956 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



39. ANCISTROCACTUS Britt. & Rose, Cactaceae 4: 3. 1923. 



Small, globular or short-cylindric plants, indistinctly ribbed, strongly tu- 

 bercled, very spiny, one of the central spines always hooked ; flowering 

 tubercles more or less grooved on the upper side ; flowers rather small, short, 

 funnelform, borne at the top of the plant ; ovary small, bearing a few 

 thin scales, these always naked in their axils; fruit oblong, greenish, juicy, 

 thin-celled, usually naked below but with a few broad cordate thin-mar- 

 gined scales above; seeds globular, rather large, brownish to black. 



One other species occurs in Texas. 

 Radial spines 20 or more, strongly appressed, pectinate; flowering areoles 



naked 1. A. megarhizus. 



Radial spines 19 or fewer, more or less spreading, hardly pectinate; flower- 

 ing areoles woolly 2. A. scheeri. 



1. Ancistrocactus megarhizus (Rose) Britt. & Rose. Cactaceae 4: 4. 1923. 

 Echinocactus megarhizus Rose, Contr. U. S. Nat. Herb. 12: 290. 1909. 

 Type from Victoria, Tamaulipas. 



Solitary or in clusters of 3 or 4 ; plant body nearly globular or a little elon- 

 gate, 5 to 8 cm. high, usually solitary, from large fleshy roots ; ribs spiral, 

 divided into dark green tubercles, 4 to 5 cm. high ; radial spines 20 or more, 

 pectinate, at first pale yellow, in age white ; in seedlings the spines pubescent ; 

 central spines usually 4, the 3 upper similar to the radials, although a little 

 stouter, the lower central spines stout and strongly hooked, 15 mm. long ; fruit 

 green, suggesting that of a Coryphantha, clavate, bearing a few naked scales 

 near the top ; seeds black, smooth, shining. 



2. Ancistrocactus scheeri (Salm-Dyck) Britt. & Rose, Cactaceae 4: 4. 1923. 

 Echinocactus scheeri Salm-Dyck, Cact. Hort. Dyck. 1849. 15.5. 1850. 

 Northern Mexico. Texas. 



Globular to clavate, 3.5 to 5 cm. long; ribs usually 13, indistinct, somewhat 

 spiraled, strongly divided into stout terete tubercles grooved only to the mid- 

 dle; radial spines 15 to 18, spreading, 12 mm. long or less, white to straw- 

 colored ; central spines 3 or 4, the lowest strongly hooked ; flowers 2.5 cm. long, 

 greenish yellow; ovary small, nearly naked; seeds large (about 2 mm. long), 

 brown and minutely tuberculate (according to Coulter). 



40. THELOCACTUS Britt. & Rose, Bull. Torrey Club 49: 251. 1922. 



Plants of medium size, globular or somewhat depressed, spiny, often densely 

 so ; ribs few, low or even indistinct, often spiraled, divided into large tubercles ; 

 flowering tubercles more or less grooved above ; flowers from near the center 

 of the plant, borne on very young tubercles, rather large, campanulate, di- 

 urnal ; scales on ovary usually few, their axils naked ; fruit, so far as. known, 

 dry, dehiscing by a basal pore ; seeds numerous, black, finely tuberculate, with 

 a large basal hilum. 



The species here listed are the only ones known. 

 Ribs indefinite, strongly tubercled. 



Spines partly curved outward 5. T. buekii. 



Spines all straight. 

 Tubercles not flattened laterally; radial spines 6 to 9. 



1. T. hexaedrophorus. 

 Tubercles flattened laterally; radial spines 1 to 5. 



Flowers white 2. T. rinconensis. 



Flowers not white. 



Flowers salmon to yellow 3. T. lophothele. 



Flowers rose-purple 4. T. phymatothele. 



