Calicium glaucellum
Calicium quercinum auct. p.p.
A widespread Pinhead, mainly found on lignum. Typical material has a black mazaedium (a loose spore mass, which makes sooty marks on one’s fingers if touched) on stalked apothecia with white pruina on the rim of the apothecia and an immersed thallus. The white pruina, however, can be absent, and the spores and asci need to be checked on such material. Possibly declining in the south but still frequent in the north.
Thallus usually immersed, rarely superficial, with an indistinct dark grey-green granular thallus. Apothecia 0.5–0.9 mm tall, 4–8 times as high as the width of the stalk, shiny black, usually with a faint white pruinose region at the edge and below the head, I–; head 0.23–0.34 mm diam., obovoid to lens–shaped; stalk 0.11–0.17 mm diam. Asci 34–41 × 3.5–4.5 µm, cylindrical. Ascospores 9–13 × 5–6.5 µm, uniseriately arranged, with irregular cracks and ± longitudinal ridges on the surface. Pycnidia frequent; conidia 4–5 × ca 0.8 µm, narrowly cylindrical. Thallus C–, K± dull yellow, KC–, Pd– (sekikaic, 2-O-methylsekikaic, 4-O-methylhypoprotocetraric and physodic (±) acids by TLC).
Characterised by the rather short-stalked black apothecia that frequently have a white rim of pruina on the upper part of the exciple (although this is often very sparse or absent), the immersed or rarely superficial thallus and the medium- sized ascospores that have distinctive irregular cracks and ridge fragments at maturity. Formerly often misidentified as C. abietinum, which has black-brown apothecia, lacks white pruina, a brownish shinny stem and has longer asci and larger ascospores with an irregular warty surface. Also resembles C. trabinellum. Chaenothecopsis pusilla is sometimes commensal on the thallus.
On old stumps or standing or fallen wood of coniferous and deciduous trees, more rarely on bark.
Locally common. Throughout Britain, less common in formerly sulphur dioxide polluted central and eastern areas and not obviously recovering yet; rare in Ireland.
Widespread, but the distribution data suggests a strong enough decline on the fringes of its main areas of distribution to suggest that the lichen deserves Near Threatened status. It appears to have been sensitive to sulphur dioxide and to current raised levels of ammonia in the lowlands.
Cannon, P., Prieto, M., Coppins, B., Sanderson, N., Scheidegger, C. & Simkin, J. (2021). Caliciales: Caliciaceae, including the genera Acolium, Amandinea, Buellia Calicium Diploicia, Diplotomma, Endohyalina, Monerolechia, Orcularia, Pseudothelomma, Rinodina and Tetramelas. Revisions of British and Irish Lichens 15: 1-35.
Text by Neil A Sanderson, based Cannon et al (2021)