THE YUCCEAE. 65 



^eastern Y. filamentosa and Y. flaccida , to both of which it 

 bears some relationship, while apparently distinct from 

 either. At Dallas, where Mr. Reverchon has long culti- 

 vated this and Y. rupicola , spontaneous hybrids occur, with 

 the leaf -margin neither denticulate nor filiferous. 



11. Leaves not flliferous, with a distinct thin horny, finely denticulate 

 border. 



2. Capsule mucronate, with flat-backed valves. 



Y. rigida (Engelmann) Trelease. 



r. rupicola rigida Engelmann, Trans. Acad. St. Louis. 8 : 49. (1873). 

 Watson, Proc. Amer. Acad. 14 : 253. Baker, Journ. Linn. Soc. 

 Bot. 18 : 223. 



Caulescent, reaching a height of 3 to 5 m., simple or elongately few- 

 branched above. Leaves glaucous, thin but rather rigidly spreading, 

 about 25 mm. wide, mostly concave, often with scabrid ridges, slender- 

 tipped but very pungent, the yellow margin minutely denticulale. Inflo- 

 rescence rather large, panicled close to the branches, glabrous. Flowers 

 not very large. Capsule oblong, thick-walled, rough, not constricted, 

 the flat valves tipped with short outcurved points : seeds very dull, 4 to 5 

 X 6 to 6 mm. Plates 35. 36, f. 1. 84,f.l. 



Mexico, from central Chihuahua to eastern Durango. 

 Plate 93, f. 2. 



The Engelmann herbarium contains two specimens (nos. 

 A. and 477) of a Yucca collected in 1847 by Dr. Gregg, in 

 a dry valley between Mapimi and Guajuquilla, in northern 

 Mexico, which he noted as from 5 to 10 feet high, and which 

 possesses glaucous denticulate-margined rather narrow 

 leaves which in the herbarium appear quite rigid. In 

 revising the Yuccas, Dr. Engelmann, recognizing a certain 

 comparability of these specimens with Y. rupicola, desig- 

 nated them by the varietal name rigida, under that species, 

 evidently mistaking Gregg's note on the height of the 

 plants for that of the scape, instead of the trunk, which 

 it really appears to have referred to. Within recent years, 

 the same plant has been collected (and sometimes referred 

 to this variety) by Wilkinson (134715, 224209), Rae and 

 Hough (4220), and Pringle (165) in the Santa Eulalia 

 mountains, near the city of Chihuahua. 



5 



