Diagnosis. A corticolous, foliose species with narrow, shortly elongate, very minute lobes, 0.1–0.3 mm wide, apically broadened to 0.5 mm, the upper side deep yellow to deep orange, the lower surface white to pale yellow, with few cilia (marginal rhizines), attached with hapters or short, scarce rhizines, soralia pustulate-capitate, mostly apical, rarely submarginal.

Type. Ecuador, Galápagos: Isabela, Volcán Alcedo, along the trail going up the E-slope, basalt rubble field to the SE side of the trail and the barranco, 0°24′3″S, 91°2′35″W, 434 m alt., dry zone, basalt rubble field with scattered vegetation (Bursera graveolens, Zanthoxylum fagara, Pisonia floribunda, Senna pistaciifolia), on bark, 09-Mar-2006, Bungartz, F. 4417 (CDS 28502‒holotype; GenBank Accession number nrITS: MT967476).

Description. Thallus minutely foliose, forming small to medium-sized, ± coralloid rosettes or small mats of stout, sub-erect, anisotomically branched lobes; lobes dorsiventral, mostly convex, narrow, shortly elongate, 0.1–0.3 mm wide, slightly broadening at their flattened, ± truncate apex (up to 0.5 mm wide); lobe margin rarely with very few cilia (= marginal rhizines); upper surface deep yellow to deep orange, smooth, epruinose, dull to ± shiny; lower surface white to pale yellow, ± wrinkled, attached by few, sparse hapters (or short rhizines); soralia mostly apical, occasionally submarginal, pustulate-capitate, ~0.1–0.2 mm broad, with coarse, granular-blastidiate yellowish to bright orange, in parts ± greenish soredia, (24–)26–37(–40) μm in diam. Apothecia unknown. Pycnidia unknown.

Chemistry. Thallus and apothecia P–, K+ purple, C–, KC± purplish, UV– (dull); thallus and apothecia contain a large proportion of parietin, a smaller proportion of fallacinal and very small proportions of teloschistin, parietinic acid and emodin (chemosyndrome A3 sensu Søchting 1997).

Ecology and distribution. Known only from the Galapagos, where it is a relatively rare species. It is most common throughout the dry zone, occasionally also in the transition zone, rarely in the humid zone (Cerro Gavilan, Santiago). Typically, it grows on bark (often on Pisonia floribunda, less frequently on Bursera graveolens or Piscidia carthagenensis), but there are also two specimens from rock.

Etymology. The epithet leoncita means little lion in Spanish and the golden orange rosettes recall a lion’s mane; incidentally, the name is also a nickname of the first author’s daughter Lea.

Notes. Compared to other species in the genus, Xanthomendoza leoncita has unusually minute lobes, almost as small as those of Polycauliona tenuiloba (known only from the Sonoran Region). That species, however, has an overall grayish white to very pale yellow thallus, never deep yellow or orange. Although lobes of X. leoncita have the tendency to grow slightly erect, often forming small mats, its individual lobes appear more distinctly flattened and not as ‘terete’ as those of Polycauliona candelaria, which typically forms ± coralloid cushions. Habitually, X. leoncita also resembles Polycauliona adscendens, which, however, has much wider lobes with helmet-shaped tips. The species is described here as a Xanthomendoza, because specimens typically have at least some, though often only few cilia or short rhizines. Unfortunately, conidiomata were not observed, but the molecular results also suggest the species belongs in Xanthomendoza, not in Polycauliona, and seems to be closely related to X. weberi.