Flora of New Zealand Series

Type : Arthopyrenia contendens (Nyl.) Müll.Arg. [=Polymeridium contendens (Nyl.) R.C. Harris]

Description : Thallus corticolous, crustose, ecorticate, without a distinct medulla, mostly growing within the upper layers of bark, white, cream or greyish. Lichexanthone (UV+) sometimes present. Photobiont green, Trentepohlia, present or absent. Ascomata perithecia, immersed to superficial, simple or compound with two chambers, hemispherical to subglobose to flask-shaped; ostiole apical or lateral; ascomatal wall of melanised hyphae and bark cells. Hamathecium of loosely trabeculate pseudoparaphyses in a gelatinous matrix, sometimes inspersed with oil droplets. Asci fissitunicate, cylindrical, clavate, ellipsoidal or obclavate, with a broad, usually shallow ocular chamber, 8-spored. Ascospores colourless, cylindrical to elongate-cylindrical, rarely clavate or ellipsoidal, transversely septate, 4–13-locular or muriform; wall not thickened, rarely amyloid, smooth, with a gelatinous perispore. Conidiomata pycnidia, minute, hemispherical to subglobose, immersed. Conidia bacillar, 5–10 × 1 μm.

Polymeridium is included in the family Trypetheliaceae (Eriksson et al. 2004; Pennycook & Galloway 2004; Eriksson 2005). It is a genus of 20 species from mainly tropical regions, and comprises both lichenised and non-lichenised taxa (Harris 1986, 1993; Aptroot et al. 1995, 1997; McCarthy 1995g; Aptroot & Ferraro 2000). In his monograph on the genus, Harris (1993) records that it is a reduced, derived member of the Trypetheliaceae, thalli being simple in construction and lacking a cortex; ascomata are reduced to a simple pseudostromatic wall around the hamathecium and lack the large, complex, and often pigmented pseudostromata of Trypethelium, and lack the compound ascomata of Astrothelium. These reductions are thought by Harris (1993: 620) to be adaptations to drier climates and drier forest types of a group that is characterised as drought-tolerant, relatively fast-growing and adapted to high-light conditions. One species is known from New Zealand (Knight 1883; Harris 1993; McCarthy 1995g), though it is still very poorly known and collected here.