. II.] 



MUSTARD FAMILY. 



147 



i. Arabis Virginica (L,.) Trelease. Virginia Rock-cress. (Fig. 1771 



Cardamine Virginica L,. Sp. PI. 656. 1753. 

 Cardamine Ludoviciana Hook. Journ. Bot. i: 191. 



1834. 

 Arabis Ludoviciana Meyer, Ind. Sem. Petr. 9: 60. 



1842. 

 Arabis Virginica Trelease; Branner & Coville, 



Rep. Geol. Surv. Ark. 1884: Part 4, 165. 1891. 



Annual or biennial, diffuse, glabrate, the stems 

 ascending, 6 / -ia / high. I/eaves oblong, narrow, 

 deeply pinnatifid, I'-s'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 // -i2 // long, 

 about i x/ 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. 



2. Arabis lyrata I,. Lyre-leaved Rock-cress. (Fig. 1772.) 



Arabis lyrata L. Sp. PI. 665. 1753. 

 Cardamine spathulata Michx. Fl. Bor. Am. 2. 29. 



1803. 



Tufted, perennial or biennial, erect, 4 / -i2 / high, 

 glabrous above, pubescent below, or sometimes gla- 

 brous throughout. Basal leaves lyrate-pinnatifid, 

 i / -2 / long, spatulate or oblanceolate, pubescent or 

 glabrous; stem-leaves entire or dentate, spatulate or 

 linear, ^'-l' 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 // -i5 // long, linear, ascending, less than 

 i" broad, their valves firm, nerved; style X" l n g; 

 seeds in i row, oblong, X /x l n g> wingless. 



Rocky and sandy places, Ontario to Virginia and Ken- 

 tucky, west to Manitoba and Missouri. Ascends to 2500 

 ft. in Virginia. Also in Japan. April-Sept. 



Arabis lyrata occidentalis S. Wats. ; Robinson in Gray & 



Wats. Syn. Fl. i: Part i, 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.) 



Sisymbrium humifusum J. Vahl, Fl. Dan. pi. 2297. 

 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, i "-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 // -i2 // long, rather more than %" 

 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. 



