The species (N. testudinaria) also recognized by the protruding reticulate vein-like ridges in the cortex as seen between branch margins, the cortex also appearing dull to slightly glossy along marginal ridges, relatively thick, 75–150 μm thick.

The key taxonomic character to recognizing N. homalea has been the obscure reticulate cortical ridges between the branch margins,[2] in which the obscurity appears related to an extra glossy layer above the normal two-layered cortex, referred to as an “epicortex”;[5] however, the more frequent development of transverse cracks also distinguishes N.

which is scarcely visible, except on Guadalupe Island where thalli have a glossy cortex with prominent transverse ridges less frequently cracked.

[2] Additional character features for distinguishing N. homalea are branches that are mostly erect and closely parallel (“fastigiate”), and are often more curved than abruptly bent near apex.

Niebla eburnea differs in its pastry like smooth cortex, and in the branches twisted near base, in contrast to the frequent twisting of the longitudinal ridges as related to a change in the orientation of the branch margins in N. testudindaria[2] William Nylander described Niebla testudinaria as a species of Ramalina (R. testudinaria) occurring on rocks (saxicolous) and branches of shrubs and trees (corticolous lichen) in California among a small group of related species that included R. ceruchis reported to occur on rocks and shrubs (and cacti) in South America (=Vermilacinia ceruchis), R. combeoides (=Vermilacinia combeoides) on rocks in North America, R. homalea (=Niebla homalea) on rocks around San Francisco, and R. flaccescens (=Vermilacinia flaccescens) on shrubs in South America.

intermedia, that had been described by Johannes Mueller Argoviensis (of Aargau) in 1882;[2] both regarded as occurring only on rocks, in contrast to the shrub thalli that were considered to belong to R. ceruchis by the teretiform branches.

Except for the taxonomic key and comments, his detailed descriptions of the species were largely extracted from Nylander's (1870) monograph.