Gyalectidium membranaceum is a species of lichen-forming fungus in the family Gomphillaceae. It is a tiny, foliicolous (leaf-dwelling) lichen known only from cloud forest on the island of La Palma in the Canary Islands. The species is distinguished by its unusual bluish, membrane-like reproductive structures, and no sexual fruiting bodies have been observed.
Gyalectidium membranaceum was described as a new species in 2001 by Emmanuël Sérusiaux and Robert Lücking. In the original account, it was characterized by its thin, meagre thallus and by (asexual reproductive structures) reduced to a bluish, membrane-like layer that covers a mass of conidial spores (diahyphae).
The species was compared with Gyalectidium imperfectum, which also has hyphophores reduced to adnate spots. G. membranaceum differs by having much thinner, more membrane-like hyphophores and a thallus that is distinctly cracked into small patches () rather than finely warty (). The authors suggested that the membranaceous layer together with the diahyphal mass functions as a single dispersal unit, since many thalli have strongly scalloped () margins where these structures appear to have been removed as a whole.
The thallus forms very small, rounded to crenate, rather ill-developed patches about 0.05âÂÂ0.1 mm in diameter. It is indistinctly areolate, with a whitish, flattened crystalline cluster at the centre surrounded by a thin greenish-grey marginal zone.
The hyphophores are located at the thallus margins but lack the scale-like covering typical of the genus. Instead, each is reduced to a small spot of spore-producing tissue (the diahyphal mass), covered by a thin, pale bluish-grey membrane about 0.07âÂÂ0.1 mm in diameter. Apothecia and pycnidia have not been reported for this species.
Gyalectidium membranaceum is known only from the island of La Palma (Canary Islands). The type locality was described as a remnant of evergreen, subtropical cloud forest, and the species was reported as very rare there, found on only a few leaves.
In that locality it was observed as a pioneer on young leaves of Lauraceae, occurring together with Gyalectidium colchicum.