Trichothallus F. Stevens, Bulletin of the Bernice P. Bishop Museum, Honolulu, Hawaii 19: 85 (1925)
Parasitic on host: Sexual morph: Perithecia subglobose, setose. Asci more or less obovoid, 8-spored. Ascospores broadly obovoid, strongly mucronate at base, rounded at apex, 3-septate, with one or both central cells once longitudinally septate. Asexual morph: Thalli composed of irregularly radiating strap-shaped branches, setose, up to 9 mm across, branches vary considerably in width, being sometimes only two cells or about 13 μm wide but generally wider and seldom up to 500 μm wide. Hyphae comprising the thallus branch infrequently so that they appear almost parallel. The ends of marginal hyphae remain closely adpressed to the neighboring ones so that the margin is always crenate and entire and not fimbriate. Thallus cells pale brown to brown, more or less rectangular. Setae scanty or abundant, 3–16-septate, usually slightly constricted at the septa, slightly rough-walled, rounded apex. Conidiophores 4–11-septate, brown to dark brown below and brown to pale brown above, a single whorl of 4–5(–6) phialides is borne just below· the apex; occasionally a second whorl of phialides is present round the apex of the penultimate cell, and rarely a 1- or two-celled branch arising from one of the upper cells may also bear a terminal whorl. Phialides subglobose to ellipsoidal, subhyaline to pale brown, with a more or less cylindrical, tapering, or cup-shaped collarette, borne obliquely near the apex; collarettes directed upwards and are closely adpressed. Phialospores hyaline, ellipsoidal, produced in a sparse slimy mass round the collarettes. Phragmoconidia scattered, occasionally produced in groups, 9–16-septate, pale brown to dark brown, fusiform, curved, tapering toward a cylindrical base which is subhyaline and just above the basal scar, and also tapering toward the subhyaline apex which is subulate or attenuated, do not detach readily from thallus (adapted from Hughes 1965).
Type species: Trichothallus hawaiiensis F. Stevens
Notes: Trichothallus is characterised by pale brown to brown thallus, 4–11-septate, brown to dark brown plokamidomyces-like conidiophores, subglobose to ellipsoidal, subhyaline to pale brown phialides, 9–16-septate, pale brown to dark brown, fusiform phragmoconidia. The sexual morph is characterised by obovoid, 8-spored perithecia, obovoid 3-septate ascospores. Stevens (1925) accommodated Trichothallus in Trichopeltinaceae but Petrak (1950) excluded the genus from Trichopeltaceae based on the presence of setae and characters of the phragmoconidia. Hughes (1953) reported H. hawaiiensis from a Cuban collection, but this material has not been re-examined. During 1963, Trichothallus was found to be common in North and South of New Zealand and around 150 collections were gathered on over 80 different hosts. No cultural studies have been done on Trichothallus and sequence data is lacking. Trichothallus is distinct in having a hypha characterised by a parallel arrangement and do not diverge at right angles on the margins such as in Trichopeltis reptans (Trichopeltaceae). Rossman et al. (2016) reported that Plokamidomyces and Trichopeltheca are synonyms of Trichothallus. Currently, Trichothallus is treated as a distinct genus in Euantennariaceae but molecular data is needed to confirm this taxonomic placement.