Flora of New Zealand Series

Type : Thelidium amylaceum (Trevis.) A.Massal. [=Thelidium decipiens (Nyl.) Kremp.]

Thelidium, included in the family Verrucariaceae (McCarthy 2001h; Eriksson et al. 2004; Pennycook & Galloway 2004) comprises c. 100 described species (Zschacke 1934; Orange 1991b; McCarthy 2001h; Breuss 2002e; Kirk et al. 2001). Taxa have a crustose thallus, transversely septate, colourless ascospores, darkly pigmented perithecia and lack hymenial algae. Species are found on limestone and other basic rocks, on damp siliceous rocks and on basic soil. No marine species are known. Japanese species are discussed by Harada (1991, 1992c). A key to taxa occurring in NW Europe is given in Orange (1991b) and nine species occurring in Great Britain are discussed by Orange (1992b). Three species are recorded from Australia (McCarthy 2001h). The relatively simple morphology and anatomy of taxa in Thelidium means that few characters are available for the taxonomist, and "within a single species, relatively minor variations in features such as thallus colour and size and degree of prominence of the perithecia can produce plants [sic] of quite different aspect. The distinction between the genera Verrucaria, Thelidium and Polyblastia is based on spore septation, and a more natural arrangement of the species is unlikely to be achieved in the near future. It is likely that some species of Thelidium are closely related to species placed in these other two genera" (Orange 1991b: 105). Five species are known in New Zealand, though the genus is still poorly understood and collected here.