Isthmomyces macrosporus Z. F. Yu, M. Qiao & R. F. Castaneda sp. nov.

Figs 5, 9d

Etymology.

Greek, macrosporus, referring to the large, great conidia.

Description.

Asexual morph hyphomycetous. Colonies on PDA amber to fawn, reverse fawn, attaining 2 cm diam. after 20 days at 25 °C. Mycelium mostly immersed, composed of branched, septate, slender, colourless hyphae. Conidiophores macronematous, mononematous, cylindrical, erect, straight, unbranched, 0-1-septate, smooth, pale brown, 25-35 × 3.0-3.5 µm . Conidiogenous cells polyblastic, cylindrical, denticulate, sympodial extended, integrated, terminal, pale brown or subhyaline. Conidia acrogenous, isthmospore, long fusiform, hyaline, smooth, 36.5-73.0 µm long, strongly constricted at the conspicuous, narrow, tiny central isthmus, sometime not differentiated, composed of two cellular isthmic-segments: i) basal isthmic-segment clavate, truncated at the base, 1-septate, hyaline or subhyaline, smooth, 19.2-31.1 × 4.5-6.7 µm; ii) apical isthmic-segment 0-1-septate, narrow obclavate, sometimes sub-obspathulate, rounded at the tip, unicellular, guttulate, hyaline or subhyaline, smooth, 21.1-42.0 × 3.3-5.4 µm . Sexual state: unknown.

Type.

China, Hainan Province, Limu Mountain National Conservation Area, on submerged leaves, April 2015, J. Peng. Holotype YMF 1.04518, preserved in a metabolically-inactive state (deep freezing) in the Conservation and Utilization of Bio-Resources in Yunnan. Ex-type culture CGMCC 3.18824.

Notes.

Phylogenetically, Isthmomyces macrosporus is close to I. dissimilis and I. lanceatus . However, I. macrosporus is different from all species within this genus by having larger conidia, obviously brown conidiophores and few denticulate conidiogenous cells (Hoog and Hennebert 1983).