Rhizocarpon oxydatum Fryday
Biblioth. Lichenol. 88: 140. 2004.

Description:
Thallus orange-red, thin, < 0.05 mm thick, cracked-areolate; areoles flat, 0.4-0.6 mm across, usually contiguous. Photobiont chlorococcoid, cells globose, 10-15 m diam.
Apothecia black, lecideine, orbicular, 0.4-0.6 mm diam., sessile; disc concave; margin thick, raised and persistent, 0.1 mm wide, often radially cracked. Excipulum thick and carbonized, composed of radiating hypahe 5-7 m wide, dark brown throughout. Hypothecium thick, dark brown, carbonaceous, >50 m, mainly composed of vertically orientated hyphae. Hymenium hyaline, 90-100 m thick, I+ blue; epihymenial zone very pale blue, 15-20 m thick. Paraphyses relatively thick 2.0-2.5 m thick, sparingly branched and anastomosing, lax in water, slightly swollen at the apices to 3.5 m with a brown cap. Asci cylindrical, 70-85 x 17-25 m, Rhizocarpon-type. Ascospores hyaline, becoming brown when over-mature, 1-septate, 18-21(-24) x 9-12 m, halonate.
Conidiomata not observed.

Chemistry: no substances detected by TLC.

Distribution & Ecology: Known only from siliceous rocks on Campbell isalnd and the Auckland Islands.

Notes: The orange-red thallus and black apothecia give this species a superficial resemblance to the cosmopolitan species Tremolecia atrata (Ach.) Hertel, from which it is most readily distinguished, macroscopically, by its sessile apothecia. Microscopically R. oxydatum has a strong resemblance to R. hochstetteri (Krb.) Vain., in having medium-sized, 1-septate ascospores and similar paraphyses. It differs from this species mainly in the colour of its thallus and its carbonized exciple, although this latter may not be a good character for distinguishing species in the Subantarctic (see below under Rimularia maculata).
Associated species include Fuscidea subasbolodes, Lecidea lygomma, Placopsis sp. Stereocaulon sp., and Rimularia maculata (see below).

Search for this species on:
Click on a thumb-nail for a full size image.
Use cursors keys, or move mouse to side of image, for next (or previous) image.


Thallus and apothecia


Apothecia