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Page number:62 
Remarks (internal):Molecular evidence indicates that Lentinus giganteus is better placed in Pleurotus. This is supported by morphology as (1) the lamella-edge is well defined with a broad, sterile layer of differentiated cheilocystidia, similar to those found in some Pleurotus species; (2) basidiomes are soft in texture with short life span, similar to Pleurotus species; (3) the lamellae are broad and well spaced; and (4) development is metavelangiocarpic. Although Corner (1981) established L. subg. Gigantopanus for L. giganteus, our limited data do not support this division.
We collected 11 Pleurotus giganteus specimens from three sites in northern Thailand and one specimen from the original site in Sri Lanka cited in the protologue. The new Sri Lankan collection, identical to that of Corner's (1981) description and our observation of the holotype, is designated as epitype of P. giganteus. Molecular data groups our collections from Thailand with high bootstrap support in a single clade that clusters with sequences of P. giganteus from China, suggesting strain similarity. The Sri Lankan P. giganteus collection forms a sister group with Thai and Chinese collections with 86% bootstrap support. This suggests that the Chinese and Thai collections might have diverged from the Sri Lankan species due to geographical isolation. There are also micro-morphological differences (Table 2), although more collections are needed to confirm whether these are different taxa. Thus we maintain P. giganteus as a single widely variable species. Both Thai and Sri Lankan collections are more closely related to Pleurotus than to Panus and Lentinus. Pleurotus australis, P. smithii, P. cystidiosus, and P. fuscosquamulosus (all Pleurotus subg. Coremiopleurotus) group with all sequenced P. giganteus collections with 100% bootstrap support.
Pleurotus giganteus is closely related to P. subg. Coremiopleurotus, a group of edible species with high commercial value (Zervakis et al. 2004). The relationship suggests that P. giganteus is likely to be a good edible species, confirmed by its present consumption in Sri Lanka (Pegler 1983; Udugama & Wickramaratna 1991). Pleurotus giganteus is also considered edible in China (Dai et al. 2010).
The most commonly and easily cultivated mushrooms in Thailand and other southeast Asian countries are oyster mushrooms (Pleurotus ostreatus (Jacq.) P. Kumm.), ear mushrooms (Auricularia polytricha (Mont.) Sacc.), and straw mushrooms (Volvariella volvacea (Bull.) Singer). Other mushroom species in Lentinula, Lentinus, Ganoderma, and Macrocybe (Hanko 2001, Karunarathna et al. 2011, Boa 2007) and Agrocybe can also be cultivated successfully but require more attention and knowledge (Boa 2007).
Wild mushrooms are one of the higher valued non-timber forest products in northern Thailand (Sysouphanthong et al. 2010, Karunarathna et al. 2011). They provide locals with seasonal food, medicine, and an alternative income while maintaining forest health (Sysouphanthong et al. 2010). The richness of wild mushrooms is also one bioindicator of ecosystem health (Dai & Yang 2009; Du et al. 2011a,b; Sysouphanthong et al. 2010; Egli 2010). Cultivated, non-mycorrhizal mushrooms (e.g., Lentinula edodes (Berk.) Pegler, Pleurotus sajor-caju (Fr.) Singer, Flammulina velutipes (Curtis) Singer, and species of Agaricus, Auricularia, Pleurotus, Agrocybe, and Volvariella) are available year around in northern Thai markets. However, edible wild mushrooms can be found only in the wet season from June to September (Sysouphanthong et al. 2010, Karunarathna et al. 2011). As Pleurotus species form a heterogeneous commercially valuable group of edibles, it is therefore desirable to try to introduce members of this genus as commercial species. Although there are many studies on cultivated and wild edible mushrooms and their nutritional value in the northern hemisphere (Aletor 1995; Latiff et al. 1996; Manzi et al. 1999, 2001; Dermirbas 2000), there is little information available concerning the taxonomy, biodiversity, and economic potential of Pleurotus species in the tropics. Scientific information on wild mushrooms is essential for the introduction of new species for the table (Karunarathna et al. 2011, Sysouphanthong et al. 2010).
Based on the survey of 30 locals through a questionnaire in Chiang Mai and Chiang Rai provinces, we were unable to obtain a clear idea as to whether or not they regard P. giganteus as an edible mushroom. Pleurotus giganteus is not sold in Thai markets during wet season, and most inhabitants of Chiang Mai and Chiang Rai provinces do not consume this wild edible mushroom. Even though P. giganteus has a very good taste (Udugama & Wickramaratna 1991), it is not yet cultivated in Thailand as a commercial mushroom.
 
Description type:Non-original description 
Description:Pleurotus giganteus (Berk.) Karunarathna & K.D. Hyde, comb. nov. Plates 2-4
MycoBank MB 561087
? Lentinus giganteus Berk., Lond. Journ. Bot. 6: 493[bis], pl.17/18 f.2 (1847)
? Pocillaria gigantea (Berk.) Kuntze, Revis. Gen. Pl. 2: 866 (1891)
? Velolentinus giganteus (Berk.) Overeem, Bull. Jard. Bot. Buitenz, 3 sér., 9: 12 (1927)
? Panus giganteus (Berk.) Corner, Beih. Nova Hedwigia 69: 69 (1981)
Type: Sri Lanka, Central Prov., Hautane Range, on ground, July 1844, by Gardner, No 58 (holotype K; Plate 2A-C); Central Prov., Kandy Distr., Deliwala village, 7°14?43.55?N 80°33?51.40?E, elevation 1050 m, rainforest dominated by Swietenia spp. and Artocarpus heterophyllus, 5 June 2009 (mflu11 0018, epitype designated here [Plate 4A]).
Pileus 60-310 mm in diameter, strongly convex to applanate becoming slightly depressed in the centre, dark brown (7F5), towards the margin light brown camel (6D4), grayish orange (5B4) at the marginal area, at centre fibrillose-scaly, surface initially uniformly dark, fuscous brown, fuliginous or black, then fading with age to pale ochraceous or yellowish brown (E8), with a darker centre although sometimes remaining dark, dry, distrupted into small, indefinite, radial, innate squamules, overlain by scanty, pale grey or blackish, verrucose-floccose, concentrically arrange remnants of the veil; margin strongly involute then straight, thin, slightly sulcate-striate. Lamellae moderately crowded with lamellulae of five lengths, decurrent, slightly interveined and anastomosing over the stipe apex, 2-3 mm broad, white to cream (3A2); edge entire, pale ochraceous or yellowish brown (E8). Stipe up to 50-200 mm long, 7-10 mm broad at the apex, 10-15 mm at the base, fusiform, with radicating base, solid, with surface concolorous with the pileus, paler at the apex, finely tomentose with indefinite zones of paler velar remnants in the early stages; veil thin, floccose, pale to dark brown (6F6), soon reduced to floccose remnants but never forming an annulus on the stipe. Context 5-10 mm thick at the disk, submembranous at the pileal margin, white in pileus and stipe, fleshy-spongy, consisting of a dimitic hyphal system with skeletal hyphae.
Generative hyphae (Plate 3e) 4-6 µm in diameter, inflating with a thick or slightly thickened wall, more or less radially parallel but frequently branching and with large clamp connections. Skeletal hyphae (Plate 3d) 6-8 µm in diameter, hyaline of intercalary or terminal origin, becoming very thick-walled with a narrow lumen, tending to taper apically, occasionally with a limited lateral branch. Basidiospores (Plate 3a) 7-9 x 6-7 µm [n = 40, Lm= 8.30 µm, Wm= 6.36 µm, Q= 1.18-1.46, Qm= 1.33] broadly ellipsoid to ellipsoid, white in mass, smooth, with one large oil drop or multiguttulate, inamyloid, thin-walled. The large spores are not cylindrical but rather broadly ellipsoid, although the largest spores become oblong ellipsoid. Basidia (Plate 3c) 25-40 x 8-10 µm, elongate, clavate, bearing 4 sterigmata. Lamella edge sterile with a broad layer of Cheilocystidia (Plate 3b) 15-30 x 6-10 µm, more or less lecythiform with a ventricose base and a small capitellum (3-4 µm) subtended by a narrow neck, hyaline, thin-walled.
Ecology and distribution- solitary on buried rotten wood in rain forest. Widely distributed in Australia, China, Malay Peninsula, Sabah, Sri Lanka, Vietnam (Pegler 1983), Thailand (this study).
 
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