Hypocrea sulphurea group

An individual Hypocrea fruit body is roughly globose and small (say around a quarter of a millimetre in diameter) and is called a perithecium. Inside there is a chamber in which the spore-producing organs (the asci) are held and mature spores escape the perithecium via an apical orifice (the ostiole). The fruit bodies develop in groups, united by other tissue so as to form a sheet-like growth, or stroma, which may extend over several square centimetres. You may see the spores within an ascus described in one of two ways: (1) There are 8 spores per ascus, each spore with one transverse septum and the spores generally breaking at the septum so as to yield 16 part-spores in older asci or (2) there are 16 spores per ascus, but when young they are fused in pairs.

In Hypocrea sulphurea the stroma is variable in colour, from vivid yellow to a more subdued light yellow or greyish yellow. The ostioles show up as darker dots on that yellow sheet.  

H. sulphurea and the like are the subject of this paper: B.E. Overton et al (2006). Taxonomy and phylogenetic relationships of nine species of Hypocrea with anamorphs assignable to Trichoderma section Hypocreanum, Studies in Mycology, 56, 39-65. The authors describe a new species, H. victoriensis, and say (page 45): "The morphological similarities between Australian specimens of H. victoriensis and North American specimens of H. sulphurea are striking, but the part-ascospores of the Australian species are more strongly spinulose than the part-ascospores found in H. sulphurea. In addition, none of the Australian specimens occurred on Exidia spp., which is a common substrate in North America. This suggests that ascospore ornamentation and substratum are informative species characteristics for members of the H. sulphurea subclade". The paper notes the distribution of H. sulphurea as Europe, Japan, North America, which makes it tempting to use Hypocrea victoriensis for any bright yellow Australian Hypocrea (and you will see that done on some Australian websites).  

In the Canberra herbarium there is one specimen, from Victoria, identified by Overton as H. sulphurea and with his additional comment "on Exidia sp." This is undated but must post-date the paper. From a photograph it maybe impossible to say whether a stroma is growing on wood or on a fungus in the genus Exidia. Hence I won't go beyond 'Hypocrea sulphurea group' for a photograph of a vivid yellow Hypocrea stroma that is (at least seemingly) on wood.