Anamorph: Fruit-bodies to 700 µm in height and 80 µm diam., cylindrical and pointed, sometimes branched like antlers, pale yellow and sometimes appearing slightly felty, erumpent, composed of an inner core of interwoven hyphae 1.5-2 µm diam. within a gelatinous matrix and an outer layer of vertically arranged hyphae with swollen tips. Conidiophores not clearly distinguished. Conidiogenous cells 18-28 x 3-4 µm at the base, ± cylindrical but irregular and usually slightly tapering, fairly thick-walled, apiculate, ocasionally branched, proliferating sympodially with very prominent denticles. Conidia 7-9.5 x 3-3.5 µm, cylindrical to clavate, the apex rounded and the base acute and often attenuated, usually developing a ± median septum, thin-walled, hyaline, smooth, without a gelatinous sheath or appendages.
Teleomorph: Stromata absent. Ascomata apothecia, 600-1000 µm diam. and 200-250 µm thick, discoid, short-stalked, erumpent, pale yellow, mintely downy or with scattered short hairs, the cup with an outer layer of thick-walled interwoven hyphal cells and a gelatinous medulla similar to that of the anamorph. Hymenium 45-55 µm in height. Interascal tissue of copious simple paraphyses 1-1.5 µm diam. with globose to pyriform tips 4-5 µm diam. Asci 32-35 x 7-8.5 µm, cylindrical to clavate, thin-walled, short-stalked to almost sessile, without croziers, the apex rounded to truncate and slightly thickened but apparently without an apical ring, not blueing in iodine, 8-spored. Ascospores 6.5-9 x 3.5-4.5 µm, cylindrical to clavate, fairly thick-walled, developing a ± median septum, smooth, apparently without a gelatinous sheath or appendages.
The description is based on dried, rehydrated material.
Not formally assessed, but probably would be treated as of Least Concern. There are currently 31 records in FRDBI, almost all recent. The species may have been under-recorded in the past as a depauperate Calocera species, or it may be spreading as a result of environmental change.
This species is unquestionably distant in phylogenetic terms from the core species of Isaria, but there does not appear to be a genus in which it can be placed. There have been suggestions that Calloriopsis (Helotiaceae) may be an appropriate placement, but the necessary combination has not been made and the family, like many others of the Helotiales, has an uncertain circumscription. Additionally, the type of Isaria friesii has not been re-examined in modern times. The name is retained for the present on the grounds of recent usage.
Associated with a wide range of primarily woody substrata. It appears to be particularly prevalent on Hedera helix, but has also been reported from bark of Acer, Buddleja, Griselinia, Rubus, Salix, Sambucus, Symphoricarpos, Syringa and Viburnum. There is a single report from dead stems of Eupatorium cannabinum.
Widespread in southern England: reported from Berkshire, Buckinghamshire, Cambridgeshire, E Cornwall, Dorset, Hertfordshire, N Somerset, S Somerset, Surrey and S Wiltshire.
Either a saprobe or possibly a mycoparasite; the species frequently occurs on substrata colonised by other fungi. In the material studied, it was associated with parasitized and/or effete fruit-bodies of Melomastia mastoidea.