Toad Lichen

Melanohalea exasperata

Description:

Foliose lichen. The thallus is olive green to brown and shiny. The thallus ranges in size from 2 cm to 10 cm. The thallus divides into small lobes (1 mm to 5 mm wide) which expand towards the tips to end rounded. One of the most characteristic features of this lichen is the warty surface. The common name of Toad Lichen describes this warty texture and olive green colour. The warts look like tiny volcanoes under a hand lens; each has a conical shape with a ‘mouth’. The warts extend to the apothecia. Apothecia are common in this species; the disc surface is concave or flat. The under surface is dark brown, becoming buff towards the edges. The rhizines are simple. Spores are colourless, one celled and 8 to an ascus. The papillae warts are evenly distributed around the rim of the lecanorine apothecia. Photobiont is the green algae Trebouxia.

Habitat:

They like an acid environment and so are usually found on coniferous trees, but they will grow on birch, willow, alder and oak. They are rare on rock substrates. This one was spotted on the bark of a horse chestnut tree