This rare lichen appears to starts life as a fungal parasite of Phlyctis species, including the common Phlyctis argena, but soon becomes an independent lichen. Like some other parasites of common lichens, it is curiously restricted to old growth woodlands and parklands and is rare. Distinguished from other Reichlingia clade lichens by the presence of white UV– pruina on the irregularly stellate apothecia and the large spores; Synarthonia astroidestera has bright UV+ orange pruina and Reichlingia anombrophila has smaller spores.
Thallus to 80 μm thick, effuse, white to pale grey, matt, slightly rimose, often with small paler patches of loose hyphae; photobiont trentepohlioid. Apothecia numerous and often crowded, typically irregularly stellate and to 1.2 mm diam, rarely rounded to polygonal and 0.2–0.3 mm diam., red-brown but mostly thinly white-pruinose; in section 65–95 μm tall; epithecium red-brown, K+ pale green; hymenium 40–50 μm tall, colourless or pale red-brown above; hypothecium 15–35 μm tall, colourless to pale straw-coloured; paraphysoids 1–2 μm diam., but brown-walled and to 2.5 μm diam. in the epithecium, a few with apical caps. Ascospores 16–22 (–24) × 5–7 μm, cylindric-obovoid, 3- or 4-septate, the apical cell enlarged; old ascospores brown and warted. Pycnidia not seen. Thallus C–, K± yellow→red (crystals; reaction patchy), KC–, Pd–, or Pd+ yellow in places, UV– (unidentified substance ‘A’ of Coppins & James (1978); ± norstictic acid, probably from the host).
Distinguished from the similarly stellate pruinose apothecia of Synarthonia astroidestera by the UV– pruina, and from other species with stellate apothecia by their lack of pruina. Like Synarthonia astroidestera the pruina may be rubbed off in older specimens, but pale patches on the thallus are another distinctive field feature. Poor specimens might be confused with species with more rounded apothecia, but distinguished from Pachnolepia pruinata by the C– thallus and apothecia, and ascospores with apical cells enlarged, and from R. anombrophila by the longer ascospores. Most thalli are surrounded by surviving uninfected Phlyctis thallus but this can be difficult to differentiate from that of R. zwackhii.
On flushed mesic bark of mature Beech, Ash, Sycamore, Maple and Oak in ancient woodlands and parklands, usually visibly invading Phlyctis argena and rarely P. agelaea thalli and appears to start life as a lichenicolous fungus (hence the patchy norstictic acid), but does soon form patches of thallus with a trentepohlioid photobiont within the host thallus. Occasionally appears completely overgrow its initial host to become a fully independent lichen.
Rare, widespread but scarce in S. & S.W. England (Cornwall to Sussex), very rare in Scotland (E. Perthshire), S.W. & N.W. Wales and Ireland.
Although initially parasitic on a widespread and common lichen, this lichen is both rare and is only found on veteran trees, in open old woodlands and parklands. Widely recorded across southern England, but usually as small populations and very rare beyond. Generally rare in Europe as well link. In some populations a high proportion the occupied trees are Ash so will be vulnerable to Ash Dieback, other large populations are mainly on Beech or Sycamore, while the lichen also occurs on Oak and Maple. The largest population is on Beech in the New Forest, Hampshire, where it has been recorded from 22 woods and in 29 1km grid squares.
Britain: Near Threatened
Wales: Vulnerable
Scotland: Priority Taxon for Biodiversity in Scotland
Cannon, P., Ertz, D., Frisch, A., Aptroot, A., Chambers, S., Coppins, B. J., Sanderson, N. A., Simkin, J. & Wolseley, P. (2020) Revisions of British and Irish Lichens Volume 1 August 2020 Arthoniales: Arthoniaceae. BLS.
Text by Neil A Sanderson, based on Cannon et al (2020)