Verrucaria juglandis

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Verrucaria juglandis is a bark-dwelling crusty lichen in the Verrucariaceae family. It was described in 2016 from samples growing on the roots of Persian walnut along the Yeghegis River in Armenia, at about 1,600 meters elevation. The plant lives in a riparian habitat where the roots sit above the water and may be splashed during rain.

This lichen forms a dull dark-brown crust that breaks into small plate-like patches, usually less than 0.2 mm thick and up to about 2 cm across. A thin black prothallus runs between the plates. It does not produce vegetative propagules. The fruiting bodies (perithecia) are abundant, small, and half-globose, about 0.2–0.3 mm in diameter, sticking out slightly from the thallus. Each perithecium has a thin cap that covers only the upper half and a tiny pore at the top. Inside, the tissue between the spore sacs reacts iodine-positive (red-brown).

V. juglandis is distinguished from similar rock-dwelling Verrucaria species by its narrower spores (20–23 by 6–8 micrometers) and the half-covering involucrellum on the perithecia, along with certain chemical reactions. It is corticolous, growing on exposed walnut roots along the Yeghegis River in Armenia’s riparian forest, and so far is known only from this locality.

The species was named by Arsen Gasparyan and André Aptroot in 2016; the type was collected in 2015 near Yeghegis, Armenia, and the holotype is kept in the B herbarium.