BRASSIACEAE. 161 



2. Brassica arvensis (L.) B. S. P. (B. Sinapistrum 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. color adensis. 



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. "'4. 



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. fladnizensis. 



Petals yellow. D. steptocarpa Grayana. 



Stem leafy. 



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



, 10. D. cana. 



Petals yellow. 



Plants 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. 15. D. spectabilis. 



11 



