Macrolepiota clelandii

Either Macrolepiota or Chlorophyllum. KenT would undoubtedly be aware of Chlorophyllum molybdites, which has dirty white to greenish-tinged gills and which gives a greenish-tinged spore print. From the early 2000s studies of the large lepipotoid fungi, such as this one, led to some species (with pure white gills and white spore print) moving from Macrolepiopta to Chlorophyllum. Macroscopically, each genus is a mix, for in each there are species in which the mushrooms are white overall as well as species in which there are mushrooms with caps that have brown scales.

Yep it was all a lot easier when Chlorophyllum just had a single green spored species. When trying to guess which genus this was I came to Macrolepiota largely based on the paper Chlorophyllum and Macrolepiota (Agaricaceae) in Australia by Vellinga 2003 in Australian Systematic Botany 16, 361–370 and references therein particularly Bouger & Syme 1998 and Grgurinovic 1997. I excluded the known members of Chlorophyllum based on macroscopic characters and habitat characteristics as described below. Chlorophyllum molybdites has large fruit bodies (pileus to 240 mm) with a double ring and gills that develop a dull gray green tinge in mature specimens. I’ve not seen this species in the ACT elsewhere I’ve seen it in well-watered grassy areas or in the wet season in northern Australia. Chlorophyllum nothorachodes has a pileus up to 280 mm with a central star-shaped patch and a stipe 25–40(–60) mm wide, species seemingly only known from Canberra garden soil. Chlorophyllum brunneum occurs in various man-made habitats in Europe and North America. In Australia it is found under imported trees (Cupressus macrocarpa, Pinus radiata) and on compost heaps. Illustrations and descriptions show it to have big squames on the pileus. Chlorophyllum hortense has pale basidiocarps with whitish squames on the pileus and a yellowish umbo. The preceding does not rule out any as yet undescribed Chlorophyllum species, but if I have to guess which described species this was I would suggest Macrolepiota clelandii.

In the early years after Vellinga's paper was published, I did occasionally look at the odd macrolepiotoid fungus or two microscopically, to see how it keyed out. Sometimes, a specimen seemed an aberrant form of a species in that paper, or perhaps mostly similar to one species but with some suggestion of another. So I got in the habit of just thinking "Macrolepiota/Chlorophyllum" whenever I saw one of those. Undoubtedly that is me being over-cautious, so when you say that your fungus is most likely Macrolepiota clelandii, I've no problem if that plausible idenification gets recorded on Canberra Nature Map, even if a part of me is saying "yes, but...".

Kent what a great lot of useful information all in one spot! Thanks to you both for helping to increase our knowledge and understanding of these fungi.