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Page number:69 
Description type:Non-original description 
Description:Panus giganteus (Berk.) comb. nov. Figure 16 Lentinus giganteus Berk., Hook. Lond. J. Bot. 6 (1847) 403; Petch, Ann. R. bot. Gdn Perad. 4 (1910) 406, 6 (1916) 148; Pegler, Fl. 111. Champ. Mr. Centr. fasc. 1 (1972) 16; Kavaka 3 (1975) 15, with synonymy.
?Clitocybe hypocalamus v. Ov., Bull. Jard. bot. Buitenz. ser. 3, 9 (1927-28) 21. Pileus 5-30 cm wide, convex with inrolled margin, the concave to broadly infundibuliform (up to 10 cm deep) with the margin straightened and acute, blackish, fuscous fuliginous to fuscous brownish, sometimes pallid white tinged brown in the centre, paler with age, the surface brokem into small innate squamules, with scattered larger, soft, grey, and more or less concentric flecks of the veil, minutely white fibrillose near the whitish margin, dry, firm; margin incurved at first, often submembranous and slightly sulcato-striate. Stem 5-18 cm long above ground, 6-30 mm wide, central, subcylindric, attenuate into the ground as a tapering root -12 cm long, stout, solid, fleshy, concolorous with the pileus, thinly white villous with scattered flecks of the veil about the middle, apex paler and scurfy squamulose, base white villous. Veil thin, floccose, greyish white, soon ruptured and remaining as flecks on the stem and pileus, often as a circle of large flecks on the limb of the pileus; ring none or slight and narrow. Gills decurrent, not crowded, 44-52 primaries 4-8 mm wide, 3-5 ranks, often dichotomous once or twice near the stem-apex, white, edge acute and subserrate, not cartilaginous or tough, without hyphal pegs. Flesh 3-9 mm thick in the centre of the pileus, thin and submembranous over the limb (0.5 mm thick), fleshy, firm, rather succulent, becoming tougher in the stem and pileus, white. Smell rather strong, mealy or fungussy (as in Clitocybe nebularis).
On the ground, solitary but often in troops, rooting often around stumps, from buried wood, and apparently from dead roots, in the open and in lowland and mountain forest -3000 m alt. Tropical Asia, Australasia, not uncommon.
Spores 6-8 x 4.5-5.2 µm white in the mass, smooth, ellipsoid, with a large oil-drop or multiguttulate, inamyloid. Basidia 30-50 x 8-9 µm ; sterigmata 4, 4-5 µm long; no acerose basidioles. Hymenium not thickening; subhymenium with short inflated cells 5-15 µm wide. Cheilocystidia 25-35 x 6-10 µm typically ventricose with slender process or neck (6-10 µm long, 2.2-5 µm wide at the base, 1-1.5 µm at the apex) and subglobose head 2-3 µm wide, forming a broad sterile edge to the gill. Pleurocystidia similar to the cheilocystidia, occasionally with 2 sterigma-like processes, scattered.
Hyphae dimitic with skeletal cells; generative hyphae 3-16 µm wide, the cells 20-130 µm long, clamped, inflating and building the fruitbody, walls thin or slightly thickened; skeletal cells -1200 x 4-6 µm intercalary or terminal and then 5-8 µm wide at the base and tapering to thin-walled obtuse tips 1.5-2.5 µm wide, rarely branched, becoming very thick-walled with linear lumen in the older parts of the stem.
Gill-trama with radiate construction, the hyphae branching widely, inflating slightly and invaded by skeletal cells to form an interwoven tissue. Surface of stem with the villous layer formed by two kinds of caulocystidia (i) -60 x 5-8 µm cylindric to subclavate, flexuous, thinwalled, obtuse, and (ii) as the cheilocystidia but with intermediate to the first kind; also with fertile basidia among the caulocystidia at the stem-apex. Surface of pileus with 3-5 tan appressed generative hyphae, radiating, the ends often projecting slightly in groups to form the squamules (especially over the centre of the pileus), bearing singly or in tufts cystidia of two kinds like those of the stem. Veil composed of narrow, closely interwoven, short-celled, and thin-walled hyphae 35 µm wide.
Colour caused by the fuscous walls and slight incrustation of the superficial hyphae of pileus and stem, the longer caulocystidia with pale fuscous sap.
This species, which is one of the larger agarics of Malaysia, is peculiar in Panus, as I define it, because of the broadly ellipsoid 1-guttate spores, the capitate cystidia (as in some species of Pleurotus), and the strongly inflating generative hyphae. But the construction of the gilltrama and the hyphal system are those of Panus. The intercalary widening of the gills is proved by the early appearance of the cheilocystidia which terminate marginal excrescence. They arise when the gills are barely 0.5 mm wide and at c. 1-2 mm from the margin of the pileus. The species aligns most closely with P. javanicus but has resemblances with Pl. olivascens (p. 146) and, perhaps, with Pl. olearius.
It is not clear that the African fungus referred to Lentinus giganteus by Pegler is the same as the Asian-Australasian. Apart from the radial splitting of the pileus (not observed in Asian material) and perhaps the absence of a veil (which is easily destroyed), the African fungus had narrower spores (3-4.2 µm wide), much smaller basidia (17-20 x 45 µm), subclavate cheilocystidia, abundant hyphal pegs, narrow and little differentiated subhymenium (-6 µm thick), narrow generative hyphae (1.5-3 µm wide), and the presence of furcate tapering binding processes (without mention of skeletal hyphae or cells). For these reasons Pegler (1975) placed L. giganteus in sect. Lentinus. I examined the type of L. giganteus at Kew and collections named by Petch. The differences are too great to ascribe to mistake, so that there appear to be two radicicolous species of similar outward appearance..
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