly glaucous, with a waxy coating which can easily be rubbed off. A similar species is B. missouriensis, but that is a leafier plant which has pinnately lobed basal leaves, and is also not glaucous. These plants tend to prefer rocky areas and are colloquially known as "rock cresses" for that reason.

Boechera laevigata was formerly known as Arabis laevigata (Muhl. ex Willd.) Poir. A newer name is Borodinia laevigata (Muhl. ex Willd.) P.J. Alexander & Windham.

Photographs taken at Eagle Bluffs Conservation Area, Boone County, MO., 4-11-04 (DETenaglia); and also in Weldon Spring Conservation Area, 4-17-2014, and at Salt Lick Point, Monroe County, IL, 4-30-2018 (SRTurner).