Flora of New Zealand Series

Thallus crustose, effuse, ecorticate or immersed, corticolous or foliicolous. Photobiont green, species of Phycopeltis, Trentepohlia or the Chlorococcaceae. Ascocarps innate, immarginate, rounded to irregular, with a 'rubbed-down' appearance. Ascospores large 2-8 per ascus, muriform, colourless or brown.

Arthothelium is a cosmopolitan genus of c. 80 species included in the family Arthoniaceae, of which some are non-lichenised fungi living as parasymbionts or saprophytes [Santesson Symb. bot. upsal. 12: 92-94 (1952)]. Although the genus has not been closely studied in New Zealand, 8 species were described in Arthonia, in the last century, from collections of John Buchanan and Charles Knight, being transferred to Arthothelium by Müller Argoviensis [ Bull. Herb. Boissier 2, App. 1: 84-85 (1894)]. In this account 7 species are discussed; A. vermiferum Zahlbr. [ T.N.Z.I. 59: 310 (1928)] a foliicolous species from the leaves of Metrosideros colensoi is referred to Chaetothyrium, a genus of non-lichenised fungi (Santesson loc. cit. p. 93).