A new species of Homalothecium from California is described and illustrated. This species was first recognized as distinctive during analysis of a DNA investigation into members of Homalothecium and related genera. Homalothecium californicum sp. nov. is distinct in its frondose branching, patent to loosely erect leaves, size intermediate between the somewhat similar H. megaptilum and H. nevadense, and cylindrical, straight, and orthotropous capsules with basally reddened exostome teeth. Subsequent herbarium and field exploration determined this new species to be a rather common and widespread species in central and northern California within a mixed conifer-hardwood transition zone. Several herbarium collections of this new species were found previously determined as Homalothecium megaptilum, H. nevadense, H. fulgescens or H. aeneum.