Description: This small Bacidia with a pale green, granular thallus requires the use of a microscope for certain identification. It is a species of damp calcareous rocks which has a thallus that on warm, sunny days seems to become almost invisible. The whitish to brown discs with a thick margin have a dark reddish brown, upper hypothecium. Spores, needle-like, > 25&

371;m long, conidia curved but never hooked like the top of a walking stick. Rather frequent in some urban habitats. In Ireland, very few records: North midlands and north-west.

Key Identification Features:

• Thallus granular, green or buff, with white to red-brown discs on damp calc rock
• Upper hypothecium reddish, spores > 25ųm long and conidia not hooked.

Original text submitted by Vince J. Giavarini

Distribution Map from NBN: Bacidina arnoldiana at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Bacidina arnoldiana at iNaturalist World Species Observations database.