Ambis. CRUCTFER^. 159 



44. ARABIS, L. Rock Cress. (Name from the country Arabia.) — 

 Annuals or perennials mostly of erect habit, nearly all of the Northern Tem- 

 perate and Arctic Zones. Pubescence bi'anched or stellate, rarely simple or 

 none. Flowers white, purple, or more rarely stramineous, in more or less elon- 

 gated racemes. Leaves mostly lanceolate or spatulate, entire, dentate, or less 

 frequently pinnatifid. — Gen. no. 544; DC. Syst. ii. 213; Reichenb. Ic. Fl. 

 Germ. ii. t. 33-44 ; Gray, Gen. 111. i. 58 ; Benth. & Hook. Gen. i. 69. Tiu'- 

 i-itis, L. Gen. no. 546. [By S. Watson.] 



§ 1. SiSYMBRiNA, Watson.^ Sceds oblong or elliptical, very small, wing- 

 less ; cotyledons often more or less oblique. Biennial or perennial. Pubescence, 

 if any, usually simple upon the upper parts, but invariably forked to some extent 

 when present upon the lowest leaves. 



* Leaves all piuiiately divided ; segments filiform. 



A.* filifolia, Greene. A delicate glabrous somewhat glaucous annual, 8 inches to a foot iu 

 height, stem flexuous or somewhat geniculate and branched above : flowers roseate or 

 purple : petals obovate, patulous, 2 to 3 lines iu length, about twice the length of the calyx : 

 pods narrowly linear, acute, about 15 lines iu length, spreadiug-ascending. — Bull. Calif. 

 Acad. Sci. ii. 390. Cardamine JiUfoUa, Greene, Pittonia, i. 30. — Santa Cruz Isl., Calif., 

 Greene, Brandegee. A species of doubtful position. Mature seeds have not been seen. A. 

 pectinata, Greene, Pittonia, i. 287, of Lower California, is nearly related. 

 * * Radical leaves lyrately piuuatifid ; segments short and broad ; cauline not auriculate 

 at the base. 



A. lyrata, L. Slender, branching from the. base, glabrous or rarely somewhat hairy at the 

 base : the stems ascending, a foot high or less : basal leaves with few and small lateral seg- 

 ments or pinnately lobed, often all entire, oblauceolate or spatulate to linear : petals white 

 or pinkish, 2 to 4 lines loug . pods ascending on slender pedicels 3 to 6 lines long, very nar- 

 row with a short stout style, straight or slightly curved; the valves rather tliick, firm, aud 

 nerved nearly to the top. — Spec. ii. 665. A. petrcea, Gray, Man. ed. 5, 67, in part. iSisyin- 

 briuni arabidoides, Hook. Fl. Bor.-Am, i. 63, t. 21, at least in part. Cardamine spathulata, 

 Michx. Fl. ii. 29. — From the Great Lakes to Connecticut and New Jersey, aud southward 

 along the Alleghauies to N. Carolina and Tennessee.- Southward it becomes decidedly 

 perennial, with more lax aud slender stems, and the pods with thinner aud scarcely nerved 

 valves. No seeds have been examined with cotyledons so strictly iucumbent as figured and 

 described by Hooker. 



Var. occidentalis, Watson, n. var. Pods with sessile stigma or a very short and 

 thick style ; the valves ratlier thin but often faintly nerved to the top. — A. ambic/ua, DC. 

 Syst. ii. 231, in part; Torr. & Gray, Fl. i. 81. ^4. petnea, var., Kegel, Bull. Soc. Nat. Mosc. 

 XXXV. pt. 2, 163. — From Alaska to British Columbia and the eastern side of the Rocky 

 Mts. in Brit. America ; Point Pelee on Lake Erie, l/aco«)i. (Kamtschatka, Wright.) The 

 true A. petrcea, Lam., as it occurs in Europe, appears to be distinguished from all American 

 forms by its usually broader and blunter pod, more broadly elliptical or nearly orbicular 

 seed, and the cotyledons strictly accumbent. The Greeuland specimens referred to this 

 species as a variety, with pilose siliques aud pedicels (Lange, Medd. Green, iii. 49), are more 

 probably the same as Hooker's Sisymbrium humile. 



* * * Radical leaves oblauceolate, toothed or entire. 

 ■h— Cauline leaves not auriculate. 



A. humiftisa, Watson. Glabrous, l)ranching from the base ; the low decumbent stems 6 

 inches high or less, simple or branclied : radical leaves usually numerous, few-toothed, an 

 inch long or less , the petioles rarely slightly ciliate ; cauline leaves spatulate-oblanceolate, 



i Pseudarabis, Wats, in Gray, Man. ed. 6, 67, & Proc. Am. Acad. xxv. 124, but not of Endl., 

 which, being Pseudoarabis of C. A. Meyer, depends upon a diflferent subdivision of the genus. 

 2 S. Missouri, Eggert. 



