Flora of New Zealand Series

Type : Austropeltum glareosum Henssen, Döring & Kantvilas

Description : Thallus squamulose to peltate-foliose, heteromerous, 350–760 μm thick. Upper cortex 280–480(–560) μm thick, of reticulate hyphae 2–4 μm diam., with strongly gelatinised walls. Photobiont green, a species of Chlorococcales, cells ±spherical, 4.5–7(–9) μm diam., penetrated by 1–4 globose haustoria. Medulla 120–245 μm thick of interwoven, thick-walled hyphae 6–10 μm diam. Lower cortex lacking, anchored to substratum by medullary hyphae. Ascomata apothecia, apothecia lecideine, marginal, stalked; the stalk a pseudopodetium, delimited by a boundary tissue. Asci cylindrical, 44–52 × 4.5–10 μm, with an amyloid (I+ blue) tube-structure, 8-spored. Ascospores simple, colourless. Conidiomata pycnidia, marginal. Conidiophores branched. Conidia filiform.

Austropeltum is a monospecific genus, placed initially in the family Stereocaulaceae (Henssen et al. 1992; Eriksson & Hawksworth 1998), but now considered to belong in the family Sphaerophoraceae as evidenced by SSU rDNA sequences (Wedin & Döring 1999; Wedin et al. 2000b; Eriksson et al. 2004; Pennycook & Galloway 2004; Eriksson 2005). It differs from other genera in these families in having a squamulose habit. The genus is characterised by a heteromerous thallus with a thick, heavily gelatinised upper cortex, and stalked, lecideine, glomerulate apothecia. The apothecial stalk is a pseudopodetium, which is delimited from the subhymenium by a pigmented boundary tissue. Asci are 8-spored and have an amyloid tube-structure; the simple ascospores are fusiform and colourless. Filiform conidia are produced laterally and terminally in marginal pycnidia. The sole species, A. glareosum, grows over gritty soil on exposed mountain summits and plateaux in New Zealand and Tasmania.

Molecular studies on Austropeltum (Wedin & Döring 1999) show that lichens with true podetia in the sense of Jahns (1970), such as Neophyllis melacarpa, may belong to the same monophyletic group as lichens having pseudopodetia (such as Austropeltum) and lichens that have no apparent differentiation or formation of such structures (Sphaerophoraceae). These authors also show that the presence of a distinct pigmented tissue of thin-walled, plasma-rich hyphae, forming a boundary between generative and vegetative tissue ("boundary tissue"), may be present in more than one monophyletic group of lichens as currently understood.