Gyalideopsis wesselsii is a species of corticolous (bark-dwelling) crustose lichen in the family Gomphillaceae. The pale greenish-grey lichen forms thin, shiny crusts with a warty surface on bark and rotting logs in cloud forest environments, and is known only from two locations in Costa Rica at elevations between . It can be distinguished from closely related species by its tiny, narrowly spoon-shaped reproductive structures, dark greyish-brown fruiting bodies with triangular projections when young, and by producing a single large spore per spore sac rather than two smaller spores, as in the related G. aequatoriana from Ecuador and G. subaequatoriana from Florida.
Gyalideopsis wesselsii was described in 2006 by the lichenologists Robert Lücking, Harrie Sipman, and José Luis Chaves. The species is named in honour of Wim Wessels, a Dutch ambassador to Costa Rica who helped secure funding for Instituto Nacional de Biodiversidad's activities from the Dutch government.
The species belongs to the genus Gyalideopsis within the family Gomphillaceae, order Graphidales. It closely resembles G. aequatoriana (described from Ecuador) in its warty thallus and tiny, narrowly spoon-shaped reproductive structures (). However, G. aequatoriana differs in having larger, light brown fruiting bodies with pale margins, and producing two spores per spore sac rather than the single spore found in G. wesselsii. Another related species, G. palmata, found in the same localities, has differently shaped reproductive structures that are broadly flattened and dissected like the fingers of a hand.
Gyalideopsis wesselsii forms a thin, crustose (crust-like) thallus on bark. The thallus is continuous, measuring 10âÂÂ30 mm across and only 10âÂÂ20 üm thick, with a outer layer. Its surface is irregularly warty () due to clusters of calcium oxalate crystals. The lichen is pale greenish-grey in colour and has a shiny () appearance. The photosynthetic partner () consists of green algae ( in form) with cells measuring 5âÂÂ8 üm in diameter.
The reproductive structures (apothecia) are flattened against the surface (), in form (cup-like with a of fungal tissue), round, and measure 0.15âÂÂ0.25 mm in diameter and 60âÂÂ80 üm in height. The is flat and dark greyish brown. The margin is distinct, of the same colour as the disc, and when young is covered by 3âÂÂ5 triangular, thin, pale grey projections ().
The spore-producing layer (hymenium) is 50âÂÂ60 üm high, colourless to pale sordid green. The spore sacs (asci) are broadly club-shaped, measuring 45âÂÂ55 by 20âÂÂ25 üm. Each ascus produces a single, ellipsoid spore that is (divided by both longitudinal and transverse walls), with slight constrictions at the dividing walls. The spores measure 40âÂÂ50 by 15âÂÂ20 üm, are 2.5âÂÂ3 times as long as broad, and are colourless.
The specialized asexual reproductive structures (hyphophores) are shortly bristle-shaped with a widened, spoon-shaped () apex, measuring 0.06âÂÂ0.08 mm high and 25âÂÂ35 üm thick above the base. They are blackish brown with a pale base. The (specialized hyphae inserted at the apex of hyphophores) are branched throughout, resembling a string of beads (), with colourless, broadly club-shaped to drop-shaped segments measuring 3âÂÂ8 by 2âÂÂ3 üm.
Gyalideopsis subaequatoriana is a closely related species from Florida, USA, that serves as an intermediate form between G. wesselsii and G. aequatoriana. While sharing a similar thallus appearance and apothecial morphology with G. wesselsii, it can be readily distinguished by its significantly larger hyphophores (0.2âÂÂ0.3 mm tall) with fan-shaped, greyish-black apices compared to the much smaller, spoon-shaped hyphophores of G. wesselsii. Additionally, G. subaequatoriana typically produces two smaller spores (20âÂÂ30 by 12âÂÂ16 üm) per spore sac rather than the single, larger spores of G. wesselsii, and inhabits coastal sand pine-oak scrub ecosystems in Florida rather than the montane environments of Costa Rica.
Gyalideopsis wesselsii is currently known only from Costa Rica, where it has been collected from several locations:
The species inhabits lower montane cloud forest zones at elevations ranging from above sea level. It has been found growing on wet, rotting logs and on wood (fence posts) in exposed areas along pastures. These habitats suggest the species prefers humid environments at the edge of forested areas, particularly in the montane regions of Costa Rica. The species' occurrence in both the Cordillera de Tilarán and the Talamanca Ridge indicates it may be more widely distributed throughout suitable habitats in Costa Rica. G. wesselsii is one of 27 Gyalideopsis species that have been reported from Costa Rica.