BRASSIACEAE. 161 



2, Brassica arvensis (L.) B. S. P. (B. Sinapistnim Boiss.) Introduced 

 from Europe and sometimes a troublesome weed in grain fields from Newf. 

 to Alb. and Colo. — Ft. Collins. 



20. ALYSSUM L. 



I. Alyssum alyssoides (L.) Gouan. {A. calycinum L.) In fields and 

 waste places and on hillsides from N. H. and Iowa to N. J. and Colo. ; intro- 

 duced from Europe. — Alt. about 5000 ft. — Boulder. 



21. DRABA L. Whitlow-grass. 



Winter annuals or No. 7 sometimes perennial ; style obsolete. 

 Pods hairy. 



Flowers white ; leaves all crowded on the lower part of the stem ; racemes 

 short on long naked peduncles. 

 Inflorescence even in fruit corymbiform ; petals minute or none. 



I. D. micrantha. 

 Inflorescence in fruit elongated ; petals conspicuous. 2. D. coloradensis. 



Flowers yellow or in age sometimes whitish ; stem more or less leafy throughout. 

 Basal leaves obovate, ovate or oblong ; stem-leaves ample ; pedicels longer 



than the pods. 3- D. nemorosa. 



Basal leaves oblanceolate or oblong ; stem-leaves smaller, oblong-lanceolate ; 

 pedicels shorter than the pods. 4. D. montana. 



Pods glabrous. 



Stem more or less leafy. 



Basal leaves obovate; stem-leaves several, broad. 5. D. lutea. 



Basal leaves oblanceolate ; stem-leaves very few and small. 



6. D. nitida. 

 Stem scapiform or with a single leaf ; leaves in basal rosettes. 



Basal leaves oblanceolate or narrowly spatulate, hirsute. 



7. D. crassifolia. 

 Basal leaves narrowly linear-oblanceolate, glabrous, except the very sparingly 



ciliate margins. 8. D. Parryi. 



Perennials ; style usually evident. 



Plant scapose or nearly so ; leaves ciliate on the margins. 



Petals white. 9- D. Hadnizensis. 



Petals yellow. D. steptocarpa Grayana. 



Stem leafy. 



Petals white ; leaves stellate ; plant usually over i dm. high. 



10. D. cana. 

 Petals yellow. 



Plarits glabrous, except the margins of the leaves, which are occasionally 

 ciliate. 

 Leaves linear or narrowly linear-oblanceolate, thin. 



Leaves much shorter than the flowering stems ; pods lance-linear. 



11. D. chrysantha. 

 Leaves almost equalling the flowering stems ; pods ovate. 



12. D. graminea. 

 Leaves spatulate or broadly oblanceolate, thick. 13. D. crassa. 



Plants decidedly hairy, at least on the stem. 



Pubescence long-hirsute, with simple or slightly branched hairs. 



14. D. streptocarpa. 

 Pubescence dense, mostly of branched or stellate hairs. 



Styles 1.5-2 mm. long; pods glabrous or slightly puberulent. 



Pubescence rather sparse and minute ; stem-leaves usually sharply 

 toothed. IS- D. spectabilis. 



11 



