ON THE CLASSIFICATION OF ASCLEPIADS. 237 
Collected near Gregory, Texas, 1894, by A. A. Heller. 
Species most distinct from P. longicornu, for which Mr. Heller 
mistook it, not so much in floral structure as in the thin 
membranaceous broad foliage, and the few umbels, these 
being near the summit of the stem, though none are termi- 
nal. The foliage in all other species known is decidedly 
thick and subcoriaceous or half succulent: 
4. P. NvcrAGINIFOLIUM. Asclepias nyctaginifolia, Gray, 
Proc. Am. Acad. xii. 69 (1876). Common species of western 
and southern Arizona and adjacent southeastern California ; 
easily distinguished from all other species by its stout thick 
not at all elongated hoods, their solid part not narrowed, 
but covering the column. In structure of hood this is near 
the genus Otaria ; but in Otaria the habit and inflorescence 
are precisely those of Asclepias,and the character of the 
anther-wing is also just that of all Asclepias; but this organ 
in P. nyctaginifolium is, as in P. Lindheimeri, semiovate, 
though with this difference, that the notch is here decidedly 
below the middle. 
The succeeding species, all new, are as a group quite alike 
in having flowers of at most only half the size of those of all 
the foregoing. 
5. P.Ewonvr. Herbage ci ly sul tose: leaves 
elongated lanceolate, short-petioled : “umbels rather many- 
flowered : solid stalk of hood elongated, twice as long as the 
stamens and also thick, but narrowed under the broad and 
ample but short laminal portion: anther-wings very narrow, 
but not indistinctly angled. 
Known to me only in a single specimen, collected on the 
Mexican Boundary Survey, and preserved in the U. S. Her- 
barium, mounted upon the same sheet with one of P. nyeta- 
ginifolium and the whole labelled “Asclepias longicornu.” 
6. P.teonrnum. Decumbent stems several from the root, 
more than a foot high and rather slender for the genus: 
