Vermilacinia varicosa is a fruticose lichen known from two islands along the Pacific Coast of central Baja California, Isla San Roque located just off the southern Vizcaíno Peninsula west of Bahía Asuncón [1] and Cedros Island where found on precipitous rocks along the northwest coast.

[2] His lichen specimens had been kept separate from the mounted and filed lichen collections in the herbarium at the Smithsonian Institution, Department of Botany, US)[3] loose in brown standard herbarium paper, and were made available to Richard Spjut sometime after 1986 while he was undertaking a revision of the genus Niebla[4] Vermilacinia varicosa is classified in subgenus Vermilacinia in which it is distinguished from related species by its thallus divided into relatively few fan-shaped branches (less than 10)—widely expanded above a short narrow stalk-like base—and by its secondary metabolites of terpenoid compounds that generally characterize the subgenus: an unknown T3, the triterpene zeorin and the diterpene (-)-16 α-hydroxykaurane, with an accessory β-orcinol depsidone, salazinic acid.

Vermilacinia rosei, also collected by Rose from Isla San Roque, appears morphologically indistinguishable, differing only in chemistry of the triterpenes, which have taxonomic significance from a phytogeography point of view[4] Vermilacinia johncassadyi, for example, which has the T1 and T2 triterpenes, and is found only in the Vizcaíno Desert, is morphologically similar but geographical separated from V. laevigata, a species of the California Floristic Province that differs morphologically by stalked apothecia and chemically by the lichens substances generally found in the subgenus.

Emphasis has been given to chemical characters because they correlate with known phytogeographical and ecological differences in vascular plants as outlined in Richard Spjut’s introduction and taxonomic keys to the species.

[5] Among the species recognized by Bowler and Marsh, V. varicosa resembles V. robusta more than V. laevigata, but it would appear that the apparent flattened branch morphology is the character attribute that was given taxonomic weight.