Bolbitius vitellinus, Egg-yolk Fieldcap, from family Bolbitiaceae, is commonly found on fertilised lawns and rich organic material. Pronunciation is Boll-bit-ee-uss vit-elle-line-uss.
Height and thickness of the stalk of Bolbitius vitellinus is also variable, and can range from 30 to 120mm high with a diameter of 3 to 10mm. The stalk is hollow, and both the stalk and the young cap are fragile and will crumble easily if disturbed.
The yellow stalk is distinctively 'powdery' or scaly, and my observations indicate that this scaliness remains as the fungus ages.
Distribution of Bolbitius vitellinus, according to FungiMap of Royal Botanic Gardens Melbourne, includes eastern NSW, eastern and southern Victoria, Tasmania, southeast SA, and SW Western Australia from about Perth to Esperance. The main fruiting period is April to August.
Note that the middle of the three fungi has a slight central depression in the mature cap, and all stages of maturity feature some degree of 'scaliness' on the stem
Gills age from a pretty yellow to a dirty yellow (below). I obtained a rusty-brown or cinnamon-brown spore print.
My sightings of Bolbitius vitellinus, Egg-yolk Fieldcap
[This will be updated with new sightings]
Hunter Region Botanic Gardens - Heatherbrae, on mulched garden - May, Sep.
This image illustrates the variation in size of mature Egg-yolk Fieldcaps with a slender cap 15mm wide with thin stalks up to about 80mm high, while others I saw had larger, thicker caps and were up to 50mm wide with short stumpy stems.