Type: United States of America. Florida: Collier County, Fakahatchee Strand State Preserve, 5 km NW of Copeland, 26°00’N,
81°20’W, sine dato, Thor, G. 4643b (S–holotype).

Description. Thallus corticolous or lignicolous, moderately thickened, continuous to verruculose; surface pale yellowish green to yellowish gray, smooth epruinose, sorediate, soralia yellowish to greenish white, generally brighter in color than the thallus, pustulate, convex to coalescent in old thalli often covering and obscuring almost the entire thallus surface, soredia mealy to ±granular; prothallus a compacted, blackish brown line, occasionally indistinct. Apothecia often absent or sparse, circular in outline, 0.4–1.0 mm in diam., sessile, distinctly lecanorine with a smooth, epruinose margin concolorous with the thallus and with age often disintegrating into soredia; disc plane to slightly concave, orange brown to deep olive brown, rarely almost blackened, epruinose to indistinctly pruinose; hymenium hyaline, not inspersed, epihymenium with a weak, diffuse orange-brown pigment (cf. elachista-brown: dissolving in K, HCl± dull greenish brown, N−; adding K after N causes the formation of ca. 1 μm fuscous brown granules), both pigment and crystals soluble in K (chlarotera-type) [however: in Galapagos at least some apothecia additionally have discs discolored by an aeruginose pigment in part of their epihymenium (cinereorufa-green: intensifying in K, HCl+ bluish green, N+ reddish violet); pigment not dissolving in K (gangaleoides-type)]; proper exciple thin, indistinct, with few crystals; thalline exciple thick, ecorticate to indistinctly corticate, with large crystals insoluble in K (pulicaris-type); hypothecium hyaline; ascospores 8/ascus, simple, narrowly to broadly ellipsoid (occasionally with ±tapered ends), (8.9−)10.1−12.2(−12.9) × (4.0−)4.5−5.9(−6.9) μm (n = 25). Pycnidia not seen.

Chemistry. Thallus cortex, soredia and apothecial margin K− (dirty brownish yellow), rarely K+ yellow (if with atranorin), C–, KC− (dirty brownish yellow), P−, rarely P+ yellow (if with atranorin), UV−; containing usnic acid and unidentified triterpenoids; Guderley (1999) also reported atranorin and chloroatranorin, neither are present in any of the Galapagos specimens examined [specimens examined with TLC: Aptroot, A. 63741 (CDS 30299), 64786 (CDS 31361); Bungartz, F. 3937 (CDS 27819), 6474 (CDS 34691), 7077 (CDS 37558); Weber, W.A. s.n. (L-40161, COLO 189964); Yánez-Ayabaca, A. 1794 (CDS 48077)].

Ecology and distribution. A tropical-subtropical species, originally described from Florida (USA), but also reported from Mexico, the Caribbean and the Galapagos (Guderley 1999); from the coastal to the humid zone, most frequent in the dry zone, a common epiphyte, frequently also on wood.

Notes. The taxonomic status of the Galapagos representatives of this species does not appear to be well resolved. Not only are the Galapagos specimens unusual in lacking atranorin, but they are often characterized by the presence of an aeruginose, N+ purple pigment in the epihymenium. Specimens lacking atranorin were previously mentioned by Guderley (1999), but he did not observe the aeruginose pigment in L. floridula. The pigment concentration occasionally seems to be very low and in some specimens it cannot be detected.
The newly described saxicolous L. malagae (see below) closely resembles L. floridula, as both have pale greenish soredia. Lecanora malagae always has a distinctly darkened epihymenium, strongly colored by an aeruginose, N+ purple pigment. The two species are clearly distinguished by their exciple anatomy and alternative chemistry: the exciple of L. malagae lacks large crystals and specimens always contain atranorin in addition to usnic acid. Morphologically both species closely resemble L. jamesii J.R. Laundon. However, L. jamesii differs in containing 3,5-dichloro-4-O-demethylplanaic acid and in lacking terpenes. It is not known from the archipelago.