Thallus corticolous, rarely saxicolous, folicolous or terricolous; placodioid leprose, i.e., developing upon a common, shared hypothallus, delimited by a byssoid arachnoid, ‘cottony’prothallus forming an irregular to ±indistinctly lobed margin, but always lacking a distinct lip, not ‘crisped’(finkii-type sensu Lendemer 2011a); surface greenish gray to bluish green, in the herbarium fading to a pale yellowish green; hypothallus well developed, loose, ‘fluffy’, ‘cottony’; rhizohyphae sparse or absent; granules ecorticate, ill-defined, mealy [(25–)60–80(–120) µm in diam., fairly even in size but often aggregating in larger clusters (up to 200 µm)], generally loosely packed, typically with abundantly protruding hyphae; photobiont green, coccoid, 6–12 μm in diam.

Spot tests and chemistry: P+ orange, K+ yellow, KC-, C-, UV- (pale); atranorin, zeorin, stictic, cryptostictic, and constictic acids.

Distribution and ecology: Cosmopolitan; widespread throughout the tropics (Flakus & Kukwa 2007, Kukwa & Flakus 2009, Flakus et al. 2011); new to Galapagos. This is the most common species throughout the archipelago, abundant in shaded and sheltered habitats of the humid highlands, less common in the transition zone, growing on a wide range of introduced and native trees and shrubs, often overgrowing bryophytes, rarely on soil or rocks and then typically close to the base of trees.

Notes: This taxon has previously been treated as Lepraria lobificans Nyl. (1873: 196) but according to Lendemer (2011a, 2013), L. lobificans Nyl. s.str. does not belong to the finkii-type. Lendemer (2013) points out that the name L. lobificans instead refers to what has previously been called L. santosii Aguello & A. Crespo (in Crespo et al. 2006: 218). The Galapagos material agrees well with the original description of L. finkii and this name is therefore used here.

L. finkii, L. aff. incana, L. achariana and L. lendemeri are morphologically very similar; they all belong to the same growth type, where granules develop upon a shared hypothallus lacking a thick weft of conspicuous rhizohyphae, with a more or less well defined, but not distinctly lobed margin (finkii-type sensu Lendemer 2011a). Lepraria finkii is by far the most common species, the others have only rarely been encountered. Chemically the species are well distinguished by their spot tests and UV reactions. Lepraria achariana reacts distinctly KC+ red and C+ red due to the presence of lecanoric acid, L. finkii reacts P+ orange and K+ yellow due to stictic acid; both lack distinct UV fluorescence, whereas L. aff. incana is K-, P- and fluoresces bright yellowish white under UV light (divaricatic acid). Lepraria lendemeri is also K- and P-, but displays a rather dull, dark yellow to ochraceous UV reaction (possibly caused by the presence of 4,5-dichlorolichexanthone).

Morphological differences between these species are not conspicuous. Lepraria finkii forms perhaps the most clearly delimited thalli, often appearing almost lobed. It is also the species with the best developed, thickest hypothallus, which generally appears very loose, ‘fluffy’or ‘cottony’.

The tendency to almost form lobes was not observed in either L. aff. incana, L. lendemeri or L. achariana, although L. aff. incana often forms thalli extremely similar to those of L. finkii. Thalli of L. lendemeri and L. achariana generally have smaller, powdery, more ‘farinose’ granules (though they do not form a fine dust, as does the leprose Chrysothrix xanthina). Granules of L. finkiiand L. aff. incana are generally larger, of a more mealy appearance, often also more distinctly clustered (though not as coarse as the compact pseudocorticate granules of L. vouauxii, which belongs to a different growth type).

Of all species that belong to the finkii-type, L. achariana has the least developed, thin hypothallus. According to Flakus & Kukwa (2007) its thallus is stratified, often with unidentified anthraquinones present where hyphae adhere to the substrate. This has, however, not been observed in the single specimen collected in Galapagos.

All species have a ±bluish green tinge when fresh, although L. achariana appears more grayish, fading to whitish beige, whereas the other species appear more greenish, fading to a faintly yellow, but color perception is subjective and cannot be regarded a definitive character.