The Lambiella caeca group of North America is a poorly known group of diminutive epiphytes with black lecideine apothecia occurring on conifer bark. We describe a new species in this group, L. arenosa, which occurs on Pinus contorta on the dunes of the Oregon coast. Both Lambiella caeca and L. arenosa share a black disk with raised, thin, persistent, often flexuose, black margins, an internally dark exciple that is thin and even, a thin, usually dark brown epithecium, and branched paraphyses that are moniliform in the upper part with K. The easiest characters to differentiate them are the smaller spores (averaging 8–11 μm long) and more conspicuous thallus of L. caeca, in contrast to somewhat larger spores (averaging over 11 μm long) and endosubstratal thallus in L. arenosa. While the known ranges of L. arenosa and L. caeca s.str. do not overlap (hyperoceanic West Coast for L. arenosa, boreal for L. caeca s.str.), a third group of specimens is problematic. Currently, we lack the data to establish whether previously sequenced members of the L. caeca group from western North America belong to L. caeca, L. arenosa, or additional undescribed species.