Verrucaria juglandis

Verrucaria juglandis is a species of corticolous (bark-dwelling) crustose lichen in the family Verrucariaceae.^[1] It was described in 2016 from material collected on Persian walnut roots along a riverbank in Armenia, where it grows in a unique riparian habitat. The species is characterised by its narrow ascospores and distinctive half-cap covering over its fruiting bodies, distinguishing it from related rock-dwelling species.

Verrucaria juglandis was described as new to science in 2016 by Arsen Gasparyan and André Aptroot. The type was collected from the roots of Persian walnut (Juglans regia) on a river bank near Yeghegis, Shatin (Vayots Dzor, Armenia) at about 1,600 m elevation on 23 June 2015; the holotype is deposited in B. The species keys to the corticolous/lignicolous group of Verrucaria but differs from similar taxa by its narrow, 20–23 × 6–8 μm ascospores and a thin, dimidiate involucrellum (a dark cap covering only the upper half of each perithecium). It can be separated from rock-dwelling lookalikes such as V. riparia, V. aethiobola, and V. nigrescens by a combination of hamathecium iodine reactions, perithecium immersion, and consistently narrower spores.^[2]

The lichen forms a dull, dark-brown crust (crustose thallus) that breaks into small plates (areoles), usually less than 0.2 mm thick and occupying patches up to about 2 cm across. A thin, black, branching prothallus threads between the areoles. Vegetative propagules are absent. The fruiting bodies are abundant, small, half-globes (perithecia) that emerge slightly from the thallus and measure about 0.2–0.3 mm in diameter; each has a thin, black involucrellum that covers only the upper half of the perithecium, and a tiny, depressed pore (ostiole) at the top. Internal tissues show an iodine-positive (I+) red-brown reaction in the hamathecium (the gelatinous tissue between the spore sacs). Asci are clavate with eight colourless, narrowly ellipsoid ascospores per ascus, 20–23 × 6–8 μm, lacking a distinct outer sheath (perispore). No pycnidia were seen, and spot tests are negative (thallus K−, C−, UV−).^[2]

Verrucaria juglandis is corticolous: it grows on exposed roots of Juglans regia along the Yeghegis River in riparian forest in Armenia. The roots sit more than a metre above the usual waterline but likely receive splash during heavy rain, creating conditions that also favour many rock-dwelling lichens; at the type site V. juglandis occurs among typically saxicolous species such as Athallia holocarpa, Candelariella aurella, Circinaria calcarea, members of the Myriolecis dispersa group, and Protoparmeliopsis muralis. Within a genus dominated by rock-inhabiting species, bark- or wood-dwelling Verrucaria remain uncommon worldwide, and V. juglandis is so far known only from this Armenian riparian setting; additional collections reported are from the same locality.^[2][3]

• List of Verrucaria species