356 (.'ONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



Branches not glandular. 

 Calyx distinctly dentate. 1 to 1.5 mm. long, a third to half as 

 long as the corolla. 



Fruit about 4 mm. wide, unarme'd 15. M. coelocarpa. 



Fruit about 6 mm. wide, often spiny. 



Spines dark-colored, not much broadened at the base; 



fruit unarmed 16. M. wrightii. 



Spines usually light-colored, very broad and flat at base; 

 fruit armed with spines on the margins. 



17. M. dysocarpa. 

 Calyx subtruncate, about 0.8 mm. long, about a fourth as long 

 as the corolla. 



Pinnae 3 or 4 pairs 18. M. luisana. 



Pinnae 9 to 20 pairs. 

 Leaflets glabrous on the upper surface. 



19. M. rhododactyla. 

 Leaflets tomentulose-sericeous on both surfaces. 



Fruit unarmed or nearly so 20. M. palmeri. 



Fruit densely armed with spines 21. M. loenthami. 



AA. Flowers capitate. 



B. Stamens of the same number as the corolla lobes. 

 Pinnae one pair ; leaflets 1 or 2 pairs, usually large. 



Stems copiously pubescent or setose 22. M. albida. 



Stems glabrous or nearly so. 

 Plants unarmed or nearly so ; leaflets 1.7 cm. long or shorter. 



23. M. goldmanii. 

 Plants armed with spines ; leaflets mostly 2.5 to 8 cm. long. 

 Pods sessile or nearly so ; leaflets setose beneath. 



24. M. manzanilloana. 



Pods stipitate; leaflets glabrous beneath 25. M. acapulcensis. 



Pinnae usually 2 to several pairs, sometimes one pair; leaflets 3 to many 

 pairs, usually small. 



Pinnae 3 to 5 pairs 26. M. leptocarpa. 



Pinnae 1 or 2 pairs. Fruit (so. far as known) less than 1 cm. wide. 

 Leaflets 3 to 5 or rarely 6 pairs, 7 to 25 mm. wide. 



Leaflets 2 cm. long or shorter, glabrous 27. M. lactiflua. 



Leaflets 2.3 to 3.6 cm. long, more or less pubescent. 



Fruit strigose ; leaflets strigose 28. M. deamii. 



Fruit glabrous ; leaflets soft-pubescent when young. 



29. M. psilocarpa. 

 Leaflets more than 5 pairs in most of the leaves, less than 7 mm. wide. 

 Peduncles glabrous or merely puberulent. 



Fruit densely spiny 30. M. sicyocarpa. 



Fruit unasrmed, except sometimes on the margin. 



Plants unarmed; margin of the fruit spiny 31. M. caerulea. 



Plants armetl with stout spines; fruit unarmed. 



32. M. mixtecana. 

 Peduncles densely pilose, toraentose, scabrous, or hispid. 

 Fruit glabrous but spiny ; plants chiefly herbaceous. 



34. M. pudica. 

 Fruit puberulent or pilose as well as spiny ; plants woody almost 

 throughout. 



Leaflets glabrous on the upper surface 34. M. nelsonii. 



Leaflets densely pubescent on both surfaces 35. M. xanti. 



