Acaena pinnatifida is a species of flowering plant in the family Rosaceae. It is known by the common names Argentinian biddy-biddy and California sheepbur. It grows in California (United States), Argentina and Chile. The population from California is sometimes considered to be a distinct species or variety from the population in South America.

Distribution and habitat: Acaena pinnatifida is known from California (in the United States), and in South America (Chile to Argentina). In North America, the species grows on roadsides, sand dunes, rocky slopes and coastal grasslands.

Taxonomy: Acaena pinnatifida was first formally named and described in 1798 by Hipólito Ruiz López and José Antonio Pavón (Spanish botanists) in the Flora Peruviana, et Chilensis journal.

Etymology: In English, Acaena pinnatifida is commonly known as the Argentinian biddy-biddy and as the California sheepbur.

Varieties: Acaena pinnatifida is often discussed as consisting of distinct varieties. These include the following:

• Acaeana pinnatifida var. californica, which is endemic to coastal scrub areas and open rocky slopes in California. It is a perennial herb that flowers between March and May. It can be found at elevations ranging from . This variety has also been treated by some authorities as a distinct species (Acaena californica).