Bolbitius titubans - Yellow Fieldcap

Taxonomy

Phylum: Basidiomycota

Class: Agaricomycetes

Order: Agaricales

Common synonym(s)

Bolbitious vitellinus

This little mushroom of rich grassland and roadside verges (and occasionally also on damp woodchip mulch) goes from a yellow 'egg on a stick' via a pinkish parasol stage to a mid-to-dark brown or, in hot dry weather, light ochre mushroom in less than a day. It is also known as the Egg Yolk Fungus.

Rotting hay and old cow pats are the main habitats of this delicate little fungus. It fruits through most of the year, often in full sunlight.

In the picture on the left, taken at midday, the caps of four young fruit bodies are just beginning to expand...

...and in this picture, taken five hours later, the caps have expanded fully, faded from yellow to white, and are now beginning to shrivel. By the following day there was almost no evidence of the fruit bodies left.

Bolbitius titubans - cap with striate margin

Only at the in-between stage are the marginal striations clearly visible. On warm summer days the sticky surface of young caps dries to a silky finish, and then the caps begin greying from the margin. Pale brown spores fall from adnexed and almost free gills that age from straw-yellow through cinnamon to rusty-brown.

Identification Guide

	Cap 1 to 4cm in diameter at maturity, the caps are at first egg-shaped and chrome-yellow, soon expanding like a parasol as they mature and rapidly greying from the margin. The surface is smooth and viscid. The cap flesh is very thin and easily splits from the edge.
	Gills Adnate and pale yellow, the moderately spaced gills become cinnamon coloured as the spores mature.
Stem	2 to 4mm in diameter, white with a yellow tint; slightly granular near the apex and downy as the base. The stem, which has no ring, is hollow and very fragile.
Spore print	Cinnamon to rust brown.
Odour/taste	Not distinctive.
Habitat	On rotting straw and in recently manured grassland; occasionally on woodchip mulch; appearing within two days of rain, but then lasting little more than 24 hours.
Season	June to October.
Occurrence	Very common.