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 Add this item to the list   828503 Original description
Remarks (public):Notes ― Soehner (1924) described a gasteroid fungus found under oaks in the German region of Bavaria, which he called Hydnangium cereum, but did not select a type collection. In a later paper, Soehner (1941) provided new data and reference codes for several collections of this species, indicating that duplicates of a collection labelled ‘Summer 1921’ were sent to several mycologists such as E. Fischer, O. Mattirolo and C.W Dodge. Dodge & Zeller (1937) considered this collection, which they labelled ʻE. Soehner 527ʼ, as the type of H. cereum. After studying several original collections of H. cereum from E. Soehner’s herbarium at Münich, we found that ʻSoehner no. 527ʼ is the only collection consisting of mature basidiomata, so it is here designated as lectotype. Later on, Hawker (1952) described from Wales, UK, a gasteroid fungus of similar characteristics that she called Hydnangium carneum var. xanthosporum. Type collections of H. cereum and H. carneum var. xanthosporum were compared in the present work, and found to be probably conspecific because of their bisporic basidia, cylindrical thick-walled macrocystidia, and conspicuously ornamented globose spores, with H. cereum being the prioritary name. Interestingly, the presence of hymenial macrocystidia was not observed by Soehner (1924, 1941) in H. cereum, neither by Hawker (1952, 1954), Smith (1962), nor by Pegler et al. (1993) in H. carneum var. xanthosporum, despite them being very conspicuous. Morphological traits as well as genetic data from specimens originating from Central and Southern Europe suggest that this taxon is another sequestrate species of Russula, and therefore the combination R. cerea is here proposed. Phylogenetic inferences suggested that R. cerea belongs to section Ingratae, and probably subsect. Foetentinae. Russula cerea is significantly related to other European sequestrate taxa such as R. pila and R. mistiformis, being macroscopically very similar to both species, but differing because of its thinner membranous pileus, bisporic basidia and presence of thick walled, clavate macrocystidia. All samples of R. cerea seemed genetically similar to each-other, except for JMV20000817-1 from Asturias (Spain), which showed significant differences in ITS (15/564 bp = 2.65%, including a 7 bp insertion) and 28S rDNA (4/851 bp = 0.5%). After microscopically studying this specimen, we have been unable to find any distinct features, so it could represent a cryptic species or maybe a hybrid specimen with either R. pila or R. mistiformis. 
Description type:Original description 
Description:Basidiomata 1–3 cm wide, gasteroid, angiocarpic, subglobose, slightly lobate, sessile, sometimes presenting an inconspicuous sterile base and attached to the substrate by a mycelial strand. Pileus dry, smooth, membranous, translucent, displaying hymenophoral locules, basally open and alveolate in old specimens; initially white, then greyish orange (5B6) to pale brown (6D6) when handled or upon exposure to the air, finally reddish brown (8E8). Hymenophore loculate, labyrinthoid, brown (7D7) to reddish brown (8D8); locules minute, 0.4–1.4 × 0.1–0.3 mm (2–3 per mm), elongated, sinuous; external locules always fertile; fresh spore mass in locules reddish brown (9D6); brown (6E7) in exsiccata. Columella absent or rudimentary, but thin sterile veins can be observed in some specimens. Odour fruity, taste mild. Spores (8–)9.5–12.5(–14) μm, Q = 1, variable in size, globose, orthotropic, echinate, orange to reddish in KOH; warts of irregular length, 1–3 μm high, intense yellow, deeply amyloid, dense, robust, conical or cylindrical, obtuse, longitudinally striate, isolated or fused in groups, often interconnected by low ridges; hilar appendix short, inconspicuous. Basidia typically 2-spored, 40–50 × 18–24 μm, pyriform to clavate, filled with minute, hyaline to dark reddish droplets, soon collapsing; sterigmata 8–10(–12) µm long, cylindrical to conical. Basidioles 22–36 × 10–13 µm, clavate. Macrocystidia abundant, (25–)30–50 × (5–)7–12(–16) μm, cylindrical to cylindro-clavate, wall up to 1 µm, with a dark yellow refractive content, rarely exceeding the basidia in length, resembling pseudocystidia because many of them originate at the deep subhymenium or hymenophoral trama. Paraphysoid cells abundant, 20–42 × 10–15 µm, vesiculose, 1-septate. Subhymenium very thick, pseudoparenchymatous, formed by 2–3 layers of prismatic to globose cells 8–20(–25) µm in diam. Hymenophoral trama reduced, 10 µm thick, formed by hyphae 3–6 µm in diam, and some sphaerocytes 10–20 µm in diam, only present in tramal anastomoses. Pileipellis and context 70–125 µm thick; pileipellis thin, 50–100 µm, consisting of (1) a trichodermal suprapellis of subulate to lageniform, capitulate dermatocystidia, measuring 15–30 × 3–5 µm, that soon collapses into a yellowish mass, and (2) a prosenchymatous subpellis 20–30 µm thick, formed by a dense mesh of interwoven, subgelatinized yellowish hyphae, measuring only 2–2.5 µm in diam. Peridial context formed of interwoven hyaline hyphae 2–5 µm in diam, lacking sphaerocytes. Gloeoplera and thromboplera present in the trama and context. Habitat, Distribution & Season ― Solitary to gregarious, hypogeous, in montane conifer (Abies, Picea, Pinus) or broadleaved (Carpinus, Castanea, Corylus, Fagus, Quercus) forests, commonly on siliceous soil. Summer and autumn. Widely distributed in Temperate and Submediterranean regions of Europe, from almost sea level in Northern countries to 1100 m of altitude in Southern countries. 
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