Calicium parvum
A medium sized Pinhead, found rarely on Pine bark on veteran Scots Pine in humid locations in both native pinewoods in the Highlands and on long naturalised Pine to the south. Similar to Calicium glaucellum, but has a prominent white-grey verrucose thallus with positive spot tests which both of which are lacking in C. glaucellum.
Thallus thin, grey to greenish grey, verrucose or ± immersed. Apothecia 0.5–0.8 mm, 6–8 times as high as the width of the stalk, black, shiny, I–, sometimes with a thin white pruina at the base of the exciple; head 0.12–0.4 mm diam., lens-shaped; stalk 80–120 µm diam. Asci clavate, persistent until the spores are nearly mature. Ascospores 8–11 × 3.5–5 µm, biseriate or fasciculately arranged, constricted at the septum and with irregular cracks on the surface. Pycnidia frequent; conidia 2–3 × 1–1.5 µm, ellipsoidal. Thallus C–, K± dull yellow, Pd+ pale yellow, UV+ white (diffractaic acid).
Resembles Calicium glaucellum, which is most usually found on wood; also distinguished from this species by the smaller apothecia, which are usually not pruinose, the superficial thallus, clavate asci, and smaller, narrower ascospores. The UV+ white and Pd+ yellow reactions of the thallus are useful for field identification, with the spot tests strongest on the larger verrucae.
On bark and sometimes wood, mostly on old Scots Pine in open humid woods, typically in glades in old growth pasture woodlands.
Rare, possibly overlooked. C. & E. Scotland in native pinewoods, and The Lake District and S. England (New Forest) on introduced Pinus.
The occurrence on Scots Pine in areas where it was introduced in the 18th century suggests it has a strong ability to colonise over long distances. Its rarity is likely determined by habitat quality limitations, rather than dispersal limitation, particularly a requirement for old well-lit Pines in humid locations. Threatened by increasing shade in its naive habitats and removal of Pines as a non-native species where it has colonised southern pasture woodland habitats. In native pinewoods grazing reductions within old growth pinewoods to allow regeneration can lead to increased shade on well-lit old trees unless care is taken. The conservation objectives for native pinewood sites need to take account of the biodiversity importance of the combination open space, dead wood and veteran trees within this iconic habitat. In the New Forest general conservation policy is to remove the non-native pines from the high quality old growth woodland in which Calicium parvum occurs, and it has survived mainly due to the retention of highly aesthetic veteran pines dating back to the 19th century during pine felling operations.
Britain: Near Threatened
Scotland: Priority Taxon for Biodiversity in Scotland
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)