Diploschistes Norman
Type : Diploschistes scruposus (Schreb.) Norman [=Lichen scruposus Schreb.]
Description : Thallus crustose, continuous to areolate, grey-white or brownish or fawn, smooth to warted, often ±pruinose; medulla I+ bluish. Photobiont green, Trebouxia. Ascomata apothecia, at first usually ±perithecia-like, becoming urceolate, immersed; disc black, sometimes white- or grey-pruinose. Thalline exciple present, thick and pruinose, to scarcely distinguished from thallus. True exciple united with thalline exciple, dark-brown to black, of thick-walled, swollen to globose hyphae, immersed in a matrix below, extended into pale brownish periphysoids on upper inside margin, not swollen apically, ±septate, often appearing as fringe in surface view, and presumed to close ascomatal opening under xeric conditions. Epithecium ±colourless to black, sometimes with crystals. Hymenium colourless, I−. Hypothecium colourless to dark-brown or blackish. Hamathecium of flexuous, ±unbranched paraphyses, remotely septate, the apices not swollen, sometimes brownish. Asci elongate–clavate to subcylindrical, the wall ±evenly thickened when mature, the walls I−, not fissitunicate, (1–)4–8-spored. Ascospores broadly ellipsoidal, brown to dark-brown or purplish-black, muriform (producing both macrocephalic and microcephalic types), smooth, lacking a distinct perispore or gelatinous sheath, I− or I+ bluish. Conidiomata pycnidia in raised warts, black. Conidiogenous cells simple or branched at base, elongate–ampulliform, conidia arising apically. Conidia bacillar to elongate–ellipsoidal, truncate to apiculate at base, simple, colourless. Chemistry: para depsides (e.g. lecanoric and diploschistesic acids) or nil.
Key
Diploschistes is a small genus in the family Thelotremataceae (Eriksson et al. 2004; Lücking et al. 2004; Pennycook & Galloway 2004; Eriksson 2005) comprising c. 35 species (Kirk et al. 2001) found in rather arid areas growing on either rock or on soil or overgrowing detritus. It is distinguished from other genera in the family by the combination of the following characters (1): presence of Trebouxia rather than Trentepohlia as photobiont, (2): blackish pigmentation of the pseudoparenchymatous excipulum, (3): presence of lateral paraphyses, (4): absence of a columella (Lumbsch 1989; Guderley et al. 1997; Martín et al. 2003). Diploschistes is widely distributed in arid and semiarid regions of the world, occurring mainly on rocks and soil although facultatively corticolous species are also known. Related genera having Trentepohlia as photobiont have their centre of distribution in the wet tropics and are often corticolous (Lumbsch & Tehler 1998).
Regional systematic treatments discussing systematic position, characters, and history of taxonomic exploration are those of Lumbsch (1987, 1988, 1989, 1993, 2002), Lumbsch & Elix (1985, 1989, 2003), Mies & Lumbsch (1990), Lumbsch & Aptroot (1993), Pant & Upreti (1993), Guderley & Lumbsch (1996) and Lumbsch et al. (1997a). A cladistic analysis of Diploschistes was published by Lumbsch & Tehler (1998) using parsimony analysis with morphological, chemical and ecological characters. The scruposus -group (including D. ocellatus) is supported as monophyletic, whereas the actinostomus -group is paraphyletic. The predicted trend from perithecioid to urceolate ascomata within Diploschistes is supported, and the saxicolous habit is plesiomorphic in comparison with the terricolous habit. Chemistry is more difficult to interpret, however, and no clear evolutionary trend is observed within the genus. Taxa with lecanoric acid do not form a monophyletic group (Lumbsch & Tehler 1998). A recent study of 22 species using ITS sequence data (Martín et al. 2003) confirms the monophyly of Diploschistes with D. occellatus basal to all other species (its affinities to other species of Diploschistes is still unclear), and Diploschistes s. str. comprising two clades, the D. scruposus group and the D. actinostomus group forming a derived monophyletic clade. These results suggest that taxa with perithecioid ascomata are derived from taxa with urceolate ascomata, an evolutionary trend that is opposite to the view derived from cladistic analysis of morphological data (Lumbsch & Tehler 1998). Nine species (comprising 10 taxa) of Diploschistes are recognised in New Zealand (Galloway & Lumbsch 1998).
