Vor.. I1.] MUSTARD FAMILY. 147 
1. Arabis Virginica (L.) Trelease. Virginia Rock-cress. (Fig. 1771.) 
Cardamine Virginica 1. Sp. Pl. 656. 1753- \ B 
Cardamine Ludoviciana Hook. Journ. Bot. I: 191. 
ean Ludoviciana Meyer, Ind. Sem. Petr. 9: 60. 
nates Virginica Trelease; Branner & Coville, 
Rep. Geol. Surv. Ark. 1884: Part 4, 165. 1891. 
Annual or biennial, diffuse, glabrate, the stems 
ascending, 6’-12’ high. Leaves oblong, narrow, 
deeply pinnatifid, 1/-3’ long, the lower petioled, 
the upper nearly sessile and sometimes reduced 
to lobed or entire bracts; pedicels spreading or 
ascending, 2’ long in fruit; flowers very small, 
white; pods linear, ascending, 8/’’-12/’ long, 
about 1’’ broad; seeds in I row in each cell, 
nearly as broad as the pod, orbicular, wing- 
margined. 
In open places, Virginia and Kentucky to Mis- 
souri, south to Florida and Texas, west to Lower 
California. March-—May. 
Arabis lyrata Y,. Sp. Pl. 665. 1753. 
Cardamine spathulata Michx. FI. Bor. Am. 2.29. 1803. 
Tufted, perennial or biennial, erect, 4/-12’ high, 
glabrous above, pubescent below, or sometimes gla- 
brous throughout. Basal leaves lyrate-pinnatifid, 
1/-2’ long, spatulate or oblanceolate, pubescent or 
glabrous; stem-leaves entire or dentate, spatulate or 
linear, %4/-1’ long; pedicels slender, ascending, 3//— 
4’ long in flower, elongating in fruit; flowers pure 
white, 3/’-4/’ broad; petals much exceeding the 
calyx; pods 9//-15’’ long, linear, ascending, less than 
1’’ broad, their valves firm, nerved; style 14’ long; 
seeds in 1 row, oblong, 1’ long, wingless. 
Rocky and sandy places, Ontario to Virginia and Ken- 
tucky, west to Manitoba and Missouri. Ascends to 2500 
ft.in Virginia. Alsoin Japan. April-Sept. 
Arabis lyrata occidentalis S. Wats.; Robinson in Gray & 
Wats. Syn. Fl. 1: Part 1, 159. 1895. 
Valves of the pod thin, faintly nerved; stigma sessile or 
very nearly so. Lake Erie; British Columbia to Alaska. 
3. Arabis humifusa (J. Vahl) S. Wats. \ > 
Arctic Rock-cress. (Fig. 1773.) aN VEGG 
Sisymbrium humifusum J. Vahl, Fl. Dan. pl. 2297. CS NN 
A. humifusa S. Wats. Proc. Am. Acad. 25:124. 1890. ™ : 
Perennial from a slender root, somewhat pubes- 
cent at least below, or entirely glabrous, the stems 
diffuse or ascending, slender, mostly simple, 3/-6’ 
long. Leaves spatulate or oblong, nearly entire, 
4/’-8’’ long, 1’’-2’” wide, the lower petioled, the 
upper sessile; flowers purplish or white, about 3/’ 
broad; style very short; pods linear, flat, at length 
drooping, 8’’-12’’ long, rather more than 34’ 
wide, the valves very faintly nerved; seeds ob- 
long, wingless, in 2 incomplete rows in each cell; 
cotyledons imperfectly accumbent. 
Greenland and Labrador to Hudson Bay and the 
Northwest Territory. Summer, 
