46 



peduncle the branching of old plants is closely and repeatedly 

 divaricate. Grown plants are often finely symmetrical.* In 

 Parthenmm Lloydii, however, the branching is like that of the 

 mariola, Partheniiim incanum. The stem is more slender than 

 in P. argentatum, and the leafy peduncle is not sharply delimited. 

 Well up toward the inflorescence it bears short leafy spurs which 

 elongate after the close of the flowering season. A grown plant 

 of Parthenium Lloydii is therefore characterized by intricate 

 interweaving of the branches. In herbarium specimens the 

 striking difTerence between the two species lies in the form of 

 the leaves, which in P. argentatum are relatively only half as 

 wide as in P. Lloydii and rather deeply laciniate, whereas in P. 

 Lloydii they are typically sparsely dentate or denticulate. 



Parthenium Lloydii sp. nov. P. argentato valde similis, sed 

 ramis gracilioribus more P. incani implicatis. Foliorum major- 

 um laminae oblanceolatae, 15-18 mm. longae, 5-8 mm. latae, 

 integerrimae vel parce denticulatae, apice acutae vel obtusiuscu- 

 lae, basi in petiolum 2-3 mm. longum angustatae. Inflores- 

 centiae axis foliosus altero anno ramulifer. — Hacienda de Cedros, 

 Partido de Mazapil, Zacatecas, Mexico, F. E. Lloyd, Nos. 255 

 and 256, in Gray Herbarium. Illustrated by Lloyd, Guayule, 

 a Rubber-Plant of the Chihuahuan Desert, Carnegie Institution 

 of Washington, Publication No. 139, plates 12 and 13, 191 1. 



In the type material of P. Lloydii the pappus awns are slightly 

 incurved toward the base, but diverge at the apex. In most 

 material of P. argentatum the awns curve away from one another 

 at the base and are somewhat incurved at the apex. This 

 distinction, pointed out by Professor Lloyd, does not seem to 

 hold throughout the large series of specimens of P. argentatum 

 in the Gray and the National Herbaria, but in view of McCal- 

 lum's recent reportf that the guayule consists of as many as 125 

 segregable elementary species, the occasional inapplicability of 

 this character is not to be wondered at. The curvature of the 

 pappus may serve to distinguish P. Lloydii from certain segre- 

 gates, but not from others. 



University of Michigan, 

 Ann Arbor, Michigan 

 * Lloyd, 1. c. plate ii, fig. A. ] Science, n.s., 42: 395. 1915. 



