455 
96. Opuntia arbuscula Engelm. Syn. Cact. 309 (1856). 
Erect and arborescent, 21 to 24 dm. high, the smooth green trunk 10 
to 12.5 em, in diameter, very capitate-branching at apex (top formed 
by numerous slender divaricate branches): joints lightly tuberculate, 
the ultimate ones 5 to 7.5 cm. long, 8 mm. in diameter, with oblong- 
linear depressed (flat and indistinet) tubercles 12 mm. long: pulvini 
with white wool, and few very slender penicillate bristles: the single 
spine (or sometimes 2 side by side) porrect, at length deflexed, with 
straw-colored or yellow sheath, 18 to 25 mm. long, rarely 1 or 2 shorter 
and lower deflexed ones added: flowers greenish-yellow tinged with 
red, 3.5 em. broad: fruit ‘“bristly..—The type specimens are those of 
Schott (‘on desert heights, near Maricopa village, on the Gila”), but 
they could not be found in the Engelmann collection. 
Deserts of Southwestern Arizona and southward into Sonora. 
Specimens examined: ARIZONA (Emory of 1846; Lngelmann of 1880; 
Parry of 1881; Pringle of 1881, mesas near San Xavier Mission; Hrans 
of 1891, Tucson; Toumey of 1892, Mesa City; Wilcox of 1894, Fort 
Huachuca). 
The Evans specimen contains fruit which is clavate, strongly tuberculate and 
bristly, with funnelform wmbilicus, 2 to 2.5 em. long. It is immature, so that no 
color is indicated, and probably not the full size. This species is often confused 
with the leptocaulis forms, but its dense, stouter, almost interlocking apical branches, 
its long flat tubercles, and its yellowish sheathed spines separate it easily. There is 
great variation in spine characters, the following forms occurring: naked (spines 
probably deciduous); one spine (the common form); 2 equal spines side by side; 2 
prominent spines and 1 or 2 smaller ones; 3 or 4 spines, all alike but only 5 to 15 mm. 
long, making a short spiny-looking joint. Some of these forms might have been 
separated as varieties, but almost all of them, certainly the most diverse ones, have 
been found on different branches of the same plant. The pulvini are aptto be quite 
bristly, and the wool is oftener dirty-white than bright- white. 
97. Opuntia leptocaulis DC. Rev. Cact. 118 (1829). 
Opuntia fragilis frutescens Engelm. Pl. Lindh, 245 (1845). 
Opuntia frutescens Engelm. Wisliz. Rep. 28 (1848). 
Opuntia frutescens brevispina Engelm. Syn. Cact. 309 (1856). 
Opuntia leptocaulis brevispina Watson, Bibl. Index, 407 (1878). 
Erect and frutescent, 9 to 15 din. high, 2.5 to 3.5 em. in diameter, with 
light-gray scaly bark and erectish branches (“like pipestems”): joints 
cylindrical, 4 to 6 mm. in diameter, with indistinct tubercles 6 to 10 mm. 
long, the young joints sessile: the mostly single spine slender, 8 to 12 
mm, long, in a close sheath: flowers greenish or sulphur-yellow, 14 to 
20 mm. broad: fruit obovate, smooth, often proliferous, not tuberculate, 
deep-scarlet, fleshy, 10 to 18 mm. long: seeds few, white, compressed, 
with narrow and often acute margin, 3 mim. in diameter. (1. Pacif. R. 
Rep. iv, t. 20, f. 4, 5; also t. 24, f 16-19)—Type unknown. 
Common from northern Mexico, throughout Texas, and westward to 
Arizona; also extending to southern Mexico, 
Specimens examined: TEXAS ( Lindheimer of 1845; Wislizenus of 1847; 
