STANDLEY — TREES AND SHRUBS OF MEXICO. 109 



FF. Leaves gray or lightly blue-glaucous. 

 Leaves numerous. 



Leaves somewhat rough — 25. A. kirchneriana. 



Leaves smooth. 



Plant subacaulescent. 

 Teeth gradually tapered. 

 Teeth short. 



Leaves lax 26. A. pacifica. 



Leaves more rigidly ascending. 



Teeth distant (2 to 3 cm. apart) 27. A. cantala. 



Teeth closer (1 to 1.5 cm. apart) -_28. A. tequilana. 

 Teeth long and strong. 



Teeth sharply flexed 29. A. pseudotequilana. 



Teeth gently curved 30. A. sullivani. 



Teeth abruptly slender-cusped 31. A. ixtli. 



Plant distinctly caulescent 32. A. fourcroydes. 



Leaves few. 



Spine grooved only at base 33. A. datylio. 



Spine grooved to middle 34. A. vexans. 



FFF. Leaves very white-glaucous. 



Leaves very long and concave 35. A. nivea. 



Leaves shorter, rather dagger-like. 

 Leaves not falcate. 



Teeth gradually pointed 16. A. collina. 



Teeth deltoid at base 37. A. macroacantha. 



Leaves falcate 38. A. yaquiana. 



CC. Marginal teeth few or minute. 



Leaves oblong, green, transiently glaucous 23. A. sisalana. 



Leaves oblanceolate, pale 39. A. desmetiana. 



BB. Leaves hard-fibrous, oblanceolate-oblong. 



Teeth small and slender. Spine needle-shaped 40. A. thomasae. 



Teeth conspicuous and strong. 



Leaves relatively long (nearly 1 meter). 

 Spine needle-shaped. 



Spine involute 41. A. deamiana. 



Spine round-grooved ^ _• 45, A. kellermaniana. 



Spine conical, flat-grooved 42. A. hurteri. 



Leaves short (scarcely 0.5 meter long). 



G. Spine conical, flat-grooved or shallow-gi'ooved. 



Spine brown, much twisted 43. A. tortispina. 



Spine gray, straight 44. A. pachycentra. 



GG. Spine round-grooved. 

 Teeth close together (10 to 15 mm. apart) chestnut. 



Teeth slender-cusped 45. A. kellermaniana. 



Teeth heavily triangular 46. A. samalana. 



Teeth more separated, red-brown 47. A. lagunae. 



GGG. Spine involute at base. 



Teeth easily detachable .- 48. A. minarum. 



Teeth firmly attached. 



Teeth small 49. A. seemanniana. 



Teeth large, brown. 



Spine needle-shaped ; teeth almost hooked 50. A. tenuispina. 



Spine conical; teetli nearly straight 51. A. opacidens. 



