GENUS 33. 



MUSTARD FAMILY. 



i. Arabis virginica (L.) Trelease. Vir- 

 ginia Rock-cress. Fig. 2069. 



Cardamine virginica L. Sp. PI. 656. 1753. 

 Cardamine ludoviciana Hook. Journ. Bot. 1 : 191. 



1834- 



A. ludoviciana Meyer, Ind. Sem. Petr. 9: 60. 1842. 

 Arabis virginica Trelease ; Branner & Coville, Rep. 



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

 Planodes virginicum Greene, Leaflets 2: 221. 1912. 



Annual or biennial, diffuse, glabrate, the stems 

 ascending, 6'-i2 r high. Leaves oblong, narrow, 

 deeply pinnatifid, i'~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"-i2" long, about 

 i" broad; seeds in I row in each cell, nearly as 

 broad as the pod, orbicular, wing-margined. 



In open places, Virginia and Kentucky to Illinois, 

 Kansas, Arkansas, south to Florida and Texas, west 

 to southern and Lower California. March-May. 



2. Arabis lyrata L. Lyre-leaved Rock-cress. 

 Fig. 2070. 



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



Cardamine spathulata Michx. Fl. Bor. Am. 2: 29. 1803. 



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

 Wats. Syn. Fl. i : Part i, 159. 1895. 



Tufted, perennial or biennial, erect, 4'-i2' high, gla- 

 brous above, pubescent below, or sometimes glabrous, 

 throughout. Basal leaves lyrate-pinnatifid, I '-2' long, 

 spatulate or oblanceolate, pubescent or glabrous ; stem- 

 leaves entire or dentate, spatulate or linear, i'-i' long; 

 pedicels slender, ascending, 3" -4" long in flower, 

 elongating in fruit ; flowers pure white, 3"-4" broad ; 

 petals much exceeding the calyx; pods p"-is" long, 

 linear, ascending, less than i" broad, their valves firm, 

 nerved; style \" long or less; seeds in I row, oblong, 

 i" long, wingless. 



Rocky and sandy places, Ontario to Connecticut, Vir- 

 ginia and Tennessee, west to Manitoba, Alaska, British Co- 

 lumbia and Missouri. Ascends to 2500 ft. in Virginia. Also 

 in Japan. April-Sept. 



3. Arabis arenicola (Richards.) Gelert. Arctic 

 Rock-cress. Fig. 2071. 



Entrema arenicola Richards. ; Hook. Fl. Bor. Am. i : 67. 



.1833- . 

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



1840. 



A. humifusa S. Wats. Proc. Am. Acad. 25: 124. 1890. 

 A. arenicola Gelert, Bot. Tidskr. 21 : 270. 1898. 



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 i" wide, the valves 

 very faintly nerved; seeds oblong, wingless, in 2 

 incomplete rows in each cell; cotyledons imperfectly 

 accumbent. 



Greenland and Labrador to Hudson Bay and the 

 Northwest Territory. Summer. 



