Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.

Life habit: lichenized Thallus: fruticose, tufted to pendent, often caespitose, sparsely to sometimes abundantly branching, often polymorphic, occurring as mat-like, appressed cushions 2-3(-6) cm tall to larger pendulous or bush-like plants 4-8 cm long in species with flattened branches branches: diminutive and usually less than 1 mm in diam. to robust and several cm long and 1-3 mm wide, either flattened, cylindrical, subcylindrical, or cylindrical to terete, often cracked surface: varying from shiny and pale yellow to dull and nearly white or to greenish yellow and stippled with black, smooth to pustulate, often ridged or crinkled, maculate or not cortex: ranging from an anticlinal or palisade layer underlain by supportive tissue to a simpler sheath that grades into a thicker cortex medulla: white, cottony and loose to densely compact with individual hyphae occasionally adhering to each other, sometimes with increasing adhesion to form aggregates or strands (particularly when growing on rocks) and forming a central cord in N. tuberculata photobiont: primary one a Trebouxia green alga, secondary one lacking attachment: lacking when growing on soil, but otherwise with a hold-fast-like, often blackened structure Ascomata: apothecial, lateral, marginal, terminal or subterminal, generally circular in outline, solitary or in clumps, up to 2-5 mm in diam., sometimes larger disc: exposed, white, tan, or gray asci: clavate, 8-spored ascospores: hyaline, 1-septate, straight to gently curved, occasionally strongly curved, 10-14(-20) x 4-5 µm Conidiomata: pycnidial, black, solitary, immersed, c. 0.1 mm in diam. conidia: straight, rod-like, usually 4-5.5 x 1 µm Secondary metabolites: orcinol and ß-orcinol depsides, depsidones, terpenes, aliphatic acids, and usnic acid Geography: an obligate maritime group occurring from southern Alaska to Baja California Sur in North America, and in Mediterranean type ecosystems on SW Europe and the Canary Islands, coastal Chile, and South Africa Substrate: on rock, soil, and bark. Notes: Similar to Ramalina, many Niebla species are extremely plastic in morphology, and populations on rock may appear wind-trimmed and stunted at exposed sites, but become pendant at protected ones. For example, forms of N. homalea on sand are unattached, bushy, tumbleweed -like sterile morphologies, while rock populations of the same species have blades arising from a holdfast and are often fertile. Soil populations are recent, because sea levels would have covered their habitat several times within the last 10,000 years, a time length likely inadequate for species-level separation even if there were complete genetic isolation. In the shrub-inhabiting Niebla ceruchis, interior populations tend to be large and crinkled caespitose thalli with variable maculation, while those along the immediate coast have some more markedly maculate and thinner-branched forms. All morphologies intergrade. Perhaps the least variable is N. ceruchoides, a primarily saxicolous species that characteristically resembles a cushion plant or bryophyte in growth form. Taxa occurring on rocks, such as N. combeoides, N. cedrosensis, N. procera, N. polymorpha, N. laevigata and N. robusta, all are sufficiently distinct from each other to allow separation, especially if the variation in the population at a site can be examined. Henry Imshaug (personal communication) once stated: "I don't identify lichen species (based upon a single plant or collection), I identify populations of a lichen species (representing the full variability)", and that insight is profoundly appropriate for Nieblae, as well as many Ramalina species. Thus, the genus Niebla reflects the same morphological polymorphism seen in the Roccellaceae, and in many Ramalinae. Similarly, chemistry is not a basis for separating Vermilacinia from Niebla. Niebla homalea and N. josecuervoi, species with abundant ground and rock populations, have a diversity of chemical races producing depsidones and depsides with many unidentified terpenes, while many of the other Sonoran Niebla species produce depsidones (salazinic or norstictic acid) in some races, but usually the terpene (-)-16α-hydroxykaurane. Since there are no apothecial, spore, pycnidial, or conidial differences, a great variability within medullary features, great overlap in chemical pathways, and intergrading cortical designs, there is no basis for generic segregation. Just as in the genus Ramalina, Niebla embraces a range of morphologies and chemistries that do not warrant generic segregation any more than viewing rock-inhabiting, chemically rich taxa with rigid blades like Ramalina siliquosa as separate at the generic level from the pendulous, chemically depauperate, more flexible species such as Ramalina thrausta, Ramalina anceps or Ramalina menziesii. The morphological variation within the Nieblae is so rich that over seventy species have been proposed, most by Spjut in 1996, based upon cortical cracking, chemistry, and the extremes in blade morphology, size and substrate within already described taxa. According to that interpretation there are 72 North American taxa, of which 36 species and a variety are accommodated within the genus Niebla (N. josecuervoi, N. homalea and its isidiate derivative). The remaining species were placed in the genus Vermilacinia that was divided into two subgenera, the subgenus Vermilacinia (Niebla ceruchis and its closest affiliates) and subgenus Cylindricaria (Niebla combeoides and other cylindrical or subcylindrical taxa). Over fifty of the species described or accepted by Spjut for North America are not accepted here, just as Vermilacinia is rejected, because the proposed segregates are captured within the range of polymorphism in previously described taxa and for the most part recognized by previous workers. Ground and rock populations are not regarded here as distinct at a taxonomic level, nor are chemical products alone (the depsidone line of salazinic, protocetraric, hypoprotocetraric, or norstictic acids; or