What You Should Know
Gymnosporangium clavariiforme have complex lifecycles, and some of them even switch hosts part-way through their development. The fruiting bodies can be quite spectacular, growing to 3 cm long and rich orange in color. They appear in clusters growing directly from the wood of the branches of Wild Juniper (Juniperus communis). Since it causes an increase in either the number or size of its host’s cells (or both) it is also classed as a gall causer. The second generation of galls appears in summer on Hawthorn.
When flushing, it can appear from a distance as though the tree is on fire and it has been suggested that a Middle Eastern species of Gymnosporangium may have been responsible for the story of the burning bush in the Bible. In dry weather, these structures disappear and all that is visible is a slightly swollen area on the host stem.
The fungus does not cause serious damage to junipers, but hawthorns can suffer a serious loss of haw production due to the effects of the fungus.
Old scientific names include: Podisoma clavariaeforme; Tremella clavariaeforme; Tremella clavariaeformis; Podisoma clavariiforme; Podisoma juniperi-communisю
Other names: Tongues of Fire.
Gymnosporangium clavariiforme Mushroom Identification
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 the 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, to continue the process.
Habitat & Ecological Role
On Junipers as primary host and Hawthorn as an alternate host.
The orange rusty horns appear on Junipers in springtime.
Many other rust fungi produce orange spots on the leaves of particular plants; others produce yellow, red, purple or black spots. The color of the fruitbody and the host species infected are aids to identification.
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