Anamorph. Acremonium-like.
Mycelium not evident or at most thin, white and spreading. Perithecia cespitose in groups of a few, superficial, nonstromatic but difficult to remove from the substrate, pyriform, 230-250 x 185-220 µm, with an acute papilla, smooth, collapsing by lateral pinching or not collapsing when dry; yellow, not changing color in 3% KOH. Cells at surface of perithecial wall forming textura epidermoidea, often obscured by 2-3 µm wide hyphae. Perithecial wall 10-20 µm wide, comprising a single region of small, indistinct cells; perithecial papilla formed of a palisade of hyphal elements that become progressively narrower and more thin walled toward the ostiolar canal and there merging with the periphyses. Asci clavate, 60-85 x 7-9 µm, apex simple; 8-spored, ascospores 1-striate, completely filling each ascus. Ascospores ellipsoidal, (7-)7.8-9.6 (-10) x 4-4.5(-5) µm, equally 2-celled, not constricted at the septum, smooth to finely spinulose, colorless.
Characteristics in Culture. Colonies grown 14 days at 15-18°C diffuse daylight on CMD, PDA, OA 1 mm diam., white, aerial mycelium lacking, colony comprising tightly compacted hyphae and conidiophores. Colonies grown four days at 20°C, 12 hours dark/ 12 hours near ultraviolet + cool white fluorescent light becoming pale yellow on CMD, PDA and OA. Conidiophores arising from 2-3 µm wide hyphae, macronematous, mononematous, straight, smooth, basally uniseptate, monophialidic, 18-28 x 2-2.5 µm at base; tip 1-1.5 µm wide, thickened, not flared. Conidia (29)35.5-53(-67) x 3.5-4 µm, 0-5-septate, cylindrical but with tip elongated, narrowed and often hooked; base truncate and often with a poorly defined, often foot-like protrusion; produced in basipetal succession and held in white slime.

Known Distribution. New Zealand (South Island).

Habitat. On perithecia of Nectria sp.

Nectriopsis sororicolae Samuels similis, sed ascosporis brevioribus et angustrioribus, (7-)7.8-9.6(-10) x 4-4.5(-5) µm, et statu anamorphicus, Acremonium simulanti, differt.
Holotypus. New Zealand (PDD 46339).

Etymology of the Specific Epithet. Refers to parasitism on a species of a sibling genus of the Hypocreales.
Notes. Nectriopsis sibicola and N. sororicola are most easily distinguished through their anamorphs; their teleomorphs are very similar. On the basis of one collection of N. sibicola and two collections of N. sororicola, ascospores of N. sibicola are somewhat shorter and broader than those of N. sororicola.
Like the anamorph of N. sororicola, the anamorph of N. sibicola cannot be unequivocally placed in any anamorph genus. Conidia of N. sibicola are somewhat Fusarium-like, but N. sibicola is not closely related to any of the known teleomorphs of Fusarium (Gerlach & Nirenberg, 1982). Because the closest relatives of N. sibicola are Nectriopsis species with Acremonium anamorphs, I have followed the same reasoning as that applied to N. sororicola, placing the anamorph of N. sibicola in Acremonium.

Holotype. New Zealand. South Island. Buller: 7 km S of Reefton, Tawhai Forest, on Nectria sp. on Coprosma foetidissima Forst., Samuels, Matsushima & Rossman, 22 May 1983 (PDD 46339).