Xanthisma gracile is treated here in the broad sense, to include the n = 4 Haplopappus ravenii in addition to the n = 2 and 3 chromosomal races. According to R. C. Jackson (1962, 1971), the n = 4 race can be distinguished from the other two races on the basis of floret and phyllary morphology. The former is said to possess fewer and shorter pappus bristles, shorter cypselae, and phyllaries that are covered by stiffer, more erect hairs. I have been unable to make this distinction with confidence. It is true that H. ravenii (based on specimens from its described geographic range, but not confirmed by chromosome counts) has phyllaries with often sparse, ascending to spreading hairs versus more numerous, longer, and generally appressed. Unfortunately, in surveying several hundred sheets of X. gracile in the broad sense, approximately twenty percent showed intermediacy in this character. Formal recognition of the n = 4 race has been questioned by A. Cronquist (1971) and others.
Xanthisma gracile[2] is a species of annual flowering plant in the family Asteraceae known by the common names slender goldenweed[3] and annual bristleweed.[4]
It is native the southwestern United States and northern Mexico, where it grows in the deserts and plateaus.
It is a bristly annual herb growing erect up to 45 cm tall.
The oval or oblong leaves are 1–3 cm long and divided into lobes or teeth tipped with bristles.
The inflorescence bears one or more flower heads lined with pointed, roughly hairy phyllaries. The head has a center of many yellow disc florets and a fringe of 16 to 18 yellow ray florets roughly a centimeter long. The fruit is a woolly achene 2 to 3 millimeters long tipped with a pappus.
Xanthisma gracile has extra chromosomes that do not have any functional genes (B chromosomes), and about which little is known.[4]
Xanthisma gracile is a species of annual flowering plant in the family Asteraceae known by the common names slender goldenweed and annual bristleweed.
