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 Add this item to the list  821489 Original description
Remarks (public):This species is characterized by a slender basidiocarp, olivaceo-brownish and concentrically cracked pileus and absence of rosettes in the pileus and stipe cortex. The slender basidiocarps and pileipellis with round cells indicate its taxonomic position in L. subg. Russularia (Basso, 1999; Heilmann-Clausen et al., 1998; Hesler & Smith, 1979). Although presence of rosettes is characteristic of species of Russulaceae, there are several species of L. subg. Russularia lacking rosettes, including North American L. subserifluus Longyear, L. thiersii Hesler & A.H. Sm. L. rufulus Peck, Asian L. hirtipes, L. gracilis and L. glabrigracilis (Hesler & Smith, 1979; Wang & Liu, 2002; observation of XHW). In comparison with these species, L. olivaceorimosellus has frequent olivaceous tinge in the pileus, the more distant lamellae and less reticulate spore ornamentation. Lactarius olivaceorimosellus is similar to North American L. areolatus Hesler &A.H. Sm., L. highlandensis Hesler & Smith and L. rimosellus Peck in the slender basidiocarps and typically areolate rimulose pileus, but the latter three have rosettes in the stipe and pileus cortex and lack macrocystidia. All the three American species are vinaceous brown and lack olivaceous tinge, which would be good field characters to separate these areolate-remulose species. Among the six studied specimens of L. olivaceorimosellus, only the holotype (SFS2016080502) has a well-developed hyphoepithelium-epithelium as the pileipellis. Continuous layer of round cells are not easy to observe in the other five specimens. Instead, most parts of the pileipellis are a cutis composed of loose broad hyphae (4-7 mm) and piles of round cells are very scattered. This is probably due to limited growth of suprapellis and the consequent rupturing of the cuticle. The ITS sequence KX444365 retrieved from GenBank, although showing a little variation, fell into the same terminal clade as the other four samples and we name it as L. olivaceorimosellus. The sample of this sequence is a root tip sample from Q. liaotungensis. This species is most likely a Quercus associated species. 
Description type:Original description 
Description:Basidiocarps small-sized, slender. Pileus 15-50 mm diam. first
hemispherical then applanate with a conical papilla at the center; surface dry, strongly hygrophanous, strongly rugose, concentrically cracked, grayish-brown when young, later brown, dark-brown, reddish-brown, often mixed with olivaceous tinge, center darker, much paler when dry, margin shortly striate in age. Context 0.5-1 mm thick at the half radius of the pileus, cream-pinkish or paler than the lamellae, taste unknown. Lamellae 2-5 mm wide, crowded to moderately distant when young, distant in age, short decurrent, cream-colored to pale ochraceous with olivaceous tinge when young (3A3), reddish-brown in age (5A5), discoloring light brown when bruised. Stipe 25-70 x 1.5-5 mm, equal, solid to hollow, very smooth, hygrophanous, brown, reddish-brown, with grayish-olivaceous tinge at the apex when young, strigose with
orange-brownish hairs and hyphae near the base. Latex watery,
Basidiospores (140/7/6) (6.5)7-8 x 6-7(7.5) um [Q = (1.04)
1.08-1.20(1.25), Q = 1.14 ± 0.04] [holotype: (6.5)7-8 x 6-7 um,
Q = (1.07)1.09-1.20(1.23), Q= 1.15 ± 0.04], subglobose to ellipsoid, mostly broadly ellipsoid; ornamentation up to 1.5 um, mostly 1-1.2 um high, composed of irregular ridges variable in length, partly connected, sometimes forming a zebroid pattern, rarely forming closed meshes, with abundant sub-transparent (weakly amyloid) dots between ridges; plage distally amyloid. Basidia 38-45 x 10-11 um, clavate, 4-spored; sterigmata 5-6 um long. Pleuromacrocystidia rare to moderately abundant, more abundant towards lamella edge, 46-55 x 6-10 um, cylindrical, with a tapering and moniliform apex, often with a sparse content at the apex, projecting up to 15 um beyond the basidia layer. Hymenophoral pseudocystidia moderately abundant, 3-4 um broad, subcylindrical, slightly enlarged at apex or not, with an oleiferic content. Lamella edge sterile, composed of basidioles-like marginal cells and cheilomacrocystidia; basidioles-like marginal cells 9-20 x 4-7 um, clavate, rarely subfusiform, hyaline; cheilomacrocystidia scattered to moderately abundant, 20-31 x 6-9 um, in shape similar to pleuromacrocystidia. Pileipellis a broken hyphoepithelium to epithelium, often with round cells separated and scattered, forming a cutis between piles of round cells, rarely of globose cells forming a continuous layer, 35-50 um thick; isodiametric cells 5-25 x 5-15 mm, terminal cells (5)15-40 x 4-6 um; hyphae beneath (between) the round cells 4-7 um broad. Stipitipellis a cutis, of densely interwoven hyphae mostly parallel with the stipe length; hyphae 3-7(10) um broad, yellowish brown, terminal cells 20-55 x 3-6 um, mostly slightly enlarged at apex. Hymenophoral trama irregular, of hyphae 3-10(13) um broad and scattered pale yellowish lactifers 3-12 um broad. Pileus and stipe trama lacking rosettes. Clamp connections absent.
Taxon name: