San Antonio del Mar, Spjut & Marin 11185, Apr 1990	Mesa Camacho, N of Punta Canoas, Spjut 11233, Apr 1990	Arroyo Sauces, between Punta Blanca and Punta Canoas, Spjut & Marin 11438, Apr 1990
Bahía Santa María, Spjut & Marin 11559, Apr 1990	3-4 miles SW of El Rosario, windy mesa, Spjut & Marin 12662, Apr 1993	El Marrón Ridge, S of Punta Negra, Spjut 9902, May 1986
General habit on mesa southwest of El Rosario	Ridge above Punta Baja, Spjut 10261, Mar 1988	Ridge above Punta Baja, Spjut 10261, Mar 1988

Niebla effusa is perhaps the largest lichen on earth, in terms of weight and size. Thalli have been found to reach more than 1 m in diameter with a weight of more than 1 kg. An example is shown in Spjut (1996, Plate 4C) of one large thallus (held by Dr. Daniel Norris, a bryologist at the University of California at Berkeley who traveled with the author during March 1988 to Baja California). Species of Usnea, and other pendant lichens, which may drape more than 1 m from tree branches, do not produce the weight found in species of Niebla. Also, Niebla effusa attains its large size by spreading over the surface of the earth; its branches are not confined to a holdfast as in related species. Moreover, typical thalli of N. effusa often arise from bare ground between rocks, in contrast to related species arising from small stones in the same environment (photo above, Spjut 1996). Additionally, N. effusa is not a tumble (“vagrant”) lichen, one that moves about as result of being by the wind, as implied by Bowler and Marsh (2004), while other terricolous species, such as N. arenaria, may be distributed by wind at some locations. Occasional saxicolous variants of N. effusa are recognized to arise from a holdfast, or develop on rock as shown above; however, they may later spread beyond the rock (also evident in the same photo); these seem to occur more in the southern part of the species range in BCN.

Mason Hale had determined that the blackened area on the underside of the thallus of N. effusa was due to skyrin; the specimen he chose was selected by Spjut as the type (Spjut 10232A). Spjut had not said much about anthraquinones in his preparation of a manuscript (1987–1990), although he had distinguished Vermilacinia procera (formerly “V. robustiella” Spjut ined.) from V. combeoides and V. paleoderma by irregularly blackened lobes that extended well above the base of the thallus. But in this case Dr. Hale indicated that skyrin appeared to be of taxonomic value for this species (N. effsua), or for the genus, unlike other previous subtle comments about Niebla and Vermilacinia. He was making these comments while soaking specimens in water and transferring them to the press, dividing up one large thallus of N. effusa into many duplicates, some of which later became isotypes (ASU, BCMEX, COLO, DUKE, LA). As noted by Spjut (1996), the dark pigmentation at the base of the thallus is useful in some cases for distinguishing divaricatic-acid species such as N. contorta from N. undulata, or sekikaic-acid species such as N. suffnessii (not blackened at base) from N. fimbriata (blackened at base). Generally, N. effusa (salazinic acid) is blackened on the underside of the thallus, but this is also associated with contact with the substrate. A related species, N. flabellata (salazinic acid), does not have a blackened base, but it seems best distinguished by its more flattened thallus segments that appear to have irregular lacerations.

Niebla effusa is recognized not only by its terricolous habit, but also by the fringed aspect of the upper parts of dilated branches, in contrast to branchlets of a related species such as N. josecuervoi that has branchlets arising from near the base of a primary branch, often developing on just one-side in a pectinate arrangement. Although N. effusa may be frequently found to have apothecia (~66%, Spjut 1996), the apothecia are few in number per thallus in comparison to N. josecuervoi in which a thallus often has apothecia on many of the branchlets.

Niebla effusa undoubtedly constitutes much of the ground cover in terricolous Niebla communities between El Rosario and Camp Nuevo. Associated species include N. juncosa, N. josecuervoi, and N. arenaria. North of El Rosario, N. effusa may be found more with N. fimbriata instead of N. juncosa. In the Northern Vizcaíno Desert, which lies south of Campo Nuevo, the gravel “Nieblas" (Spjut 1996) fade out and rock Nieblas” (Spjut 1995, 1996) become more conspicuous, although "sand Nieblas" still occur locally on alkali earth, often appearing as single-species populations. The geographical distribution of N. effusa is similar to that shown for N. josecuervoi, a species endemic to Baja California Norte.