Gray Horsebrush, Spineless Horsebrush: Tetradymia canescens (Synonym: Tetradymia inermis) - Upright, much-branched (and unarmed) shrugs to 60 cm tall. Leaves and twigs are gray tomentose, 1 to 3 cm long, linear, and upright or closely appressed to the twigs.
Little-leaf Horsebrush: Tetradymia glabrata - Upright shrubs to 80 cm in height, unarmed, with small, often glabrous, linear leaves to 1 cm in length. Conspicuous white-tomentose lines run the lengths of the twigs.
Catclaw Horsebrush, Cottonhorn Horsebrush: Tetradymia spinosa (Synonyms: Tetradymia spinosa var. longispina, Tetradymia spinosa var. spinosa) - Plants armed with claw-like spines, as in photo above.