Plant of the Week

Arabis laevigata range map.
Boechera laevigata range map. USDA PLANTS Database.

Boechera laevigata.
Boechera laevigata. Photo by Janet Novak.

Boechera laevigata.
Boechera laevigata. Photo by Janet Novak.

Smooth Rockcress (Boechera laevigata, formerly Arabis laevigata)

By Chris Mattrick

Smooth rockcress (Boechera laevigata) is a biennial member of the mustard family (Brassicaceae). This slender species is often found growing in circumneutral soils of deciduous woodlands, rocky slopes, and bottomlands. Due to its slender appearance, the species is often elusive; easily overlooked by the casual passerby. Several additional members of the genus Boechera resemble this species, but careful consideration of the basal leaves, stem condition, and flowers quickly separate this species from the others.

The stems are glaucous (covered with a waxy bloom) and can reach 40 to 50 centimeters in height. They are topped with a loose inflorescence of white drooping flowers that appear from April to June depending on the geographic location. The flowers have four petals that equal or slightly exceed the greenish sepals in length. Leaves can be divided into two types cauline (those occurring on the stem) and basal (those occurring at the base of the plant). The cauline leaves are narrow and lance-shaped, alternate in arrangement and clasp the stem at the base. The basal leaves are slightly broader with sparsely toothed or ruffled margins. The seedpod is long and quite slender, sometime exceeding 7 centimeters in length while only 2 millimeters in diameter.

Smooth rockcress ranges over the entire eastern and much of the central United States and Canada. Apparently common throughout much of this range it appears to reach the eastern limit of its range in western New England. It is absent from the Canadian maritime provinces, and only isolated occurrences are found in Maine and New Hampshire where it is listed as threatened and endangered respectively. In New Hampshire, the species was considered state historic until 2007, when two new populations were discovered. One of these was on the White Mountain National Forest.

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Wheel milkweed, Asclepias uncialis.
Wheel Milkweed (Asclepias uncialis)