Annual or perennial herbs with the aspect of some species of Arabis, pubescent with forked hairs, with branched slender erect stems, entire or toothed leaves and small white or pink flowers in terminal racemes. Style very short; stigma 2-lobed. Siliques narrowly linear, the valves rounded, nerveless or finely nerved, dehiscent. Seeds in 1 row in each cell in the following species, in some European species in 2 rows; cotyledons incumbent. [Named from its resemblance to Arabis.]

About 12 species, natives of Europe, Asia and North America. Type species: Arabis Thaliana L.

Annual; introduced weed.

1.

A. Thaliana.

Perennial; indigenous.

2.

A. novae-angliae.

30 Arabidopsis Dc Schur Enum Pl Trans 55 1866 Pil 405

1. Arabidopsis Thaliàna (L.) Britton. Mouse-Ear Or Thale-Cress. Wall-Cress

Fig. 2063

Arabis Thaliana L. Sp. Pl. 665. 1753.

Sisymbrium Thalianum Gay, Ann. Sci. Nat. 7: 399. 1826.

Stenophragma Thaliana Celak. OEster. Bot. Zeitsch. 27: 177. 1877.

Annual, stem slender, erect, i'-i6' high, freely branching, more or less pubescent with short stiff hairs, especially below. Basal leaves 1' - 2' long, obtuse, oblanceolate or oblong, narrowed into a petiole, entire or slightly toothed; stem-leaves smaller, sessile, acute or acutish, often entire; pedicels very slender, spreading or ascending, 2"-4" long in fruit; flowers about 1 1/2" long; petals about twice the length of the sepals; pods narrowly linear, 4"-10" long, acute, often curved upward, glabrous.

In sandy fields and rocky places, Massacusetts and southern Ontario to Minnesota, Georgia, Missouri, Arkansas and Utah. Very common eastward. Naturalized from Europe. Native also of northern Asia. Turkey-pod. April-May.

2. Arabidopsis Nòvae-Ángliae (Rydb.) Britton. Low Or Northern Rock-Cress

Fig. 2064

Arabis petraea Hook. Fl. Bor. Am. 1: 42, in part. 1829. Not Lam.

Sisymbrium humile Wats. & Coult. in A. Gray, Man. Ed. 6, 71. 1890. Not Meyer, 1831.

Braya humilis Robinson, in Gray & Wats. Syn. Fl. 11: 141, in part. 1895.

Pilosella novae-angliae Rydb. Torreya 7: 158. 1907.

Perennial, erect, 4'-10' high, branching below, sparingly pubescent. Leaves spatulate, or oblanceolate, the lower obtuse, 1'-2' long, narrowed into a petiole, sharply dentate or rarely entire, the upper smaller, narrower, often acute; flowers white or pink, 1 1/2"-2" broad; pedicels ascending or erect, 2"-3" long in fruit; pods nearly terete, glabrous, narrowly linear, 6"-10" long, 1/2" wide; valves finely nerved; style i" long.

In rocky places, Anticosti, Willoughby Mountain, Vt., near Michipicoten Harbor, Lake Superior. July.

2 Arabidopsis N Vae Ngliae Rydb Britton Low Or Nor 406