MUSTARD FAMILY 305 



high. Leaves all pinnately divided, the segments filiform, 20-25 mm. long; flowers racemose, 

 rose-purple ; petals 5-6 mm. long, the blade broadly obovate, narrowed to a claw ; fruiting pedi- 

 cels short ; pods ascending, very narrowly linear, 3-4 cm. long, acute ; seeds in 1 row, wingless, 



Canyons, Upper Sonoran Zone; Santa Cruz and Santa Catalina Islands, southern California. Type 

 locality: Santa Cruz Island. April. 



2. Arabis deserti (M. E.. Jones) Abrams. Desert Rock-cress. Fig. 2098. 



Thelypodium deserti M. E. Jones, Contr. West. Bot. No. 12: 1. 1908. 



Slender annual, 15-30 cm. high, branching from or usually above the base, the branches 

 slender, ascending, glabrous or sparsely puberulent with forked hairs. Basal leaves 3-5 cm. 

 long, deeply pinnatifid into several rather distant linear to oblanceolate lobes, some of the lobes 

 often again lobed near the base on the upper margin; stem leaves subtending the branches nar- 

 rowly linear, entire or few-toothed or rarely lobed ; racemes loose and rather weak, elongated, 

 usually well exceeding the stem proper; sepals oblong-ovate, 1.5 mm. long, sparsely puberulent 

 with forked hairs to subglabrous, scarious-margined ; petals white, 2.5 mm. long, the blade 

 scarcely 1 mm. wide but little broader than the claw, rounded or obtuse at apex; anthers 0.5 mm. 

 long; pods 10-20 mm. long, 1 mm. wide, compressed, ascending, straight or slightly arcuate, 

 beak 1-2 mm. long ; pedicels spreading or ascending, 1-3 mm. long ; seed oblong, not winged. 



Rock crevices and gravelly washes, lower Sonoran Zone; Emigrant Canyon, Panamint Mountains, and 

 Death Valley, California, and Amargosa Desert, Nevada. Type locality: Amargosa Desert. March-May. 



3. Arabis virginica (L.) Trelease. Virginia Rock-cress. Fig. 2099. 



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



Cardamine Lndoviciana Hook. Journ. Bot. 1: 191. 1834. 



Arabis Ludoviciana C. A. Mey. Ind. Sem. Petrop. 9: 60. 1842. 



Arabis virginica Trelease ex Branner & Coville, Rep. Geol. Surv. Ark. 1884: 165. 1891. 



Planodes virginica Greene, Leaflets Bot. Obs. 2: 221. 1912. 



Annual or rarely biennial, glabrate, the stems ascending or decumbent, 15-30 cm. long. 

 Leaves oblong, deeply pinnatifid, 25-70 mm. long, the lower petioled, the upper nearly sessile; 

 pedicels spreading or ascending, 4 mm. long in fruit; flowers very small, white; pods linear, 

 ascending, 15-25 mm. long, about 2 mm. wide; seeds orbicular, wing-margined, nearly as broad 

 as the pod. 



In desiccated vernal pools, Sonoran Zones; southern California and Lower California to Virginia, Florida, 

 and Texas. Type locality: Virginia. March-May. 



4. Arabis lyrata subsp. kamchatica Fisch. Kamchatka or Western Rock-cress. 



Fig. 2100. 



Arabis ambigua var. intermedia DC. Syst. 2: 231. 1821. 



Arabis lyrata var. /3 DC. loc. cit. 



Arabis kamchatica Fisch. ex DC. loc. cit. as a synonym. 



Arabis lyrata var. occidentalis S. Wats, in A. Gray, Syn. Fl. N. Amer. I 1 : 159. 1895. 



Arabis lyrata subsp. kamtschatica Fisch. ex Hulten, Fl. Aleut. Isl. 202. 1937; spelling altered from the original. 



Perennial, glabrous or sparingly pubescent at base, the stems slender, branched at the base, 



2-4 dm. high. Basal leaves 2-4 cm. long, lyrately lobed ; stem leaves spatulate, entire or toothed ; 



petals white, about 6 mm. long ; fruiting pedicels ascending, about 1 cm. long ; pods erect or 



nearly so, 2-3 cm. long, 1 mm. wide ; stigma sessile or on a very short thick style ; seeds oblong, 



wingless. 



Wet rocky places, Boreal Zones; Alaska to northern Washington, Alberta, and Montana, also eastern Asia. 

 Type locality: "in Kamchatka." May-Aug. 



5. Arabis Nuttallii Robinson. Nuttall's Rock-cress. Fig. 2101. 



Arabis Nuttallii Robinson in A. Gray, Syn. Fl. N. Amer. I 1 : 160. 1895. 



Arabis spathulata Nutt. in Torr. & Gray, Fl. N. Amer. 1: 81. 1838. Not DC. 1821. 



Biennial or usually perennial, more or less cespitose, the stems erect or ascending, 1-3 dm. 

 high, sparingly hirsute toward the base. Basal leaves spatulate, short-petioled, 1-3 cm. long, 

 entire; stem leaves oblanceolate, sessile; petals white, 4-6 mm. long; pedicels 8-15 mm. long, 

 pods 1-3 cm. long, about 1 mm. broad, somewhat attenuate to a stout style; valves 1-nerved; 

 seeds elliptical, wingless. 



Arid Transition and Upper Sonoran Zones; eastern Washington to Montana and Utah. Type locality: 

 "Lofty dry hills of the Platte, from the Black Mountains to the Central Chain." May-July. 



6. Arabis macella Piper. Piper's Rock-cress. Fig. 2102. 



Arabis macella Piper, Proc. Biol. Soc. Wash. 33: 103. 1920. 



Biennial from a stout taproot, the stems several, 4-5 dm. high, slender, simple, flexuous, 

 sparsely pilose below, otherwise glabrous. Basal leaves spatulate-oblong, 3 cm. long, the blade 

 longer than the margined petiole, ciliate on the margins ; stem leaves oblong or linear ; racemes 

 5—15 cm. long; pedicels spreading in fruit, 10-15 mm. long, glabrous; petals oblong-spatulate, 

 white; pods erect, 15-20 mm. long, 1 mm. wide, somewhat compressed, glabrous; valves 3- 

 nerved; style 1.5 mm. long; seeds in 1 row, wingless. 



Upper Sonoran and Arid Transition Zones; known only from the vicinity of the type locality near Ritz- 

 ville, Adams County, Washington. May-June. 



