[The Genus Arabis East of the Cascade Mts]

Holboell's Rockcress

Arabis holboellii

The photo above shows the fruit of Holboell's rockcress (variety pinetorum) as seen at Indian Rock (to the northwest of La Grande , OR) in the Wallowa-Whitman NF...........July 3, 2001. Note the spreading pedicel with minute, stiff hairs and the capsule which curves downward at the tip.

Characteristics:

Holboell's rockcress is a biennial or short-lived perennial wildflower. One to several simple (to branched above) stems arise to a height of 100 cm. The lower part of the plant is strongly haired with simple or radially branched hairs, while the herbage is smooth to uniformly hairy above. The basal leaves are typically arranged in a basal rosette of linear-oblanceolate to broad, oblanceolate-spatulate leaves which are 1-5.5 cm long and 2-7 mm wide. The blades range from entire to toothed and are typically covered with fine felt-like hairs or longer, coarse or fine hairs. The numerous stem leaves often overlap each other and are often petiolate, although the upper leaves on some varieties are clasping with heart-shaped bases. They range from lanceolate to narrowly oblanceolate in shape and 1-5 cm long and 2-7 mm wide. Their blades are typically pubescent although they may be glabrous on some varieties.

The inflorescence is a densely-flowered raceme of 20-100 white, pink or most commonly, pinkish-purple flowers. The pedicels are 5-15 mm long and either uniformly curved downwards or more commonly abruptly bent downwards at the base. The pedicels vary from glabrous to hairy. Each of the 4 sepals is glabrous to hairy and each is 2.5-5 mm long. Each of the 4 petals is 5-10 mm long. The fruits are glabrous siliques from 3-7 cm long and 1-2 mm wide.


Varieties:

Variety collinsii: Stem leaves with heart-shaped bases that often clasp the stem. Petals less than 7 mm long. Pedicels bent sharply downwards at their base. The siliques are more or less straight. Found from Washington to Alberta, Wyoming and east through he Dakotas and Manitoba to Quebec.

Variety pendulocarpa: Stem leaves lack heart-shaped bases. Found from British Columbia south to California and east to Montana and Colorado.

Variety pinetorum: Stem leaves with heart-shaped bases that often clasp the stem. Basal leaves are coarsely hairy. Pedicels uniformly curved outwards and downwards, not sharply reflexed downwards at the base. The siliques are thus spreading-drooping with the tip often incurved. Found from British Columbia south to California and east to Saskatchewan and Colorado.

Variety retrofracta: Stem leaves with heart-shaped bases that often clasp the stem. Leaves with margins rolled under, the upper ones pubescent. The basal leaves are covered in short, dense, felt-like hairs. Pedicels bent sharply downwards at their base. Petals over 7 mm long. Siliques 1.5-2 mm wide and more or less straight. Found from the Yukon and British Columbia south to California and east to Alberta (and occasionally to Quebec) and Colorado.


Habitat:

Hairy rock cress is found in forests and forest openings at all elevations.


Range:

Hairy rock cress is found from the Arctic south through much of North America to California, Arizona, and New Mexico, and as far east as the mid-Atlantic states.


Paul Slichter