STANDLEY TREES AND SHRUBS OF MEXICO. 1291 



Flowers in few-flowered lateral umbels or racemes. 

 Pubescence of the leaves of simple hairs. 



Corolla about 5 mm. long 28. S. nigrum. 



Corolla about 10 mm. long 30. S. xanti. 



Pubescence none or of branched hairs. 



Young branchlets with a feltlike tomentum_31. S. brachystachys. 

 Young branchlets glabrous or obscurely puberulent. 

 Leaves acuminate ; pedicels usually recurved in fruit. 



32. S. nudum. 

 Leaves mostly obtuse ; pedicels erect in fruit__33. S. diphyllum. 

 A A. Anthers more or less elongate, the terminal pores posterior or directed 

 upward ; plants nearly always armed with prickles. 

 D. Prickles of the stems strongly recurved; leaves not prickly on the upper 

 surface. 

 Leaves glabrous on the upper surface, or pubescent with simple hairs. 



Leaves entire 34. S. oaxacanum. 



Leaves all or mostly pinnate-lobate 35. S. refractum. 



Leaves sparsely or densely stellate-pubescent on the upper surface. 



Branches glabrous or nearly so 36. S. houstonii. 



Branches copiously pubescent, the indument variable in character. 

 Prickles of the stems large, few, mostly 3 to 6 mm. long. 

 Leaves cuneate-decurrent at base, sessile or nearly so. 



37. S. jamaicense. 

 Leaves not cuneate-decurrent at base, petiolate. 

 Leaves green beneath, sparsely stellate-hirsute. 



38. S. donnell-smithii. 



Leaves whitish-tomentose beneath 39. S. amictum. 



Prickles of the stems small, numerous, most of them 2 mm. long 



or less 40. S. lanceifolium. 



DD. Prickles straight or only slightly curved, or sometimes wanting, rarely 

 recurved but the leaves then prickly on the upper surface. 

 Fruit densely hirsute. 



Prickles of the stem glandular-puberulent 41. S. hirtum. 



Prickles not glandular-puberulent 42. S. tequilense. 



Fruit glabrous or nearly so. 



Pubescence of the upper surface of the leaves chiefly of long simple hairs. 



Calyx and pedicels not prickly 43. S. mammosum. 



Calyx and pedicels prickly. 

 Leaves sparsely hirsute on the upper surface, with few scattered 



stellate hairs beneath 44. S. aculeatissimum. 



Leaves densely pilose above, densely stellate-pubescent beneath. 



35. S. chloropetalum. 

 Pubescence of the upper surface of the leaves chiefly of fine stellate hairs. 

 Calyx accrescent after anthesis, usually closely investing the fruit 

 and nearly or quite equaling it. 



Leaves all entire 46. S. hindsianum. 



Leaves, at least most of them, undulate or lobate. 



Shorter anthers 1.5 cm. long or more; leaves lobed nearly to 



the costa 47. S. azureum. 



Shorter anthers 1 cm. long or less ; leaves usually shallowly 

 lobate 48. S. amazonium. 



