338 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



This large family, chiefly of temperate regions, includes such well- 

 known garden vegetables and culinary herbs as cabbage, cauliflower, 

 turnip, radish, cress, and mustard. Many of the species found in 

 Arizona are weeds of Old World origin. Few of them have any con- 

 siderable value as forage, but it happens that species of Lepidium, 

 Lesquerella, Descurainia, etc., although avoided while the plants 

 are green, are relished, especially by horses, when the pods are ripe. 

 It has been reported that hay containing mature plants of Sisymbrium, 

 Brassica, Camelina, Conringia, etc., may cause disorders in livestock, 

 because of the oil of mustard in the seeds. Plants of certain genera 

 {Stanley a, Descurainia, etc.) are used as potherbs by the Indians. 



There is much difference of opinion concerning the limits of genera 

 in the Cruciferae, and it is probable that some of the generic segregates 

 made by Kydberg, Schulz, and others and accepted in this publication 

 should be reduced to subgeneric rank. 



Key to the genera 



1. Capsules 1-celled, 1-seeded, indehiscent, thin and flat, orbicular or nearly so; 

 pedicels strongly decurved in fruit (2) . 

 2. Pubescence, if any, of simple hairs; pods with conspicuous, commonly per- 

 forate wing-margins, not bearing hooked hairs __ 29. Thysanocarpus. 



2. Pubescence partly of branched hairs; pods wingless, bearing hooked hairs. 



30. Athysanus. 

 1. Capsules 2-celled, normally containing 2 or more seeds (3). 



3. Pods strongly compressed contrary to the very narrow partition, not more 



than twice as long as wide (4) . 

 4. Capsules didymous (twinlike), wider than long, indehiscent or tardily 

 dehiscent; plants copiously or densely stellate-pubescent (5). 

 5. Plant not lepidote; pods flat; seed solitary in each cell_ 22. Dithyrea. 



5. Plant silvery-lepidote; pods inflated; seeds commonly more than one 



in each cell 23. Physaria. 



4. Capsules not didymous, at most obcordate, regularly dehiscent, but 

 tardily so in Lyrocarpa (6). 



6. Seed solitary in each cell; pubescence, if any, of simple hairs. 



10. Lepidium. 

 6. Seeds 2 or more in each cell (7). 



7. Plants glabrous; leaves entire or merely dentate, those of the stem 



auriculate-clasping 11. Thlaspi. 



7. Plants mostly pubescent with stellate hairs (8). 



8. Petals brown purple, 15 to 20 mm. long; pods more or less irregular 

 in shape, often lobed at apex; plant perennial. 



21. Lyrocarpa. 

 8. Petals white or whitish, small; plants annual (9). 



9. Plant glabrous or stellate-puberulent; stems very slender; leaves 

 mostly petioled, entire or few-toothed; pods somewhat tur- 

 gid, elliptic, entire at apex 25. Hutchinsia. 



9. Plant more or less hirsute below; stems relatively stout; stem 

 leaves sessile, auriculate, the basal ones pinnatifid; pods flat, 



obdeltoid, notched at apex 26. Capsella. 



3. Pods not compressed contrary to the partition (although sometimes appear- 

 ing so in dried specimens), dehiscent (10). 

 10. Capsules not more than twice as long as wide (11). 



11. Pods flat, strongly compressed parallel to the broad partition; herbage 



commonly with stellate or forked hairs 28. Draba. 



11. Pods more or less turgid (12). 



12. Valves of the obovoid pods with a distinct central nerve extending 

 from base to apex; leaf blades entire or denticulate. 



27. Camelina. 



12. Valves of the ovoid, ellipsoid, or globose pods without a distinct 



central nerve, or the nerve not extending to the apex (13). 



13. Seeds plump; herbage glabrous or sparsely pubescent with simple 



hairs; leaf blades pinnate or pinnatifid; aquatic or marsh plants. 



19. Rorippa. 



