Gymnosporangium clavariiforme

Phylum: Basidiomycota - Class: Pucciniomycetes - Order: Pucciniales - Family: Pucciniaceae

Gymnosporangium clavariiforme

Rust fungi have complex lifecycles, and some of them even switch host part-way through their development. Gymnosporangium calvariiforme is one such example.

If you notice this strange fungus it will almost certainly be at the stage where it is producing orange fruitbodies on Junipers. Later the fungus produces yellow depressions on the leaves of its secondary host - Hawthorn in the case of this particular fungus.

This picture was taken by Penny Turner with whose kind permission it is shown here and in Pat O'Reilly's new book Fascinated by Fungi, published by First Nature in September 2011.

Identification Guide

Description

On its primary host, Juniper, this fungus produces rusty horns with a rubbery texture; each horn is typically 1cm across and up to 3cm long; they are clustered around stem, usually in the form of a ball.

Juniper trees do not seem to be damaged by this rust fungus, but its alternate host, Hawthorn, is more seriously affected, not only by yellow spots on its leaves but also via the haws (fruits of the Hawthorn), which sprout small white tubes that eventually produce spores. The spores released from the fungus on a hawthorn must contact a Juniper, of course, in order to continue the process.

Spore Print

White.

Habitat & Ecological role

On Junipers as primary host and Hawthorn as alternate host.

Season

The orange rusty horns appear on Junipers in springtime.

Occurrence

Fairly common where there are JuniPers.

Similar species

Many other rust fungi produce orange spots on the leaves of particular plants; others produce yellow, red, purple or black spots. The colour of the fruitbody and the host species infected are aids to identification.

Few people study this fascinating branch of mycology, for which a good microscope is essential.

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.

Top of page...


Fascinated by Fungi, 2nd edn, hardback

If you have found this information helpful, we are sure you would also find our book Fascinated by Fungi by Pat O'Reilly very useful. Author-signed hardback copies at a special discount price are available here...

Other nature books from First Nature...