pla eA eas te OTE ME te ee al - ee Oe a ee ee ee | a ee oer te 
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 filiferous, with a distinct thin horny, finely denticulate 
border. 
2. Capsule mucronate, with flat-backed valves. 
Y. rigida (Engelmann) Trelease. 
Y. rupicola rigida Engelmann, Trans. Acad. St. Louis. 8: 49. (1873).— 
Watson, Proc. Amer. Acad. 143 253. — 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 5to6 mm.— Plates 35. 36,f.1. 84, f. 1. 
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 
