The species is identified by small oval hairy succulent leaves.

[3] The species was first described by William Jackson Hooker and George A. Walker Arnott in 1832 as Hosackia tomentosa.

[4] As of October 2024[update], Plants of the World Online accepted two varieties:[1] A. tomentosus var.

glabriusculus has the synonym Acmispon heermannii, and has been known by the common name Heermann's bird's-foot trefoil.

[5] As of October 2024[update], Plants of the World Online and the Jepson eFlora accept this variety rather than the species A. heermannii.