Flora of New Zealand Series

Type : Psora decipiens (Hedw.) Hoffm. [=Lichen decipiens Hedw.]

Descriptions : Flora (1985: 463–464). See also Timdal (2002b: 418).

Psora is a widespread genus of c. 30 species of saxicolous or terricolous lichens included in the family Psoraceae (Eriksson 2004; Pennycook & Galloway 2004). Main occurrences of species appear to be in arid or arctic–alpine areas. It was frequently regarded as a subgenus or section of Lecidea, but the work of Schneider (1980) and Timdal (1984b, 1986, 1987, 2002b) established Psora as an independent genus, though to date no monograph of the genus exists. Psora is characterised by the following features: a squamiform thallus; a well-developed upper cortex of "Scheinrinden"- type (Poelt 1958b; Timdal 1984b, fig. 1G) containing dead photobiont cells throughout the cortex; apothecia containing anthraquinones in the hymenium (mainly parietin in the epithecium) and crystals of calcium oxalate in the hypothecium; amyloid hymenial gelatine; strongly adhering paraphyses; clavate asci without an apical KI+ blue cap, with a KI+ blue tholus containing a deeper KI+ blue channel, with or without a poorly developed ocular chamber, and without a KI+ blue layer inside the ascus wall below the tholus (Malcolm & Galloway: 1997: 187); pycnidia immersed in squamules; and rod-shaped conidia. The most closely related genus to Psora appears to be the crustose Protoblastenia (q.v.). A key to Asian species was recently published by Timdal & Zhurbenko (2004).

The squamiform thallus, that is characteristic for species of Psora appears to have developed convergently in many lichen families. It is an especially common growth form in arid regions and appears to have an adpative advantage for lichens growing on dry soil. Three species of Psora are recorded from New Zealand, two of them occurring most commonly on calcareous rocks and soils (limestone and basic schist), but also on disturbed clay soils in dry grassland, and the third on wind-blown soil in rock joints of schist tors in semi-arid grassland in Central Otago. The genus is still very poorly known and little-studied here. Further specimens should be searched for in arid and semi-arid habitats in Central Otago, Canterbury and inland Marlborough, and in the North I.