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Page number:133 
Remarks (internal):R. obscuriformis differs from all other species discussed in this paper by the spores that are "stramineous in mass" - an observation that confirms at least that Murrill did distinguish between pale and darker spore prints in Russula. It is therefore difficult to understand why Singer synonymizes this species with R. sericella (having a white spore print), which has indeed a completely different pileipellis under the microscope.
The discoloring context should, in our opinion, be interpreted as 'graying' context because of the comparison to "R. obscura Romell" (= R. vinosa Lindblad) and the mention of the distinctly grayish lamellae on drying. This graying context, together with the odorless flesh and the very prominent reticulation of the spores, is a combination of characters that does not suggest a place in Russula sect. Xerampelinae (Singer) Jul. Schäff. However, the recently described R. texensis (Buyck et al. 2008) is a fishy Russula with grayish-brownish discoloring context and a weak fishy smell. It has an overall similar color and also similar features of spores and pileipellis. The two taxa differ nevertheless by the much more pronounced reticulation of the spores in R. obscuriformis and the very scarce, smaller and hardly prominent pileocystidia. The spore print color of R. texensis was noted as 'pale' on the gills (a sufficient spore print was not obtained). A dark cream to pale ochre spore print may therefore still be possible and could perhaps match the 'stramineous' color noted by Murrill for R. obscuriformis. It can therefore not be excluded for the moment that Murrill's species is a good member of sect. Xerampelinae.
The use of the synoptic key by Kibby & Fatto (1990) is quite frustrating in the case of R. obscuriformis since the interpretation of many features (in particular cap color, spore print color, peeling and bruising), does not allow for unambiguous coding and therefore does not lead to any reliable identification.
 
Description type:Non-original description 
Description:Russula obscuriformis Murrill, Lloydia 7(4): 312. 1945. Figs 1-6
Microscopic features - Spores broadly ellipsoid, (7.3-)7.7-8.1-8.4(-8.7) x (6.2-)6.4-6.7-7(-7.4) µm, Q = (1.11-)1.15-1.2-1.25(-1.27); ornamentation rather dense, subreticulate to reticulate, composed of conical to hemispherical, often large, strongly amyloid warts, ca (3-)5-7(-8) warts in a 3 µm diam. circle, measuring 0.5-0.7 µm high, interconnected by fine line connections (2-6 in a circle) or fused in ridges (0-4 fusions in the circle); suprahilar plage amyloid. basidia (32-)37.5-40.5-43.5(-45) x (10-)11-12-13(-13.5) µm, 4-spored, clavate. Subhymenium pseudoparenchymatic. Lamellar trama mainly composed of large spherocytes. Hymenial cystidia widely dispersed, less than 500/mm2 and very difficult to observe except near gill edge, measuring ca. 56-80 x 9-14 µm on sides, clavate to fusiform-pedicellate, mucronateappendiculate, thin-walled, with few and ill-defined, SV-negative contents that are not strongly refringent in KOH. Marginal cells not differentiated. Pileipellis orthochromatic in cresyl blue, without incrustations, not sharply delimited from the underlying spherocytes of the context, vaguely divided in a rather poorly gelatinized subpellis and a more dense suprapellis of intricate to ascendant hyphae, with poorly differentiated pileocystidia. Hyphal endings thin-walled and easily collapsing, near margin with terminal cells measuring (19-)24.5-34.2-44(-55) X (2.5-)3-3.2-4(-4.5) µm, slender, attenuated or cylindrical, with apex often more or less abruptly, irregularly or repeatedly constricted and only 1.5-2.5 µm diam., occasionally clavate; subapical cells shorter and often somewhat larger in diam., often branched. Pileocystidia scarce and indistinct, single-celled, arising from the subpellis, cylindrical to subclavate, ca. 4-5.5(7.5) µm wide, with poorly differentiated, granular contents that do not react to sulphovanillin. Clamp connections absent in all parts.
 
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