Meripilus giganteus

What You Should Know

Meripilus giganteus is a common Polypore which can be found growing in large numbers at the base of Beech and Oak trees from Summer to Autumn.

This fungus is parasitic and becomes saprobic once the host has died. It is a short-lived fungus that quickly rots away but can cause soft rot to form before developing into white rot. It primarily affects the main root structure of a tree, breaking down its pectin, causing its wood to become brittle and therefore more likely to fracture.

The giant polypore was previously considered inedible, due to its very coarse flesh and mildly acidic taste, but more recent sources list it as edible. Younger specimens may be more palatable; one author notes that it is "eaten in Japan". Also, it may be mistakenly consumed because of its resemblance with the edible species commonly known as Hen of the Woods (Grifola frondosa).

Other names: Giant Polypore, Black-Staining Polypore.

Meripilus giganteus Mushroom Identification

1. Fruiting body

   50-80cm across. Made up of rosette formations with short stems fusing at a common base. Each of the fan-shaped caps ranges from 10-30cm across / 1-2cm thick. Upper surface concentrically zoned light and darker brown. Covered in fine brown scales; radially grooved. The flesh is white, soft, and fibrous.

2. Pores and spore

   Late in forming; 3-4mm, sub circular shape. White(ish) bruising blackish.

3. Spore Print

   White.

4. Habitat and season

   At the base of deciduous trees or stumps; mainly beech or oak. Can grow from roots of the tree away from trunk appearing independent of a tree.

5. Possible Confusion

   Hen of the Woods, Grifola frondosa, pictured, which is edible but does not bruise black, has more of grey color and is usually more frondose.

Meripilus giganteus Similar Species

The polypore fungus Grifola frondosa is similar in overall appearance but may be distinguished by its more grayish cap, and larger pores. Bondarzewia berkeleyi or "Berkeley's polypore" is often confused with M. giganteus (or M. sumstinei) in eastern North America but can be distinguished by its lack of black-bruising and much larger pores.

Meripilus giganteus Treatment

Some soil treatments, if used at the time of planting, may protect the roots and help resist infection. Maintaining optimum growing conditions by aeration, mulching and irrigation will also help resistance to the fungi.

Regular inspections/surveys of trees in your care should include an assessment of crown growth. If crown thinning or dieback is identified the cause must be investigated immediately. Often these symptoms may be caused by drought or waterlogging but they could indicate more serious problems such as Meripilus.

Existing infections cannot be controlled and felling for safety reasons is usually the only option for infected trees, particularly in public access areas.

Meripilus giganteus Taxonomy and Etymology

Originally described by Christiaan Hendrik Persoon, who named it Boletus ngiganteus, this polypore was given its current scientific name in 1882 by the Finnish mycologist Petter Adolf Karsten (1834-1917).

Synonyms of Meripilus giganteus include Boletus giganteus(Pers., Polyporus giganteus (Pers.) Fr., and Grifola gigantea (Pers.) Pilát.

Meripilus giganteus is the type species of the Meripilus genus, in which it is the only species known to occur in Britain.

A very similar species, Meripilus sumstinei (Murrill) M.J. Larsen & Lombard, occurs in North America and is commonly referred to as the Blackening Polypore or the Black-staining Polypore.

Like its European cousin, Meripilus sumstinei is a weak parasite that becomes saprobic once its host tree dies, and so the relatively short-lived rosettes and brackets can appear on the same dead stump and root system for several years after the tree has died.

Meripilus, the genus name, comes from the prefix meri- meaning a part and pil or pile meaning a cap - hence the implication is that caps of fungi in this genus comprise many parts. The specific epithet giganteus means, of course, gigantic, an adjective wholly appropriate to these imposing fungi.

Sources:

Photo 1 - Author: Susan Marley (Creative Commons Attribution 4.0 International)

Photo 2 - Author: Michel Langeveld (Creative Commons Attribution-Share Alike 4.0 International)

Photo 3 - Author: Michel Langeveld (Creative Commons Attribution-Share Alike 4.0 International)

Photo 4 - Author: Peter Gabler (Public Domain)