Malacothamnus lucianus is a species of flowering plant in the mallow family known by the common names Santa Lucia bushmallow and Arroyo Seco bushmallow and by the cultivar name Hanging Valley bushmallow.

It is endemic to Monterey County, California, United States, where it is known from the Santa Lucia Mountains.

lucianus but treated as a synonym of Malacothamnus palmeri var.

[3][1][4][5] Malacothamnus lucianus is distinguished from all other species in the genus by the combination of a capitate to subcapitate inflorescence and relatively long glandular trichomes.

Conversely, in Malacothamnus palmeri and Malacothamnus involucratus most rays of the stellate trichomes on the stem are less than 1 mm long and the glandular trichomes are less or equals 0.1 mm long.