230 CRUCIFERAE (MUSTARD FAMILY) 



large and yellow (sometimes orange-red, brownish, or rose-purple). Sepals 

 erect, one pair strongly gibbous at base. Petals long-clawed, with a flat 

 blade. Silique more or less 4-angled, sessile; stigma 2-lobed. Seeds nu- 

 merous. Cheiranthus of some Am. authors. 



Biennials. 



Stems simple or branched from the base only. 



Mat uresiiique short (2cm. or less) ...... 1. E. cheiranthoides. 



Mature silique long (3 cm. or more). 



Flowers small; petals 6-10 mm. long . . . . . 2. E. inconspicuum. 



Flowers large; petals 12-20 mm. long. 



Silique obtusely angled, with convex sides . . . . 3. E. asperum. 



Silique sharply angled, with flat sides 4. E. asperrimum. 



Stems usually paniculately branched from the base upward . 5. E. aridum. 

 Perennials. 



Low and somewhat caespitose; flowers yellow . . . . 6. E. nivale. 

 Taller, the caudex subsimple; flowers orange, reddish, or rose- 

 purple 7. E. Wheeled. 



1. Erysimum cheiranthoides L. Sp. PI. 661. 1753. Minutely rough- 

 pubescent, rather slender and erect, 3-8 dm. high: stems more or less branched: 

 leaves lanceolate, entire or nearly so: flowers only 5 or 6 mm. long, yellow: 

 silique linear, obtusely 4-angled, 15-25 mm. long, nearly erect on short di- 

 vergent pedicels; style short (1 mm.). TREACLE MUSTARD. Frequent, on 

 stream banks; across the continent. 



2. Erysimum inconspicuum (Wats.) MacM. Met. Minn. 268. 1892. Scabro- 

 canescent, the hairs 2-rayed and appressed (appearing as if affixed by the mid- 

 dle): stems simple or slightly branched, one or more from the crown: leaves 

 linear or lanceolate, usually entire, crowded on the crown and the lower part 

 of the stem: flowers small, the petals about 8 mm. long: silique erect, 3-5 cm. 

 long; the valves convex, strongly nerved; pedicels somewhat spreading. 

 Erysimum parviflorum. Kansas and Colorado, and far to the north and west. 



3. Erysimum asperum DC. Syst. 2: 505. 1821. Greenish-canescent with 

 appressed hairs (2-rayed as in the preceding): stems single and simple or 

 nearly so, 2-5 dm. high: leaves oblanceolate or narrowly spatulate, entire or 

 repandly toothed; the cauline mostly entire and upwardly becoming linear- 

 lanceolate: flowers large and very typically cruciform, in a compact raceme, 

 which is short even in fruit: petals yellow or often changing to orange, 

 brownish-red, or rose-purple, 12-20 mm. long: siliques obtusely 4-angled, 

 widely and regularly divaricate, 5-8 cm. long. (Cheiranihvs Bakeri Greene, 

 Pitt. 4: 235. 1901; Erysimum oblanceolatum Rydb. Bull. Torr. Bot. Club 

 31: 557. 1904.) From beyond the Mississippi to California. 



4. Erysimum asperrimum (Greene) Rydb. Bull. Torr. Bot. Club 33: 141. 

 1906. Much like the preceding but more roughly and densely canescent, 

 usually low, 1-3 dm. high: flowers smaller, 10-14 mm. high: silique long, 

 sharply 4-angled, the sides very flat. (Erysimum pumilum Rydb.; not E. pu- 

 milum Nutt.) On the high plains of northern Colorado and Wyoming. 



5. Erysimum aridum A. Nels. Green but appressed-pubescent with 

 minute 2-parted hairs: stem single from the enlarged crown of the taproot, 

 more or less paniculately branched from the base up, 2-3 dm. high: the crown 

 leaves early deciduous; the cauline oblanceolate to lance-linear, entire or 

 nearly so: racemes many, elongated in fruit: petals yellow, 16-20 mm. long: 

 siliques 8-12 cm. long, subterete, but the valves distinctly 1-nerved, curved- 

 ascending. (Cheiranthus aridus A. Nels. Bull. Torr. Bot. Club 26: 351. 

 1899.) Desert regions of south-central Wyoming and extending southward 

 into Colorado. 



6. Erysimum nivale (Greene) Rydb. Bull. Torr. Bot. Club 31: 558. 1904. 

 Low multicipital perennial, bearing separate tufts of leaves and as many 

 short flowering stems, 5-15 cm. high: leaves green but somewhat pubescent 

 with appressed 2-parted hairs, linear to lanceolate, entire or nearly so: petals 

 large, 14-18 mm. long, the blade relatively small: siliques suberect, nearly 

 terete, taper-pointed. (E. radicatum Rydb. 1. c.) Subalpine heights of the 

 Colorado mountains. 



7. Erysimum Wheeleri Wats. Wheeler Rep. 6: 64. 1878. Perennial, w;th 



