Russula afroscrobiculata (Verbeken & Van Rooij) Tondel. & Lagaet, in Cao et al., Fungal Diversity 132: 606 (2025)
Index Fungorum number: IF 851194; Mycobank number: MB 851194; Facesoffungi number: FoF 15301; Figs. 1, 2, 3
Basionym – Lactarius afroscrobiculatus Verbeken & Van Rooij, Nova Hedwigia 77: 226 (2003).
Type – ADK 2280 (holotypus BR, isotypus GENT).
Pileus 64–108 mm diam., planoconcave to concave; cuticle sticky and smooth, not peeling, pale yellow to yellowish brown (4A45–5C87), with brown spots when bruised; margin regular when young, undulate when older, very thin, membranaceous and white in some collections. Flesh 10 mm thick at half radius. Stipe 12–36 × 15–33 mm, short, thick, firm, cylindric to clavate; cuticle pale white and sometimes scrobiculate, if so, then pits yellow-brown to dark-brown, small and not very abundant, concentrated in upper half of the stipe, small and irregularly shaped. Lamellae very brittle, decurrent, very dense (13–16 L + l/cm), often with anastomosing veins at the pileus margin; lamellulae 1 l/L, very short, light yellow or darker (4A45), turning brownish yellow when bruised and aged. Context very firm, thick in pileus, chambered to fistulous in stipe; taste first mild to acrid, sometimes becoming bitter, faint resin-like; smell fruity, in older specimens somewhat fish-like. Reaction with guaiac after 8–10 s negative to very weakly positive on stipe and weakly positive on lamellae surfaces, negative with FeSO4 and KOH. Spore print not observed.
Spores broadly ellipsoid, sometimes subglobose or ellipsoid, (6.4–)7.3–7.9(–8.8) × (5.3–)6.1–6.6(–7.4) µm, Q = (1.06–)1.17–1.21(–1.35); ornamentation amyloid, composed of irregular warts, up to 1 µm high, subconical to subspherical, moderately dense [4–5 in a 3 µm diam. circle], mostly isolated, seldom connected with fine lines or aligned [0.5 in a 3 µm diam. circle], size 0.7 µm; suprahilar spot smooth, slightly amyloid. Basidia 45–53 × 5–14 µm, subclavate, with long (7–12 × 2–3 µm) and sharp sterigmata, thin-walled to slightly thickened, 4-spored, contents seldom with oil-like droplets, not reactive in sulfovanillin. Pleurocystidia abundant (700–1000/mm2), 60–90 × 10–15 µm, subcylindrical, highly variable in shape: from tapering upwards to mucronate to slightly clavate, slightly emergent, with contents needle-like and granular, reactive in sulfovanillin (gray), slightly thick-walled, sometimes extending deep into the subhymenium and trama, then 5–8 µm diam., irregularly cylindric, with refractive contents. Lamella edge sterile, cystidia lacking; marginal cells 12–21 × 2–6 µm, clavate to irregularly cylindric, sometimes branched, thin-walled, hyaline. Pileipellis ortochromatic in Cresyl Blue, sharply delimited from underlying context, strongly gelatinized, 120 µm thick, composed of densely interwoven recumbent or ascending hyphae, 2–5 µm diam. No difference between supra- and subpellis. Oleiferous hyphae present in subpellis and hymenophoral trama. Cystidioid hyphae present in both subpellis and hymenophoral trama; their contents finely crystalline. Hyphal terminations near pileus margin densely arranged, rarely branched, hyaline, slightly thick-walled. Terminal elements (20–)23(–26) × (2–)4.5(–7) µm, subclavate to irregularly cylindric, sometimes clavate, then (4–)9(–14) µm wide. Subterminal elements 3–4 µm wide, regularly cylindric, sometimes slightly tortuous, aseptate. Hyphal terminations near pileus center similar in shape, but less densely arranged and terminal elements shorter: (14.5–)19(–23.5) × (3.5–)4.5(–5.5) µm. Pileocystidia at margin abundant, (58–)92(–125) × (4–)5.5(–7) µm, thin-walled, cylindric to subcapitate, slightly tortuous, with finel crystalline contents, slightly reactive in sulfovanillin (gray). Pileocystidia near pileus center similar in size and shape, but less abundant. Acid-resistant incrustations absent. Clamp connections absent in all parts.
Material examined – BENIN, Borgou Province: Wari Maro, 9°09.485N 2°08.846E, 20 Sept. 1998, leg. A. De Kesel (ADK 2280, holotype BR, isotype GENT); Ibid., 9°10.782N 2°09.860E, 25 Sept. 1998, leg. A. De Kesel ADK 2337, BR); Ibid., 9°10.617N 2°09.932E, 13 Sept 2001, leg. A. De Kesel (ADK 3160, BR); Ibid, Savanna with shrubs and trees like Isoberlinia doka and Uapaca togoensis, 9°08.110N 2°10.215E, 9 Oct. 2001, leg. A. De Kesel (ADK 3189, BR); Ibid., Savanna with trees, open canopy with Isoberlinia doka and Uapaca sp., 9°09.541N 2°9.305E, 23 Sep 2001, leg. A. De Kesel (ADK 3236, BR); Ibid., on sandy soil with Isoberlinia doka, 310 m elevation, 17 Jul 2021, leg. C. Manz, F. Hampe and G. Abohoumbo (CM 21–135); Ibid., on sandy soil with Isoberlinia doka, 310 m elevation, 17 Jul 2021, leg. C. Manz, F. Hampe and G. Abohoumbo (CM 21–136); Borgou Province: Doguè, 9°07.249N 1°54.839E, 10 Oct 2001, leg. A. De Kesel ADK 3216, BR); Borgou Province: Gando, in deciduous woodlands dominated by Isoberlinia tomentosa, Isoberlinia doka, and Uapaca togoensis, 7 Jul 2013, leg. D. Maba (MD 335); Borgou Province: Forêt Classée de N’Dali, on sandy soil with Isoberlinia doka, 375 m elevation, 18 Jul 2021, leg. C. Manz, F. Hampe and G. Abohoumbo (CM 21–137); Collines Province: Okpara Forest Park, in Sudanian woodland with Isoberlinia doka, 11 Sep 2019, leg. A. Verbeken (AV 19–003, GENT); Ibid., on sandy soil with Isoberlinia doka, 374 m elevation, 27 Jun 2021, leg. C. Manz, F. Hampe and A. Boukary (CM 21–028). CAMEROON, Western region: Noun division, Foumban subdivision, Mambouo village, in a gallery forest in the savanna region, with Uapaca guineensis, 879 m elevation, 5.6769°N 10.9369°E, 9 May 2012, leg. E. De Crop (EDC 12–031, GENT). TOGO, Centrale region: Parc National Fazao, 16 Jun 2007, leg. A. De Kesel ( (ADK 4387, BR); Forêt Classée d’Alédjo, 29 May 2008, leg. A. De Kesel (ADK 4577, BR); Ibid., 31 May 2008, leg. A. De Kesel (ADK 4599); lbid., 2008, leg. A. Guelly (C 2268).
GenBank – ADK 2280: PP028827 (ITS); EDC 12–031: PP028823 (ITS), PP028849 (LSU), PP033807 (rpb2); CM 21–137[1]: PP028844 (ITS), PQ249297 (LSU), PP033847 (tef1), PP033826 (rpb2); CM 21–136: PP028843 (ITS), PQ249296 (LSU), PP033846 (tef1), PP033825 (rpb2); CM 21–135: PP028842 (ITS), PQ249298 (LSU), PP033845 (tef1), PP033824 (rpb2); CM 21–028: PP028841 (ITS), PQ249295 (LSU), PP033844 (tef1), PP033823 (rpb2); AV 19–003: PP028838 (ITS), PP028863 (LSU), PP033820 (rpb2); C 2268: PP028828 (ITS), PP028853 (LSU); ADK 4599: PP028839 (ITS), PP028864 (LSU), PP033821 (rpb2); ADK 3189: PP028840 (ITS), PP028865 (LSU), PP033822 (rpb2).
Notes – Russula afroscrobiculata comb. nov. was originally described as Lactarius afroscrobiculatus by Van Rooij et al. (2003). Two synapomorphies of milkcaps (Lactarius & Lactifluus) are the presence of latex and pleuropseudocystidia, aseptate extensions of the lactifers in the hymenium. In Lactarius afroscrobiculatus, no latex was observed. However, in tropical environments, less latex can be produced with respect to temperate areas, which could have been an argument to initially describe the species within Lactarius. The pleuropseudocystidia were stated to be very rare (Van Rooij et al. 2003; Verbeken and Walleyn 2010). In none of the collections examined for this study, true pleuropseudocystidia were observed. However, some hymenial cystidia do contain needle-like and granular, refractive structures similar to the appearance of latex. Although these cystidia are differently shaped compared to the ‘regular’ pleurocystidia, and sometimes extend very deep into the subhymenium, we were unable to reject the presence of a septum. Since the pleurocystidia that penetrate deep into the subhymenium are hard to see clearly and the oleiferous hyphae are obvious and abundant in the trama, it is easy to see how some pleurocystidia could have been interpreted as pseudocystidia. On top of that, the most basal part of the pleurocystidia sometimes seems to extend and bend in the trama (Fig. 1c), like in typical pseudocystidia in milkcaps.
Another characteristic that gives Russula afroscrobiculata its Lactarius-like appearance is the scrobiculate stipe. This would be the first species in Russula that contains scrobicules, but it is also not common for African milkcaps to have this trait. However, spotty depressions, which could easily be identified as scrobicules, are described from R. pallidospora J. Blum ex Romagn., which is sister to this species (Fig. 3). It thus begs the question if these structures are true scrobicules.
The phylogenetic analyses revealed that this species indeed does not belong in the genus Lactarius (Fig. 3), but rather it is a member of Russula subg. Brevipedum Buyck & V. Hofstetter. Although deep nodes show low bootstrap values, Russula afroscrobiculata forms a well-supported clade with its sister species Russula pallidospora. Some morphological characters also support this placement in the genus Russula: the absence of latex, and the spores with an ornamentation consisting of warts. The decurrent gills and dull cap colors are typical characteristics for subg. Brevipedum. As previously mentioned, it shares some characteristics with its sister species, R. pallidospora, such as a ‘scrobiculate’ stipe, spores with low, isolated warts, cream-colored lamellae. The unusual pleuropseudocystidia-like cells are however absent in this species.
Remarkable is the lack of any closely related African species. Two morphologically similar, unsequenced African Russula species are R. pallidorimosa Buyck and R. terrena Buyck, known from DR Congo and Zimbabwe respectively. However, some microscopical differences can be discerned, such as the higher spore ornamentation of R. pallidorimosa. R. terrena in its turn has larger spores, undifferentiated marginal cells and lacks lamellulae. Likewise, R. afrodelica Buyck (DR Congo) and R. ochraceorivulosa Buyck (Burundi) are also morphologically similar, but are delimited from R. afroscrobiculata based on molecular data (Fig. 3). Moreover, these species have different spore sizes and ornamentation.
The species occurs in extensively pastured savanna woodlands dominated by Burkea africana and Isoberlinia doka, as well as in savannas dominated by Isoberlinia tomentosa, Uapaca togoensis and/or Detarium sp. and in gallery forests in the savanna region with Uapaca guineensis. Only known from Benin, Cameroon and Togo.
Figure 1 – Russula afroscrobiculata. a Field habit (EDC 12–031) (photo: Eske De Crop). b Scrobicule-like spots on the stipe of the type specimen (ADK 2280) (photo: André De Kesel). c Pleuropseudocystidia- like cells in sulfovanillin, 40 × 10x, EDF stacking, arrows indicate the basal part of the pleurocystidia bending in the trama (MD 335), scale bar = 10 µm. d Pleurocystidium and spores, SEM.
Figure 2 – Russula afroscrobiculata. a Spores (ADK 2880). b Basidioma (ADK 2880). c Pleurocystidia (ADK 2880). d Hyphal terminations of the hymenium (ADK 2880). e Hyphal terminations of the pileipellis (AV 19–003). f Basidia (ADK 2880). g Pileocystidia (AV 19–003). h Section through pileipellis (ADK 2880). Scale bars = 10 µm. Adapted from Van Rooij et al. (2003).
Figure 3 – Phylogram generated from ML analysis with standard boot strapping (1000 replicates), based on combined ITS, LSU, rpb2 and tef1 sequence data for Russula subg. Brevipedum. The combined dataset contains 54 samples and 5 samples from R. subg. Malodorae as an outgroup, with 3227 characters including gaps. 103 sequences, of which 31 of R. afroscrobiculata, were newly generated in this study and deposited in Genbank. ML bootstrap values = 60 are shown.