342 BRASSICACEAE 



coarsely toothed; petals clawed, spatulate, 4 mm. long; pods erect, stellate, 2-3 

 cm. long, about 1 mm. wide, torulose; style about 0.5 mm. long. Sisymbrium 

 humile Hook., not Meyer. Pilosella Richardsonii Rydb. Sandy plains: Mack. 

 -Alta. (? Ore.) B.C. Alaska. Boreal Mont. Je-Jl. 



3. A. virgata (Nutt.) Rydb. Stem 2-4 dm. high, simple or branched; 

 hirsute with branched hairs; basal leaves 2-5 cm. long, oblanceolate, spatulate, 

 or oblong, stellate and somewhat hirsute; petals about 4 mm. long, spatulate; 

 pod erect, 2-3 cm. long, nearly 2 mm. wide, style obsolete. Sisymbrium vir- 

 gatum Nutt. Arabis Brebneriana A. Nels. Plains and hills: Wyo. 'Colo. 

 Plain Submont. Je. 



4. A. stenocarpa Rydb. Stem hirsute with branched hairs; basal leaves 

 oblanceolate, 2-3 cm. long, sinuate-dentate, short-petioled, hirsute-stellate; 

 petals spatulate, 3 mm. long; pod 2.5-4 cm. long, glabrous, scarcely 1 mm. wide. 

 Pilosella stenocarpa Rydb. Dry plains: Sask. Colo. Wyo. Plain. Je-Jl. 



5. A. glauca (Nutt.) Rydb. Stem 2-3 dm. high, glabrous; basal leaves 

 spatulate, entire; stem leaves lanceolate, sagittate at the base; petals spatulate, 

 2 mm. long; pod erect, about 1.5 cm. long, nearly I mm. wide, glabrous; style 

 obsolete. Sisymbrium glaucum Nutt. Prairies: Colo. Ida. Alta. Plain 

 Submont. 



25. CHEIRINIA Link. WILD WALL-FLOWER, PRAIRIE-ROCKET, 



YELLOW PHLOX. 



Annual, biennial, or perennial leafy-stemmed herbs, with appressed 2-branched 

 hairs (the hairs appearing as if attached near the middle). Flowers perfect in 

 terminal racemes, usually rather large. Sepals erect, the outer two gibbous at 

 the base. Petals yellow, brown, or purple, clawed, with spreading blades. 

 Filaments free, unappendaged. Pods elongate-linear, more or less 4-angled, or 

 at least with a strong midrib. Style short; stigma 2-lobed. Seeds in one row 

 in each cell, numerous, marginless or margined at the apex. Cotyledons in 

 our species incumbent or nearly so. [Erysimum L., in part.] 



Petals less than 1 cm. long. 



Petals 4-5 mm. long. 1. C. cheiranthoides. 



Petals 6-10 mm. long. 



Perennials or biennials; pods ascending. 2. C. inconspicua. 



Annuals; pods spreading. 3. C. repanda. 



Petals more than 1 cm. long. 

 Petals light yellow. 



Biennials or short-lived perennials, not cespitose. 



Pods almost terete, slightly compressed, tapering into a style more than 2 mm. 



long. 4. C. arida. 



Pods 4-angled; style only slightly narrower, very short. 



Basal leaves, as well as whole plant, grayish-strigose, not silvery. 



Pods widely spreading, 4-8 cm. long, stout; stem-leaves usually sinuate- 

 dentate. 5. C. aspera. 

 Pods strongly ascending or almost erect, 8-12 cm. long (except in C. 



br achy carp a) . 



Stem-leaves usually sinuately dentate. 6. C. elata. 



Stem-leaves entire or rarely denticulate. 



Stem-leaves linear or nearly so; pod usually twisted, slender. 



7. C. asperrima. 

 Stem-leaves oblanceolate; pod straight, stout. 



Pod about 8 cm. long, 1.5 mm. thick. 8. C. oblanceolata. 

 Pod 4-6 cm. long, 2.5 mm. thick. 9. C. brachycarpa. 



Basal leaves, at least, silvery white; stem-leaves narrowly linear. 

 Plant 2-3 dm. high; stem-leaves sinuate-dentate. 



10. C. Bakeri. 



Plant 1-2 dm. high; stem-leaves entire. 11. C. argillosa. 



Low cespitose perennials. 



Leaves entire-margined or minutely denticulate. 12. C. nivalis. 



Leaves sinuate-dentate. 13. C. radicata. 



Petals varying from orange to brown or purple. 



Plant simple, 3-5 dm. high; basal leaves 5-10 cm. long, oblanceolate. 



14. C. Wheeleri. 

 Plant cespitose, 1-2 dm. high; basal leaves 2-4 cm. long, spatulate. 



Perennial with a branched caudex; stem usually more than 1 dm. high. 



15. C. amoena. 

 Biennial; stem in flower a few cm. high, more elongate in fruit, leafy only at 



the base. 16. C. Pallasii. 



