Onnia tomentosa
Description
Onnia tomentosa is an inedible species of fungus in the family Hymenochaetaceae. It is frequently found in coniferous forests at higher altitudes, often growing in large groups, rather rare at lower altitudes. It is a plant pathogen, and causes tomentosus root rot, primarily in spruce. It was formerly known as Inonotus tomentosum (Fr.) Teng until molecular phylogenetic analysis led to major revisions in the classification of the Hymenochaetaceae.
The caps often develop on a rather thick, short, brownish, tomentose stipe, one or more arising from a common base, or they may grow directly from the base of a tree.
This fungus is most easily confused with terrestrial polypores in the genera Coltricia and Phaeolus.
Common names: Wooly Velvet Polypore.
Mushroom Identification
Cap
The cap is flat when young, the surface is tomentose, yellow-brown to darker brown, often with a pale edge when actively growing, and often zonate. In mature become a slightly depressed center and contoured in a wave pattern towards the rim, which has a rather sharp edge when old. It is covered in felt that is grey when young and rusty brown when old, up to 10 cm (3.9 in) in diameter.
Stem
The stem is short and thick, dark brown to almost black.
Flesh
The flesh is rather thick and has a soft, spongy upper layer and firm, fibrous lower layer.
Pores
The pores are whitish to brownish, angular, and often become lacerated in age.
Look-Alikes
Coltricia perennis is similar but has a weakly circularly zoned, bare cap. The flesh of the cap is stained uniformly.
Onnia tomentosa Lifecycle
Onnia tomentosa lives in the roots and butts of host trees. The fungus grows across root contacts to invade the root tissues of new hosts. Once roots become infected, the fungus eventually spreads to the root collar where it colonizes the heartwood in the butt of the tree. Annual fruiting bodies appear during moist late summers or in the fall after periods of wet weather, producing spores that are capable of infecting wounded roots. Fungal growth decays the roots and kills trees slowly.
Trees usually do not die until they have been infected for 15 to 20 years. They are frequently windthrown before dying, and often contain large amounts of decay in their bases, which may extend 3 to 6 feet above ground level. Once infected trees die, the fungus may continue to live in large stumps, boles, and large roots for at least 20 years.
Most fires have little effect on the survival of O. tomentosa on a site. Only those fires intense enough to destroy entire root systems are detrimental. Fire, however, sometimes may favor site occupancy by less-susceptible species, reducing the expression and expansion of the disease.
Photo sources:
Photo 1 - Author: Holger Krisp (CC BY 3.0)
Photo 2 - Author: Alan Rockefeller (Alan Rockefeller) (CC BY-SA 3.0)
Photo 3 - Author: Ireen Trummer (CC BY-SA 4.0)
