Xanthomendoza fallax (Hepp ex Arn.) Soechting, KSrnefelt & S. Kontratyuk.
X. fallax is classified as: Ascomycota > Pezizomycotina >Lecanoromycetes > Lecanoromycetidae > Teloschistales > Teloschistaceae > Xanthomendoza > fallax
X. fallax is characterized by the bird nest soralia, wich are formed when the upper and lower cortex split and separate. Crescent-shaped opening then explode the soredia produced from the medullary layer.
The thallus is foliose, forming small to medium sized rosettes up to 3cm wide, and sometimes coalescing. The rosettes are adnate to loosely adnate, as well as lobate. The lobes are dorsiventral, flattened to convex, 0.8-2mm wide, with tips that are truncate to rotund and 0.3-0.9mm wide. The upper surface is distinctly yellow to orange, smooth to shiny, and sorediate. The soredia are powdery, marginal in horizontal crescent-shaped slits called ‘birds nests’. The medulla are white and reticulate, with short to elongate hyphae. The lower surface is white to yellow, somewhat wrinkled, rarely with short white hapters.
The apothecia are rare, but when they occur, are laminal, stipitate, and up to 2.5mm in diameter. The margin is initially smooth, but often becomes sorediate and with cilia. The disc is orange, and the epihymenium is brown and 10um thick. The hymenium is hyaline below, 50-110um tall. The paraphyses are simple or branched, cylindrical, and septate. The hypothecium is hyaline to pale brown, 30-90um thick. The asci are clavate, with 8-spored ascospores that are ellipsoid, polaricocular, hyaline, and 11.5-17c6-9um. The septum is 2-5um wide. The pycnidia are common, immersed to protruding darker than upper surface conidia, which are bacilliform, 2-3.6×1-1.5um.
Spot tests for the upper surface include K+ purple, C-, KC-, and P-. This lichen also produces secondary metabolites: parietin (major) fallacinal (major), emodin, teloschistin (major), and parietinic acid.
X. fallax occurs, like most lichen, in specific habitats: bark, rarely rock or detritus, in rather humid (never dry) microclimates. It is widespread in temperate regions around the globe. Interestingly, one can often find colonies growing on cemetery headstones.
Consortium of North American Lichen Herbaria: