Flora of New Zealand Series

Type : Stereocaulon paschale (L.) Hoffm. [=Lichen paschalis L.]

Description : Flora (1985: 542–543).

Stereocaulon, included in the monospecific family Stereocaulaceae (Stenroos et al. 2002c; Eriksson et al. 2004; Pennycook & Galloway 2004; Eriksson 2005; Myllys et al. 2005), comprises c. 130 species worldwide (Dodge 1929; Lamb 1951, 1977, 1978; Kershaw 1960; Sérusiaux 1979a; Mineta 1984; Lewis Smith & Øvstedal 1991; Sipman 1998; Øvstedal & Lewis Smith 2001; Ryan 2002e; Högnabba 2006). Although most species have a dimorphic thallus comprising a primary crustose thallus from which a secondary thallus of often richly branched stalks (pseudopodetia) arises, supporting the phyllocladia and apothecia, several crustose taxa have been recognised in recent years (Purvis & James 1985; Fryday & Coppins 1996b; Fryday & Glew 2003; Högnabba 2006). The accounts of the late Mackenzie Lamb (Lamb 1951, 1977, 1978) are the systematic basis for the genus worldwide, but are only a synopsis of the large world monograph that he had long hoped to produce from the very considerable materials that he accumulated during the years that he was Director of the Farlow Herbarium at Harvard University. Species of Stereocaulon, because of their ability actively to fix nitrogen through the cyanobacteria in their cephalodia, have a distinctive ecological importance in disturbed habitats, where they are often dominant components of successional vegetation. Their presumed contribution to nitrogen budgets of grasslands, riverine gravels, volcanic soils and other nitrogen-limited ecosystems is still very poorly known in detail and is a field ripe for investigation.

Recent molecular and developmental studies on cladoniiform lichens cast doubt on the integrity of the families Cladoniaceae and Stereocaulaceae as independent entities and on the definition of podetium and pseudopodetium (Jahns et al. 1995b; Stenroos & DePriest 1998a; Döring et al. 1999; Hammer 2000; Wedin et al. 2000a; Stenroos et al. 2002c). However, a recent molecular study (Myllys et al. 2005) based on analysis of beta-tubulin, GAPDH and SSU rDNA sequences shows the family Stereocaulaceae to comprise Stereocaulon (with Muhria nested in Stereocaulon) and Lepraria (with Leproloma nested within it). This confirms results from the ITS study of Ekman & Tønsberg (2002) and supports an emendation of Stereocaulaceae to include Lepraria, Muhria and Stereocaulon. A very recent molecular phylogenetic study of 49 taxa in Stereocaulon confirms that crustose, as well as erect, shrubby species belong in this genus, with the crustose, monospecific genus Muhria securely nested within Stereocaulon (Högnabba 2006). In this study, Stereocaulon is confirmed as a monophyletic group, but the published phylogeny (Högnabba 2006) does not reflect the current infrageneric classification (Lamb 1977). Twelve species are recorded here.