Synonym:
Yucca baccata var. vespertina McKelvey, in Yuccas Southwest. U.S. 1: 45, 1938
Yucca vespertina (McKelvey) Welsh, S.L,  in Rhodora, 95(883-884): 417 (1993)

Type location:
Just east of Peach Spring, Arizona.

Distribution:
San Bernardino Co. California, southern Nevada, south eastern Utah and in Mohave Co. and Yavapai Co. Arizona.

Short description of the species:
Yucca baccata var. vespertina is highly variable, but are generally acaulescent or with a short prostate trunk, forming large confused clump of asymmetric rosettes. Leaves pale blue to sage-green, twisting, rigid, 50 to 75 cm long, concavo-convex, rough, with the leaf margin splitting up as fine curly fibers. Inflorescens unimpressive, small, short, scape short and slender with 10 -12  branchlets , 30-45 cm tall, flowers starts well below the leaves, and rarely exceeding those. Flowers white or cream, pendulous (bell shaped), 7 to 8 cm long Fruit fleshy, indehiscent ; Seeds are dull black, thick, and wingless.

Hardiness:
I haven't tried Yucca baccata var. vespertina yet, but would think that it can be grown in a pot which is stored dry inside a unheated greenhouse in the winter, or grown in a bed inside an unheated greenhouse, but probably not down to more than -12C at  night and above 0C during the day.

Related species in the Series Baccatae:
Yucca arizonica
Yucca baccata
Yucca baccata ssp. thornberi
Yucca baccata ssp. vespertina
Yucca confinis

Pictures:

Yucca baccata ssp. vespertina
near Peach Springs, Arizona.
Photo by Craig Howe ©2000-2005

Yucca baccata ssp. vespertina
near Peach Springs, Arizona
Photo by Craig Howe ©2000-2005

My own plants:
#1121 Yucca baccata ssp. vespertina, Arizona, Peach  Springs, 1560 m., fh 1179.57, sown 2000.

Reference:
MCKELVEY, Yucca of the southwestern USA 1:45-49 (1938)
WEBBER, Agric. Monograph U.S.D.A. 17:27-31 (1953)