Flora of New Zealand Series

Type : Psoroma hypnorum (Vahl) Gray [=Lichen hypnorum Vahl]

Description : Thallus squamulose to small-fruticose or caespitose, orbicular to irregularly spreading, loosely to closely attached, with or without a conspicuous, black, often byssoid prothallus, visible at or beyond margins of thallus and between squamules. Squamules dispersed to imbricate or crowded. Margins entire to variously incised. Medulla white. Primary photobiont green, Myrmecia. Secondary photobiont Nostoc, in prominent to scarcely apparent external cephalodia, present on upper or lower surfaces. Ascomata apothecia, sessile, constricted at base, to 5 (–10) mm diam., disc concave to plane or subconvex, brown to red-brown; thalline margin persistent, raised, squamulose, entire or hirsute, concolorous with thallus. Hymenium I+ dark-blue. Hamathecium of paraphyses, simple or branched near apices, apices not swollen or thickened. Asci 8-spored, narrowly clavate or cylindrical; ascus apex K/I+ dark-blue, with a well-defined ring or tube structure. Ascospores simple, colourless, ellipsoidal, often with a warted epispore that is ±apiculate. Conidiomata pycnidia, immersed, pale-brown. Conidia simple, colourless, bacillar. Without any demonstrable secondary chemistry, with the exception of P. buchananii and P. fruticulosum, which are always brownish through deposition of melanins in the upper cortex.

Psoroma is a genus of c. 40 species (Jørgensen 2003c, 2004e) included in the family Pannariaceae (Ekman & Jørgensen 2002; Eriksson et al. 2004; Pennycook & Galloway 2004; Eriksson 2005). It is found most commonly in cool temperate habitats of both Northern and Southern hemispheres (Jørgensen 1978, 1998a, 2000d, 2001b, 2002d; 2003a, 2003c; Holien & Jørgensen 2000; Timdal & Tønsberg 2006), with New Zealand, Tasmania and southern South America being major areas of speciation and including the subantarctic island groups in the South Atlantic, Indian and South Pacific Oceans and extending to Antarctica (Galloway 1985a; Jørgensen & Galloway 1992b; Galloway & Quilhot 1999; Jørgensen & Wedin 1999; Kantvilas & Jarman 1999; Øvstedal & Lewis Smith 2001). Species are small-squamulose or caespitose, generally without any secondary chemistry, a dingy blue iodine reaction of the hymenia, and asci with distinct I+ blue ring structures (Jørgensen 2004a: 248). Large, foliose, leafy species formerly included in Psoroma (e.g. Galloway 1985a; Jørgensen & Galloway 1992b) are now recognised as green species of Pannaria (q.v.) (Jørgensen 2001b; Elvebakk & Galloway 2003). Psoroma as currently circumscribed is still heterogeneous with at least three distinctive groupings within it: (1) the Psoroma hypnorum group, or Psoroma s. str., (2) the Psoroma implexum group and (3) the Psoroma asperellum group (Elvebakk, unpubl. obs.). In this account, 16 taxa are recorded, although several undescribed species are known and it is recognised that more work needs to be done on this genus (and its close relatives), both in New Zealand as well as in other temperate Southern Hemisphere regions.