Asexually formed seeds are predominant in the spring and fall, while sexually produced seed are more frequent in the summer. Rollins has divided the genus into four groups of species based on plant morphology. In this scheme, guayule is most closely related to the species P. rollinsianum . Native stands of guayule have been divided into three groups according to leaf shape, tricome morphology, and rubber content. Introgresssion from P. incanum , a species that grows in close association with guayule in natural stands, may be responsible for many of the morphological and biochemical differences among native populations.
Leaves can be oblanceolate, narrow elliptic, or ovate.
Inflorescences can range from 5 to 22 cm with 1 to 4 branches. 2,000 m. Stands are limited to outwash fans and rocky slopes of calcareous soils. For commercial production, fields should be well-drained very fine sandy loams to silty loams. While guayule can be grown with minimal irrigation, maximum yields occur when irrigation amounts are similar to other crops grown in arid regions. Guayule is susceptible to several insect and disease pathogens.