[Rockcresses: The Genus Arabis (and Boechera) East of the Cascade Mountains of Oregon and Washington]

Dropseed Rockcress, Holboell's Rockcress

Boechera pendulocarpa

Synonyms: Arabis exilis, Arabis holboellii, Arabis holboellii var. pendulocarpa, Boechera exilis

Inflorescence of Dropseed Rockcress, Holboell's Rockcress: Boechera pendulocarpa (Synonyms: Arabis exilis, Arabis holboellii, Arabis holboellii var. pendulocarpa, Boechera exilis)

The photo above shows Holboell's rockcress (variety pendulocarpa) as seen at Steamboat Rock State Park, Washington State..........May 2, 1998.

Lower stem leaves of Dropseed Rockcress, Holboell's Rockcress: Boechera pendulocarpa (Synonyms: Arabis exilis, Arabis holboellii, Arabis holboellii var. pendulocarpa, Boechera exilis)The photo at right shows the leaves and stems of (variety pendulocarpa) as seen at Steamboat Rock State Park, Washington State..........May 2, 1998. The stem leaves do not have heart-shaped clasping bases. Instead, they taper gradually to the stem.

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.

Variety pendulocarpa has lower, simple stems up to 25 cm high. The stems are coarsely pubescent below and more glabrous above. The basal leaves are less than 3 mm wide with entire margins. The stem leaves do not have heart-shaped, clasping bases but instead have gradually tapered bases. The pedicels are sharply reflexed downwards.


Former Varieties of Arabis holboellii:

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:

Holboell's rockcress may be found on moderately dry ground amongst sagebrush or under ponderosa pines from moderate elevations to well up in the mountains.


Range:

Holboell's rockcress is found from British Columbia south to California and east to Quebec and Greenland in the north and Michigan, Nebraska and Colorado to the south.


Basal leaves of Dropseed Rockcress, Holboell's Rockcress: Boechera pendulocarpa (Synonyms: Arabis exilis, Arabis holboellii, Arabis holboellii var. pendulocarpa, Boechera exilis)
The photo above shows a close-up of the drying leaves of Holboell's rockcress (variety pendulocarpa) as seen at Steamboat Rock State Park, Washington State..........May 2, 1998. Note the toothed margins.

Pendulant fruits of Dropseed Rockcress, Holboell's Rockcress: Boechera pendulocarpa (Synonyms: Arabis exilis, Arabis holboellii, Arabis holboellii var. pendulocarpa, Boechera exilis)

The photo above shows the fruit capsules of Holboell's rockcress (variety pendulocarpa) as seen at Steamboat Rock State Park, Washington State..........May 2, 1998. Note the sharply downturned pedicels (in some cases held against the stem) and the long, thin capsules.

Paul Slichter