5(4). Petals white to lavender; inflorescences racemose, none of the flowers 

 pedunculate; styles less than 3 mm. long (6) 



5. Petals yellow; at least some flowers pedunculate or styles over 5 mm. long; 



pedicels much-elongated (9) 



6(5). Valves not extending to silique margin, elastic and rolling up after dehis- 

 cence 6. Cardainine 



6. Valves extending to edge of the replum margin, not elastic and rolling upon 



dehiscence (7) 



7(6). Siliques linear-elliptical; seeds wingless, in 2 distinct rows in each loculus.... 

 13. Draba 



7. Siliques linear; seeds winged, in a single row in the loculus (8) 



8(7). Leaves entire to dentate; pedicels expanded below receptacle 2. Arabis 



8. Leaves pectinate to pinnatifid; pedicels not expanded below receptacle 



3. Sibara 



9(5). Leaves pinnately or bipinnately dissected; siliques thick, spongy and mar- 

 gined or the styles over 5 mm. long 11. Selenia 



9. Leaves lyrately lobed to entire; siliques flattened, not thick and spongy nor mar- 



gined; styles less that 2 mm. long 12. Leavenworthia 



10(4). Cauline leaves petiolate or cuneate at base, upper ones entire 2. Arabis 



10. Cauline leaves sessile and auriculate, upper ones lobed 3. Sibara 



11(3). Leaves entire or lobed, never divided as far as midrib (12) 



11. Leaves (at least some) pinnately lobed to bipinnate, the primary lobes cut 



to the leaf rachis ( 1 5 ) 



12(11). Flowers yellow or yellowish, never white to lavender 7. Rorippa 



12. Flowers white to lavender, never yellow (13) 



13(12). Upper cauline leaves auriculate 3. Sibara 



13. Upper cauline leaves petiolate or cuneate at base (14) 



14(13). Lower cauline leaves auriculate; cotyledons accumbent 1. lodanthus 



14. Lower cauline leaves petiolate or cuneate at base; cotyledons incumbent 



4. Sisymbrium 



15(11). Trichomes mostly highly branched; stems and leaves often grayish from 



a dense pubescence; leaves often bipinnate to tripinnate 



5. Descurainia 



15. Trichomes mostly simple or absent; stems and leaves greenish; leaves at most 



pinnate plus secondary lobing (16) 



16(15). Petals yellow or yellowish (17) 



1 6. Petals white to lavender (18) 



17(16). Cauline leaves auriculate or clasping stem at base 9. Barbarea 



17. Cauline leaves not auriculate or clasping stem 4. Sisymbrium 



18(16). Plants aquatic or of very wet habitats; valves of siliques nerveless; cauline 

 leaves pinnate to bipinnate 7. Rorippa 



18. Plants terrestrial, ubiquitous in habitats, either dry or wet; valves of siliques 



nerved; cauline leaves at most lobed 4. Sisymbrium 



19(1). Weak aquatic perennial with capillary-dissected submerged leaves; petals 

 white 8. Armoracia 



19. Terrestrial annuals in wet or dry habitats, if in water the petals yellow (20) 



20(19). Siliques strongly flattened at right angles to septum, the replum much 

 narrower than silique width, broader above than below, more or 

 less triangular to heart-shaped in outline 14. Capsella 



963 



