The Straw Fibrecap (Inosperma cookei) is a small, conical to umbonate mushroom with a honey-yellow to straw cap, usually 2-5 cm across, with a silky, fibrous surface. A faint white veil is often visible at the centre. The stem is pale with a distinct bulb at the base, and the flesh has a bitter-sweet, honey-like smell.
It grows on light soils in deciduous woodland and sometimes under spruce, forming a mycorrhizal partnership with the trees. It fruits from May to October and is widespread and frequent in the UK.
It can be confused with other pale fibrecaps, including Inosperma erubescens and Inosperma adaequatum, so check the cap colour, the bulb and any reddening carefully. Sources disagree on how toxic I. cookei is, and some members of this genus contain muscarine, which can cause sweating, salivation and stomach upset. Inosperma cookei must not be eaten.
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Distribution
Widespread and frequent
Habitat
In deciduous forests, also under spruce, in light soils
Etymology
Inosperma comes from Greek, combining 'is' or 'inos' (fibre) with 'sperma' (seed), literally 'fibre seed'. The first part fits the fibrous look of the genus, though the name was chosen at genus level rather than for this species alone. The epithet cookei is Latin, a genitive form honouring Mordecai Cubitt Cooke, the British mycologist who studied this group. Bresadola named the species for him in 1892.
Cap
A faint white veil is often visible at the centre of the cap, where it can be seen as a pale covering over the central umbo. It is easiest to spot on young caps and may wear away as they expand and age.
| Colour | |
|---|---|
| Surface | Rimose |
| Width | 2 - 5 cm |
Gills
Close gills that begin ash-grey and take on a yellowish-brown tone as the spores mature. They join the stem with a slight notch or a broad, square attachment.
| Colour | |
|---|---|
| Spacing | close |
Flesh
Thin and pale, white to pale yellow. It smells bitter-sweet, a little like honey, which helps to separate it from other fibrecaps.
| Colour | |
|---|---|
| Odour | Bitter-sweet honey |
Stem
Fibrous and streaked, honey-yellow over a paler, whitish ground, with a clearly swollen bulbous base. The bulb is a useful feature when separating this species from similar fibrecaps.
| Colour | |
|---|---|
| Height | 2.5 - 8 cm |
| Width | 3 - 8 mm |
Spores
The spores are bean-shaped, smooth and 7-9 x 4-5 µm. They give a brown spore print.
| Colour | |
|---|---|
| Size | 7-9 x 4-5 μm |
Microscopic Features
The cheilocystidia, found along the gill edge, are pyriform-clavate, meaning pear-shaped to club-shaped. They are widest towards the tip and narrow towards the base.
Classification
- ↳ Phylum: Basidiomycota
- ↳ Subphylum: Agaricomycotina
- ↳ Class: Agaricomycetes
- ↳ Subclass: Agaricomycetidae
- ↳ Order: Agaricales
- ↳ Family: Inocybaceae
- ↳ Genus: Inosperma
Synonyms
- Inocybe cookei Bres.
- Inocybe cookei var. cookei
- Inocybe cookei var. cookei Bres.
Reference Sources
T. Læssøe, J. H. Peterson (2019) Fungi of Temperate Europe Vol. 1. Princeton University Press.
G. Kibby (2023) Mushrooms and Toadstools of Britain & Europe Vol. 4. Geoffrey Kibby.
J. Stangl (2011) The Genus Inocybe in Bavaria. NuAge Print and Copy.
