Flora of New Zealand Series

≡*Corticium arachnoideum Berk., Ann. Mag. nat. Hist. 13: 345 (1844).

Description : Basidioma corticioid, effuse, thin and loose, creamy or whitish to buff, seasonal; mycelium with numerous subglobose creamy sclerotial bodies; forming massive circular brown lesions with white funiculose margins on colonies of Desmococcoid green algae, Lecanora conizaeoides, also parasitic on a wide range of other crustose and foliose lichens (e.g. Physcia adscendens), and also on surrounding tree bark. Basidia clavate, 2(–4) spored, 20–30 × 5–7 μm, with 2–4 (mainly 2) sterigmata. Basidiospores narrowly ellipsoidal, thin-walled, 5–9(–12) × 2.5–7 μm.

S: Canterbury (Christchurch), Otago (Leith Valley, Northern Cemetery Dunedin), Southland (Tiwai Point). On introduced deciduous trees (Cydonia, Malus, Pseudoplatanus, Quercus, Tilia), often overgrowing and probably parasitic on free-living algae (it forms conspicuous round colonies on swards of Trentepohlia on shaded concrete power poles) and lichens, in sites of moderate to heavy atmospheric pollution. Also on shaded swards of Trentepohlia on gravestones, where it forms distinctive, interlacing, pale rings of infection, contrasting with the orange-red algal cover. First noted from trees in Riccarton Bush in Christchurch (Galloway 1995c: 206), it was subsequently recorded more widely in Christchurch, and also from central Dunedin and Tiwai Point in Southland (Johnson et al. 1998). It also occurs on fruit trees in orchards in the Teviot Valley (Central Otago). Known also from Great Britain, Europe, Scandinavia, Belarus, North Africa, North America, South America (Diederich 1986, 2003, 2004c; Triebel & Scholz 2001; Hafellner et al. 2002; Yurchenko & Golubkov 2003).

Cosmopolitan

Illustrations : Arvidsson (1976: figs 1A–C; 1979: 287, fig. 1; 289, fig. 2A–D); Hawksworth (1983a: 37, fig. 15); Gilbert (1988: 184, fig. 1); Parmasto (1998: 65, fig. 2).

* Athelia arachnoidea is characterised by: the lichenicolous/algicolous/muscicolous habit; infections developing on crustose (occasionally also foliose) lichens or green algal swards on tree trunks in polluted areas – the infections are distinguished by their marginal, white, radiating arachnoid hyphal strands. In later stages of development, the tissue of the diseased host becomes brownish and decomposed and sclerotia of the infecting fungus form on the surface (Arvidsson 1976, 1979; Christiansen 1980; Hawksworth 1983a; Gilbert 1988; Parmasto 1998).