44 THE CACTACEAE. 



were preserved by their authors, some have, apparently, been lost, and some, which are 

 probably preserved, we have been unable to study. 



The genus shows a great range in stem structure, varying from cylindric to broad and 

 flat. These extremes suggest different generic types, but these characters can not be used 

 except in the most general way, for some species have both rounded and flattened stems. 

 Some with round stems have flowers which suggest a closer relationship with the species 

 with flattened stems. 



The habits of some of the species are very characteristic, while others show a wide 

 range of forms. Many of the erect or tree-like forms, when grown from cuttings, develop 

 bushy habits much unlike their normal shapes. 



The spines, while somewhat constant in color in some species, vary considerably in 

 others, and the number of spines is rather inconstant. Species which are normally abun- 

 dantly spined are sometimes naked when cultivated, while species which are normally 

 naked sometimes develop spines in cultivation; cultivated specimens usually have weaker 

 spines and sometimes decidedly different ones from wild plants. 



The flowers often vary greatly in color, as is seen especially in 0. versicolor and O. 

 Hndheimeri, which show wide ranges of color forms. Some flowers vary in color during 

 the day. 



We group the species known to us into 3 subgenera, 46 series, and with the following 

 characteristics : 



KEY TO SUBGENERA AND SERIES OF OPUNTIA. 



A. Joints all terete, elongated or short, cylindric to globose. 



B. Branches several, many-jointed Subgenus i. CYUNDROPUNTIA 



C. Spines with papery sheaths. 



D. Spines, at least some of them, solitary, sometimes several, 

 acicular; ultimate branches slender, rarely more 

 than i cm. thick. 



E. Stem and branches conspicuously marked by flattened,- 

 diamond-shaped tubercles; fruit dry, covered with 



long bristle-like spines Series i. Ramosissimae (N. A.' 



EE. Tubercles not flattened nor diamond-shaped; fruit 



usually a naked berry Series 2. Leptocaules (N. A.) 



DD. Spines always more than i ; ultimate branches stouter. 



E. Ultimate branches not over 2 cm. thick Series 3. Tliurberianae (N. A.) 



EE. Ultimate branches 2 cm. thick or more. 



F. Fruit dry Series 4. Echinocarpae (N. A.) 



FF. Fruit fleshy. 



G. Tuberclesof young joints scarcely longer than broad. Series 5. Bigelovianae (N. A.) 

 GG. Tubercles distinctly longer than broad. 



H. Tubercles narrow, high, laterally flattened Series 6. Imbricatae (N. A.) 



HH. Tubercles broad, low Series 7. Fulgidae (N. A.) 



CC. Spines without sheaths. 



D. Joints not tuberculate, or with broad or flat tubercles. 

 E. Areoles long-woolly or with weak hairs (without hairs 



in 0. verschaffeltii) Series 8. Vestitae (S. A.) 



EE. Areoles neither long-woolly nor long-hairy. 



F. Joints clavate or crested Series 9. Clavarioides (S. A.) 



FF. Joints neither clavate nor crested. 



G. Low, slender species, scarcely, if at all, tuberculate. . Series 10. Salmianae (S. A.) 

 GG. Tall, stout species, the tubercles broad or flat; 



leaves large Series 1 1 . Subtilata; (S. A.) 



DD. Joints strongly tuberculate, the tubercles elevated. 



E. Tall, shrubby species; joints cylindric Series 12. Miquelianae (S. A.) 



EE. Low, prostrate species; joints clavate (transition to 



Tephrocactus) Series 13. Clavatae (N. A.) 



BB. Branches i to few-jointed, the short joints usually clustered . . . . Subgenus 2. TEPHROCACTUS (S. A.) 

 C. Joints, at least some of them, cylindric, tuberculate, the 



tubercles contiguous (transition to Cylindropuntia) Series i . Weberianae 

 CC. Joints globose to oblong, mostly little, if at all, tuberculate. 

 D. Areoles normally bearing many long white hairs, which 



often cover the whole plant Series 2. Floccosae 



DD. Areoles without hairs. 



E. Spines, when present, at least some of them, modified 



into fat, papery processes Series 3. Glomeratae 



EE. Spines, when present, all subulate or acicular, terete or 



somewhat flattened Series 4. Pentlandianae 



