350 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



6. Draba cana Rydb. Frequent on the east slope at low and middle altitudes 

 and sometimes above timber line, in woods or on open hillsides. B. C. and Alta. to 

 N. Mex. — Stems stout, branched, at least at the base; finely hairy; leaves mostly 

 lanceolate or ovate; petals 3 mm. long; pods 6 to 8 mm. long, finely hairy, usually 

 twisted . 



6. Draba aurea Vahl. Frequent on the east slope at middle altitudes and some- 

 times above timber line, in woods or on open hillsides. Alaska to Ariz., Lab., and 

 Greenl.; also in Eur. — Stems stout, finely hairy; basal leaves oblanceolate, 1 to 2 

 cm. long; petals 3 to 5 mm. long; pods 10 to 12 mm. long, 2 to 3 mm. wide, finely 

 hairy, usually twisted. 



7. Draba densifolia Nutt. Occasional above timber line, chiefly on rock slides. 

 Alaska to Wyo. — Plants densely tufted ; leaves oblanceolate, 5 to 10 mm. long, hairy, 

 crowded and overlapping; stems 1 to 5 cm. high; petals yellow, 4 to 5 mm. long; 

 pods 5 to 8 ram. long, 3 to 4 mm. wide. 



8. Draba andina (Nutt.) A. Nels. Occasional above timber line, on rock slides or 

 exposed summits, sometimes about snow banks at middle altitudes. B. C. and Alta. 

 to Wyo. and Utah.— Plants very densely tufted; leaves 5 mm. long, hairy, densely 

 crowded and overlapping; stems 1 to 3 cm. high; petals yellow, 4 to 5 mm. long; 

 pods 3 to 4 mm. long, 2.5 to 3 mm. wide. 



9. Draba oligosperma Hook. Hills at east entrance, Umbach. Alaska to Calif, 

 and Utah. — Plants densely tufted; leaves linear, 5 to 10 mm. long, crowded; stems 

 2 to 8 cm. high; petals pale yellow, 4 to 5 mm. long; pods about 4 mm. long and 3 

 mm. wide. 



10. Draba fladnizensis Wulf. Open rocky slope at Gunsight Pass. Alaska to 

 Colo., Que., and Greenl.; also in Eur. — Stems slender, 5 to 12 cm. high; leaves 

 oblanceolate, 1 cm. long or shorter, nearly glabrous; petals white, 3 mm. long; pods 

 4 to 6 mm. long, 2 mm. wide. 



11. Draba glacialis Adams. Occasional above timber line, on cliffs or open rocky 

 slopes. Alaska to Wyo. and Greenl. — Stems 5 to 15 cm. high, densely tufted; leaves 

 mostly linear, 1 to 3 cm. long, finely hairy; petals yellow, 5 mm. long; pods 6 to 10 

 mm. long, 2 to 3 mm. wide. 



12. Draba lonchocarpa Rydb. Occasional above timber line, on moraines and 

 rock slides. B. C, Wash., Mont., and Alta.^ — Plants slender, tufted, 5 to 10 cm. high; 

 leaves spatulate, 3 to 10 mm. long; petals white, 2 mm. long; pods 8 to 12 mm. long, 

 1.5 mm. wide. 



13. Draba oreibata Macbr. & Payson. Occasional on open rocky slopes about 

 timber li ne, or in exposed places at lower altitudes. Idaho, Utah, and Mont. — Plants 



tufted, 3 to 10 cm. high; leaves narrowly oblong, 4 to 10 mm. long; petals white, 

 2 to 3 mm. long; pods 7 to 10 mm. long, 2 to 3 mm. wide. 



18. ARABIS L. RocKCRESS. 



Perennials or biennials, glabrous or hairy, the hairs usually branched; leaves entire 

 or toothed, rarely lobed; petals white, pink, or purple; pods long, linear, flat. 



Basal leaves deeply lobed 1. A. ambigua. 



Basal leaves entire or toothed. 

 Pods spreading or reflexed. 

 Pedicels abruptly reflexed. 



Pods nearly 2 mm. wide; petals G to 8 mm. long; stem leaves oblong or lan- 

 ceolate 2. A. retrofracta. 



Pods less than 1.5 mm. wide; petals 5 to 6 mm. long; stem leaves linear. 



3. A. lignipes. 



