Allocetraria madreporiformis

Allocetraria madreporiformis, commonly known as V-fingers, is a species of fruticose lichen in the family Parmeliaceae. It forms a yellow-brown thallus of branching, somewhat inflated lobes that grow directly on the ground in arctic and high-mountain (alpine) habitats across the Northern Hemisphere. The species favours calcareous (lime-rich) soils in exposed, wind-swept sites such as ridges and arctic steppes, where wind erosion keeps mineral soil surfaces open. First described in 1810 by Erik Acharius and placed in Allocetraria in 1996, it contains usnic acid and protolichesterinic acid. Some populations are highly localised, including records from inner fjord districts of Svalbard and from glacier forefields (newly exposed ground in front of retreating glaciers) in the Austrian Alps; these occurrences have been discussed as possible results of long-distance dispersal from steppe-like areas (open, dry grass-dominated landscapes) in the Sino-Himalayan region, where Allocetraria has its highest diversity.

Taxonomy

The species was first described by Erik Acharius in 1810 as Dufourea madreporiformis, from material collected on rocks in Carinthia and Switzerland (Helvetia), which he characterized as a pale whitish, tufted thallus with short, swollen, cylindrical branches with brownish tips and no apothecia observed in the specimens he examined. Acharius also cited "Lichen madreporiformis" of Wulfen (as published by Jacquin) as a possible earlier reference, but he marked the identification as uncertain and noted that specimens sent under that name by Schleicher did not match Jacquin's figure. The binomial name Lichen madreporiformis had already been published by William Withering in 1776, so Wulfen's later use of the same name in Jacquin is treated as an illegitimate later homonym. Accordingly, modern nomenclatural sources base the accepted name on Acharius's legitimate basionym Dufourea madreporiformis. It was later transferred to Dactylina by Edward Tuckerman (1862) and to Cetraria by Johannes Müller Argoviensis (1870).