Californian burr is a stout, erect, single stem or many branched annual plant with large leaves similar to those on grapes. They can grow up to 2 m high. California burr, Noogoora burr, Italian cockleburr and South American share this description. However, there is extensive variation between these species, especially in the number and length of the burrs and the spines on the burrs.
Plants tend to be single stemmed when growing in dense patches. Isolated plants have branched and spreading stems. Stems are green to reddish-brown with a rough surface.
Grapevine-like leaves grow alternately on the stems. Their shape is ovate to triangular, cut in 3 lobes. Both surfaces are green and rough textured.
The main way of distinguishing between Xanthium burr species is by the burr shape and size. The fruit or burr of the Californian burr is hard and woody, 15-25 mm long, more or less egg-shaped. It is densely covered with hooked spines 2-4 mm long and ending in longer terminal spines (or beaks) 4-6 mm long that curve inwards at the tips. The burr turns brown when mature.