Vandenboomia is a small genus of lichen-forming fungi in the family Ramalinaceae. It has two species. The genus was circumscribed by the Ukrainian lichenologist Sergey Kondratyuk in 2019, with V. chlorotiza assigned as the type species. The genus name honours the Dutch lichenologist Pieter P. G. Van den Boom.
Vandenboomia species are characterised by their reproductive structures, which include both sexual (apothecia) and asexual (pycnidia) forms. The apothecia, which are small cup-like fungal fruiting bodies, measure between 0.1 and 0.3 mm in diameter. These structures are partially sunken into the lichen surface or sitting slightly above it, and appear somewhat rounded and convex, sometimes with a bumpy surface. They are coloured either bright pink or display a mottled brownish pattern. The apothecia lack the typical rim of algal cells (known as a ) that is common in many other lichens.
Inside the apothecia, the spore-producing layer (hymenium) is 25 to 40 üm tall. The spores produced in these structures (ascospores) are elongated, measuring between 9 and 18 üm long (most commonly 10âÂÂ12) and 2âÂÂ3 üm wide, and may be either undivided or split into two cells by a central septum.
The genus also produces two different types of asexual reproductive structures (pycnidia). The smaller type measures up to 50 üm in diameter and produces curved or hook-shaped microscopic spores (microconidia) that are 7âÂÂ10 üm long and 0.5 üm wide. The larger type ranges from 70 to 160 üm in diameter, has pale, open pores, and produces straight, cylinder-shaped spores (macroconidia) measuring 3âÂÂ6 üm long and 1âÂÂ2 üm wide.
The genus Vandenboomia is found in sheltered locations, particularly in woodland areas and near water bodies. These lichens show a preference for heavily shaded environments, typically growing on bark with a basic pH. They are especially common on elm (Ulmus), ash (Fraxinus), and willow (Salix) trees, and can often be found inside tree hollows.
The genus comprises two rare species with limited geographical ranges. Vandenboomia chlorotiza is found in Atlantic regions of Europe, with documented occurrences in England, France, Denmark, and Norway. The second species, V. falcata, is known only from the Canary Islands, a Spanish archipelago off the coast of North Africa.