Meripilus giganteus

Description

Meripilus giganteus is a large mushroom that grows on tree stumps and the base of certain types of broadleaf trees, especially beech trees. Its caps can be as wide as half a meter.

This mushroom is found in most parts of mainland Europe. In North America, a similar fungus called Meripilus sumstinei is found.

Identifying this species can be tricky because it varies in color and edge thickness as it grows. When young, the edges are blunt and rounded, but they become thinner and sharper as the mushroom matures. When it grows on buried tree roots, it can take on a beautiful, symmetrical rosette shape. If you touch the undersurface of this mushroom, it quickly turns dark brown or black. Because of this staining reaction, some people call it the Black-staining Polypore.

In the past, people thought this large mushroom wasn't edible because its flesh is tough and slightly sour. However, more recent sources say it can be eaten. Younger specimens might taste better, and there are mentions of it being eaten in Japan. It's important to cook it before eating, but for a small number of people, it might still cause stomach discomfort.

Common names: Giant Polypore, Black-Staining Polypore, Japan (トンビマイタケ), German (Riesenporling).

Mushroom Identification

1. Fruiting Bodies

   Fruiting bodies have a diameter ranging from 15.47 to 30.94 inches (50 to 100 cm). They are rounded and bush-like branched, with a tuberous base from which numerous pedunculate branches often depart, ending in flattened caps.

2. Caps

   The caps can reach up to 30 cm in diameter. They are rounded and shingle-like, with a thin-fleshy-leathery texture. The surface of the caps is felty or finely scaly, in shades of chestnut-brown to brown-brown. The edges are wavy and often jagged.

3. Undersurface

   The hymenophore, or the undersurface, is tubular. Initially white, it later turns dirty gray and may become gray or black where in contact. The tubes, measuring 4-6 mm in length, descend along the stem. The pores are small, with a diameter of 0.25–0.5 mm. They are rounded and start solid white, later developing an incised, dirty-gray edge. The density is 3–4 pores per 1 mm.

4. Flesh

   The flesh is initially leathery-meaty or hard-meaty. It later becomes leathery and is either white or pinkish. When cut, it turns black and has a sour taste. When dried, it emits a mushroom smell.

5. Spores

   Spores measure 5-6.5 * 4.5-5.5 μm and are broadly oval or almost round. Sometimes, they are flattened on one side and may have a single drop. The spores are colorless.

6. Spore Print

   White.

7. Habitat

   This species typically thrives in deciduous, coniferous, and mixed forests, primarily among oaks, pines, and spruces. It is commonly found at the base of trunks and stumps, although this is a rare occurrence. Known for causing white rot in wood, it can be observed from late June to late September.

Look-Alikes

1. Grifola frondosa

   While sharing a general resemblance, it can be set apart by its somewhat grayer cap and larger pores.

2. Laetiporus sulphureus

   Exhibits a yellow-orange coloration, and its pores do not become black upon being bruised.

3. Meripilus sumstinei

   Referred to as a "Berkeley's polypore," it is frequently mistaken for M. giganteus in the eastern regions of North America. However, it stands out due to its absence of black-bruising and notably bigger pores.

Treatment

Applying certain soil treatments during planting can offer protection to the roots and enhance their ability to fend off infections. Maintaining optimal growth conditions through methods like aeration, mulching, and irrigation will also contribute to increased resistance against the fungi.

Regularly inspecting and surveying trees under your care should encompass an evaluation of crown development. If issues like crown thinning or dieback are detected, prompt investigation into their causes is essential. While these symptoms might arise from factors like drought or waterlogging, they could also indicate more severe concerns such as Meripilus infection.

It's important to note that existing infections cannot be effectively controlled. In cases where trees are infected, especially in areas accessible to the public, felling them for safety reasons is typically the most viable course of action.

History

Christiaan Hendrik Persoon first termed this polypore fungus Boletus giganteus. Later, Finnish mycologist Petter Adolf Karsten renamed it Meripilus giganteus in 1882. In the Meripilus genus, it's the primary species in Britain.

A similar fungus, Meripilus sumstinei (also called Blackening Polypore), exists in North America. Initially a weak parasite, it turns saprobic after its host tree dies. It forms rosettes and brackets that persist on dead stumps for years.

The name "Meripilus" comes from "meri-" (part) and "pil" or "pile" (cap), hinting at multi-part caps in this genus. "Giganteus" aptly portrays these fungi's enormous size.

Synonyms and Varieties

• Agaricus multiplex Dill., 1719

• Boletus acanthoides Bull., 1791

• Boletus cornutus J.F. Gmelin (1792), Systema naturae, Edn 13, 2, p. 1437

• Boletus elegans Bolton, 1788

• Boletus giganteus Persoon (1794), in Römer, Neues magazin für die botanik, 1, p. 108 (Basionyme) Sanctionnement : Fries (1821)

• Boletus imbricatus Sowerby (1797), Coloured figures of English fungi or mushrooms, tab. 86

• Caloporus acanthoides (Bulliard) Quélet (1888), Flore mycologique de la France et des pays limitrophes, p. 406

• Cladomeris acanthoides (Bulliard) Quélet (1886), Enchiridion fungorum in Europa media et praesertim in Gallia vigentium, p. 168

• Cladomeris gigantea (Persoon) Quélet (1886), Enchiridion fungorum in Europa media et praesertim in Gallia vigentium, p. 168

• Cladomeris gigantea var. fumosa Gillot & Lucand (1890), Société d'histoire naturelle d'Autun, Bulletin, 3, p. 155

• Cladomeris giganteus (Pers.) Quél., 1886

• Clavaria aequivoca Holmskjold (1790), Beata ruris otia fungis danicis, 1, tab. 13

• Flabellopilus giganteus (Persoon) Kotlaba & Pouzar (1957), Ceská mykologie, 11(3), p. 155

• Grifola acanthoides (Bulliard) Pilát (1934), Beihefte zum botanischen centralblatt, zweite abteilung, 52, p. 53

• Grifola gigantea (Persoon) Pilát (1934), Beihefte zum botanischen centralblatt, zweite abteilung, 52, p. 35

• Grifola lentifrondosa Murrill, 1904

• Grifola sumstinei Murrill, 1904

• Meripilus lentifrondosa (Murrill) M.J. Larsen & Lombard, 1988

• Merisma acanthoides (Bulliard) Gillet (1877), Les hyménomycètes, ou description de tous les champignons (fungi) qui croissent en France, p. 689

• Merisma giganteus (Persoon) Gillet (1877), Les hyménomycètes, ou description de tous les champignons (fungi) qui croissent en France, p. 689

• Polypilus giganteus (Persoon) Donk (1933), Mededeelingen van de Nederlandsche mycologische vereeniging, 22, p. 122

• Polyporus acanthoides (Bulliard) Fries (1838) [1836-38], Epicrisis systematis mycologici, p. 448

• Polyporus giganteus (Persoon) Fries (1821), Systema mycologicum, 1, p. 356

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