Asterophora parasitica (Bull.) Singer - Silky Piggyback

Phylum: Basidiomycota - Class: Agaricomycetes - Order: Agaricales - Family: Lyophyllaceae

Asterophora parasitica - Silky Piggyback, southern England

The Silky Piggyback Asterophora parasitica, pictured above, is very similar to Asterophora lycoperdoides, the Powdery Piggyback, but its cap is covered in fine radial fibrils; this gives it a silky appearance.

Unlike the Powdery Piggyback the gills of this little white mushroom, on which white chlamydospores develop along with basidiospores, are fully formed. The cap expands until it is broadly concave or almost flat.

Asterophora parasitica - closeup picture of the siljky surface

The Silky Piggyback is seen most often on Russula nigricans, Russula densifolia, Russula fellea and Russula foetens; but there are also a few reports of it being found on the decaying caps of certain kinds of milkcaps (Lactarius species).

Only when you look very closely at the caps of these tiny mushrooms can you see the very fine fibres that give a silky feel to the surface (left); it is this feature which has given rise to the common English name Silky Piggyback.

Asterophora parasitica on a decaying brittlegill

Distribution

Almost certainly widespread and common throughout Britain and Ireland, but less commonly noticed because of its diminutive size and its habit of fruiting in decaying fungi that themselves are unlikely to grab the attention, the Silky Piggyback is found also in many parts of mainland Europe and in North America.

Asterophora parasitica, Portugal

Taxonomic history

This species was first described in 1792 by the French mycologist Jean Baptiste Francois (Pierre) Bulliard, who gave it the scientific name Agaricus parasiticus. (Most gilled fungi were initially placed in a giant Agaricus genus, now redistributed to many other genera.) It was German-born mycologist Rolf Singer who, in 1949, transferred this species to its present genus, establishing the currently-accepted scientific name as Asterophora parasitica.

Synonyms of Asterophora parasitica include Agaricus parasiticus Bull., Agaricus umbratus With., Gymnopus parasiticus (Bull.) Gray, and Nyctalis parasitica (Bull.) Fr.

The Silky Piggyback mushrooms shown above were seen nestling between the decaying gills of an old brittlegill mushroom in southern Portugal.

Etymology

Asterophora comes from the Greek words "a'ster" (meaning star) and "phor-" a form of "phero" (meaning to bear or carry) - hence bearing stars, or starry. The coarsely verrucose to blunty spinose chlamydospores do indeed appear to be bearing stars on their surfaces.

The specific epithet parasitica reflects the fact that this little mushroom feeds on the decaying fruitbodies of other larger fungi, although whether it can truly be considered a parasite is questionable.

Toxicity

These tiny and insubstantial mushrooms are generally reported to be inedible. It is unclear whether they contain any very dangerous toxins, but they should certainly not be collected during fungi forages for food.

Identification guide

Cap of Asterophora parasitica

Cap

0.5 to 2cm across; globose or convex; white; covered in silky radial fibrils; increasingly covered in fine powdery chlamydospores.

Gills and stem of Asterophora parasitica

Gills

Initially white or very pale grey, turning brownish; adnate; thick and distant.

Stem

1 to 3cm long and 2 to 4mm diameter; white, browning with age; surface finely woolly; nearly always curved; no stem ring.

Chlamydospores of Asterophora parasitica

Chlamydospores

Pale brown, subfusiform, smooth,12-17 x 9-10µm; forming on the gills rather than on the cap surface (as they do on the caps of the otherwise quite similar Asterophora lycoperdoides).

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Basidiospores

Broadly ovoid, smooth, 5-6 x 3-4µm.

Spore print

White.

Odour/taste

Not significant.

Habitat & Ecological role

Saprobic, on various types of decaying brittlegill fruitbodies, particularly the large blackening species Russula nigricans and Russula densifolia.

Season

Most plentiful in Britain and Ireland from September to November.

Similar species

Asterophora lycoperdoides has a granular cap and rarely has well-formed gills.

Reference Sources

Fascinated by Fungi, Pat O'Reilly 2016.

Dictionary of the Fungi; Paul M. Kirk, Paul F. Cannon, David W. Minter and J. A. Stalpers; CABI, 2008

Taxonomic history and synonym information on these pages is drawn from many sources but in particular from the British Mycological Society's GB Checklist of Fungi and (for basidiomycetes) on Kew's Checklist of the British & Irish Basidiomycota.

Asterophora parasitica, in southern England

Acknowledgement

This page includes pictures kindly contributed by David Kelly.

Other web authorities on this species

Roger Phillips (UK)

Australian National Herbarium

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