A walk though the park today I was pleasantly surprised to find many small yellow and slightly larger pale mushrooms peppered around in the short grass. And as I suspected, these were actually all the same mushroom species, just in different stages of growth.
The Yellow Fieldcap (Bolbitius titubans) is a very widespread and common little mushroom, fruiting during summer to autumn, but I often see them in mid-late spring time too, as in this case. It mainly frequents well manured grassland but is also found on rotting straw, manure, dung and wood chippings.
When very young, its small cap is distinctly rounded, elliptical or sometimes ball-like and is a striking bright yellow colour. It also has a slimy surface texture which sticks to your finger after a gentle prod of the cap! As is grows, the cap opens into a bell shape and eventually spreads to almost flat. During this process, the viscosity fades as well as the chrome yellow colouring until it is nothing more than a pallid straw colour or greyish-white. Some yellow however does remain (for a while) at the very apex of the cap, and the margin becomes noticeably striated and very thin.
The gills on the underside are pale yellow and quite crowded. With age these change colour too, becoming light brown and eventually rusty brown. This is a good identification feature to look out for on older specimens.
The hollow stem, just like the cap, is very fragile and is relatively long when compared to the size of the cap (this can be helpful for locating them amongst the grass to be honest). On closer inspection you’ll see it is covered in fine white powder and more downy at the base.
And as a quick sign off, it’s interesting (albeit a little confusing) to know that although the common ‘Fieldcap’ name is used, the Yellow Fieldcap isn’t actually part of the Agrocybe genus, which are commonly known as Fieldcaps. So make of that what you will!
QUICK ID TABLE: YELLOW FIELDCAP Bolbitius titubans
CAP / FLESH
1-5cm across. ball shaped or elliptical and chrome yellow when young. Pallid yellow to greyish white, bell shaped to almost flat when older. Striate margin. Thin, fragile flesh.
3-10cm x 0.2-0.4cm. Pale yellow or whitish. Hollow. Covered in fine white powder. Downy base.
GILLS / SPORE PRINT
Adnate to free. Crowded. Pale yellow maturing to light brown, then rusty brown.
HABITAT / SEASON
Manured grassland, rotting straw, dung, wood chip. Mid spring through to autumn.