I 



STANDLEY TKEES AND SHRUBS OF MEXICO 1373 



Tube of the corolla about twice as long as the lobes; leaves appressed- 



pilose beneath, at least along the costa 4. R. armata. 



Corolla pubescent outside; leaves usually pubescent beneath over the 

 whole surface; flowers sessile. 

 Corolla lobes rhombic-obovate; leaves abruptly attentuate to the base. 



5. B. tetracantha. 

 Corolla lobes never obovate; leaves not abruptly attenuate to the base. 



Lower surface of leaves not tomentose 6. R. albonervia. 



Lower surface of leaves densely tomentose, at least when young. 



Corolla tube 5.5 to 6 cm. long 7. R. cinerea. 



Corolla tube 1.5 to 2 cm. long. 



Spines in pairs; leaves 3.5 cm. long or less, rounded at apex. 



8. R. nelsonii. 

 Spines mostly in 4's; leaves usualh' more than 3.5 cm. long, 

 sometimes acute. 

 Corolla tube 1.5 cm. long; leaves mostly acute or acutish, 



0.8 to 2.3 cm. wide 9. R. purpusii. 



Corolla tube 2 cm. long; leaves mostly rounded at apex, 1.5 



to 7.5 cm. wide 10. R. watsoni. 



Flowers and fruit small; corolla 0.4 to 2 cm. long; fruit usually 0.6 to 2 cm. long, 

 rarely slightly larger. 

 Plants unarmed. 



Corolla glabrous outside; leaves sessile 11. R. blepharophylla. 



Corolla pubescent; leaves petiolate 12. R. pringlei. 



Plants armed with spines. 



Throat of the corolla densely white-barbate. 



Pericarp thin, black, lustrous, succulent 13. R. rhagocarpa. 



Pericarp thick and hard, never black or succulent. 



Fruit 1.6 to 2.5 cm. in diameter; leaves mostly orbicular-spatulate. 



26. R. thurberi. 

 Fruit 0.6 to 1.3 cm. in diameter; leaves not orbicular-spatulate. 



Spines scattered in pairs along the branches. Fruit 6 to 8 mm. in 



diameter; seeds 2 to 4 25. R. obcordata. 



Spines mostly in pairs at the ends of the branchlets — 14. R. mitis. 

 Throat of the corolla naked, sometimes sparsely pilosulous but never white- 

 barbate. 



Calyx truncate 15. R. truncata. 



Calyx lobate. 



Pericarp thin, black, lustrous, succulent 13. R. rhagocarpa. 



Pericarp thick and hard, never black and lustrous. 



Spines all or mostly in pairs at the ends of the branchlets. 

 Fruit and calyx tube densely pilose with spreading hairs. 



16. R. malacocarpa. 

 Fruit and calyx tube glabrous or appressed-pilose. 



Leaves densely puberulent beneath 17. R. induta. 



Leaves glabrous beneath or puberulent only along the costa. 

 Corolla 14 to 20 mm. long; fruit 2 to 2.5 cm. long. 



18. R. zalapensis. 

 Corolla 6 to 12 mm. long; fruit 0.7 to 2 cm. long. 



Corolla 6 to 7 mm. long; flowers solitary. 



19. R. chiapensis. 

 Corolla 7 to 11 mm. long; flowers often clustered. 



20. R. laetevirens. 



