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. 



Sti-ins simple or branched from the base only. 



Mature silique short (2 cm. or less) ...!. 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. (Cheiranthus 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- 

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

 is 1 . )'.).) Desert regions of south-central Wyoming and extending southward 

 into (,'olorado. 



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

 I>"\\ mult icipital perennial, bearing separate tufts of leaves and as many 

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

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

 lar^e, 11 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, with 



