Basidiocarps (Fig. 4) annual to sometimes perennial; half-resupinate (resupinate with a pileate edge) to resupinate; hard when dry; surface of pileus white to ochraceous, sometimes turning black when old (Fig. 4C); pore surface cream coloured with ochraceous tints, bluish or greenish colour sometimes develops in the tubes (Fig. 4E); context and subiculum with coriaceous consistency and whitish colour; pores 6–10 per mm; tube layer darker than context.

Figure 4. 

Fruiting bodies of the Skeletocutis nivea complex. A S. nemoralis, Korhonen 86 B S. nemoralis, Korhonen 89 C S. nivea, epitype D S. nivea, Miettinen 16350 E S. semipileata with a characteristic bluish colour on pore surface, epitype F S. unguina, holotype.

Hyphal structure: context and subiculum seemingly trimitic (Fig. 5C); hyphae are parallel near cap surface, forming a homogenous, coriaceous texture; skeletal hyphae prevailing, unbranched, thick-walled and often solid, refractive; generative hyphae relatively scarce, clamped, sometimes with (unevenly and irregularly) thickened walls and rarely with sandy encrustation, rarely producing generocystidia (encrusted tips of generative hyphae) with thorny encrustation; ‘binding hyphae’ (Fig. 5C–D) 1–2–4 µm wide, arbuscule-like, simple-septate side-branches of generative hyphae, thin-walled to solid and refractive, developing later than skeletal hyphae and sometimes missing in young parts of context/subiculum but becoming dominant in older parts, sometimes filling up the old tube layer.

Figure 5. 

Microscopic structures of Skeletocutis ochroalba (reproduced after Niemelä (1985)). A spores B encrusted tomentum hyphae arising from dense cortical tissue C section through context, showing generative and skeletal hyphae and ramified side-branches resembling binding hyphae D ramified arbuscule-like binding hypha, arising from a generative hypha E dissepiment edge hyphae F cystidioles and basidioles G vertical section through a dissepiment edge, showing trama, hymenium with a hyphal peg and sparsely encrusted dissepiment edge hyphae.

Trama (Fig. 5G) monomitic to dimitic; hyphae interwoven, tightly subparallel; generative hyphae 1–3 µm wide, usually prevailing, clamped, thin-walled or sometimes with slightly thickened walls; skeletal hyphae (Fig. 6A–C) looking different from those in context and subiculum, sparse, sometimes apparently missing, originating from tramal generative hyphae, winding and irregularly wide (up to 5+ µm) with spacious lumen, walls usually only slightly thickened, slightly refractive; generative hyphae in dissepiment edges (Fig. 5E and G) ca. 2 µm wide, thin-walled, slightly undulating, often somewhat irregularly shaped towards the tips, bare to richly encrusted with sandy crystals.

Figure 6. 

Microscopic structures of the Skeletocutis nivea complex. A S. lepida, tramal skeletal hypha amongst generative hyphae (holotype) B S. semipileata, ends of generative and skeletal hyphae in trama (Miettinen 17135) C S. nemoralis, tube trama and hymenium (holotype) D S. nivea, tube trama and hymenium with encrusted generocystidia (epitype) E S. nivea, basidia (Miettinen 16350) F S. semipileata, basidia (epitype) G S. cummata, the largest basidia in the the S. nivea complex (Niemelä 9088).

Hymenium with fusiform cystidiols (Fig. 5F), often weakly differentiated and inconspicuous but sometimes with strongly elongated apices; hyphal pegs (Fig. 5G) common; heavily encrusted, thorny generocystidia (Fig. 6D) originating from subhymenial hyphae and emerging through hymenium, common especially in older parts of hymenium but sometimes forming amongst dissepiment edge hyphae; basidia (Fig. 6E–G) (5–)6–9(–10) ×(2.2–)2.7–3.7(–4) µm wide, tetrasterigmatic.

Basidiospores (Fig. 7) narrowly allantoid, 2.5–4.0×0.4–0.9 µm, Q’=3.4–7.0, IKI-, CB- (contents CB+).

Figure 7. 

Spores of selected species in the Skeletocutis nivea complex.

The tramal hyphal structure in S. nivea and S. ochroalba has traditionally been described as monomitic. However, our microscopic study revealed two distinct hyphal types existing in the trama of all species in the S. nivea complex. Amongst the normal clamped and thin-walled generative hyphae, there are usually at least some notably wider and slightly thick-walled hyphae which seem to lack clamps. We call these special hyphae tramal skeletal hyphae. They appear to originate from the generative hyphae in the trama and reach down almost to the pore mouths. Usually the lack of clamps, greater width and thicker walls help to tell them apart from generative hyphae in the trama. Although the tramal skeletal hyphae are usually wide and only slightly thick-walled, some specimens of S. nivea had narrower and solid skeletal hyphae in the trama.

Sometimes the tramal hyphal structure is dominated by the skeletal hyphae but sometimes they seem to be missing completely or occur only sporadically in otherwise monomitic tramal structure (at least in S. nemoralis and S. semipileata). They can also be difficult to detect when the whole tramal structure becomes sclerified and generative hyphae also develop thickened walls, which was observed in some specimens of S. nivea. In general, clear detection of tramal skeletal hyphae is easiest in a squash mount from very thin longitudinal slices of the tube layer which have been properly thinned to an almost disintegrated state.

The nature of the arbuscule-like ‘binding hyphae’ has been discussed by David (1982) and Niemelä (1985) and both express some reservations about using the term ‘trimitic’ to describe the S. nivea complex. They point out that the ‘binding hyphae’ in the morphospecies S. nivea and S. ochroalba originate as clampless side-branches of the generative hyphae and, hence, they are not binding hyphae proper, such as those of Trametes. David (1982) studied the staining reactions of the hyphal walls and noted that the walls of the ‘binding hyphae’ are congophilic and non-metachromatic whereas the walls of the skeletal hyphae are non-congophilic and metachromatic. Our observations confirm that all species in the S. nivea complex appear to be similar in this respect.

U.S.A. Florida: Alachua County, Gainesville, indet. angiosperm wood, 20 Nov 2013 Miettinen 17761 (H 7008665, isotype FLAS).

Basidiocarps annual; half-resupinate; up to 1.5 cm wide and 2 mm thick; hard when dry but easy to break apart; pilei thin, protruding up to 5 mm; margin incurved; upper surface minutely rough, matted, white to cream coloured when young, turning ochraceous; context up to 1.5 mm thick, faintly zonate in longitudinal section with thin dark lines separating layers of growth; tube layer up to 0.5 mm thick; pores 8–10(–11) per mm.

Hyphal structure: skeletal hyphae in context / subiculum (1.0–)2.0–2.9(–3.5) µm wide, in trama (1.0–)2.0–4.1(–5.2) µm wide, generative hyphae in trama 1.0–2.0(–2.9) µm wide.

Basidiospores 2.5–3.1(–3.3)×0.5–0.6(–0.7) µm, L=2.86 µm, W=0.55 µm, Q’=(4.0–)4.3–6.0(–6.9), Q=5.18, n=60/2.

The species is known only from two specimens from southern U.S.A., collected from warm temperate deciduous forests where specimens were growing on rather thin twigs of unidentified woody angiosperm.

Calidus (Lat.), warm, refers to the southern distribution.

U.S.A. Arkansas: Marion County, Yellville, indet. angiosperm wood, 25 Oct 2013 Miettinen 17466 (H, FLAS); Florida: (holotype, see above).

Poria coprosmae G. Cunn., Bulletin of the New Zealand Department of Industrial Research 72: 38 (1947).

New Zealand. Westland: Lake Mapourika, Coprosma, Nov 1946 J.M.Dingley (PDD 5252, studied).

Basidiocarps possibly perennial; resupinate to half-resupinate; up to 6 cm wide and 8 mm thick; hard when dry, breaking apart neatly; pilei fleshy, protruding up to 1.7 cm; margin blunt with narrow, sterile ridge on the underside; upper surface minutely rough, matted, white to cream coloured when young, turning ochraceous brown and finally blackish with age; pore surface sometimes with greenish-grey tints deep within the tubes in pileate part; context and subiculum whitish-cream colour to light greyish-brown near contact with substrate (in thick basidiocarps); context up to 5 mm thick, azonate; tube layer from 0.5–1.5 up to 6 mm thick and zonate in perennial basidiocarp, lighter horizontal zones appear where tubes are filled with arbuscule-like ‘binding hyphae’; pores (6–)7–8(–9) per mm.

Hyphal structure: skeletal hyphae in context 2.0–4.3(-5.3) µm wide, in subiculum (1.0–)2.0–3.5(–4.2) µm wide, in trama 2.0–4.0(–5.0) µm wide, generative hyphae in trama 1.0–2.3(–3.0) µm wide.

Basidiospores 2.8–3.2(–3.3)×0.5–0.7 µm, L=2.98 µm, W=0.57 µm, Q’=(4.0–)4.3–6.0(–6.4), Q=5.19, n=60/2.

Available material is very limited but suggests a rather wide, temperate Australasian distribution from Tasmania to southern New Zealand.

AUSTRALIA. Tasmania: Huon Valley, indet. angiosperm wood, 21 Nov 2006 Gates 1898 (H). NEW ZEALAND. Westland: (holotype, see above).

After examining the type, we have chosen to use a previously published name Poria coprosmae as the basionym for this Australasian species. P. coprosmae was described by Cunningham (1947) from Westland, New Zealand. He (Cunningham 1965) later concluded that his P. coprosmae was the same as Polyporus semipileatus Peck but he treated them mistakenly under the name Tyromyces chioneus (Fr.) P. Karst., as explained by Buchanan and Ryvarden (1988).

In their type studies of Polyporaceae species described by Cunningham, Buchanan and Ryvarden (1988) place P. coprosmae in the genus Ceriporiopsis Dom., rejecting placement in Incrustoporia or Skeletocutis based on the absence of encrusted hyphae. Rajchenberg (1995), on the other hand, found the hyphal structure in the holotype and other collections of P. coprosmae in PDD more in line with that of S. nivea. Our studies of the holotype confirm this view with the addition that we also observed encrusted generocystidia and thin-walled skeletal hyphae in the trama, which are characteristic for the S. nivea complex. Macroscopically, the only other studied specimen from Tasmania looks quite different from the type. However, we could not identify any clear microscopic differences and cannot rule out the possibility that the macroscopic differences represent variation between developmental stages. Nevertheless, considering the level of crypticity in the S. nivea complex, we have reservations in stating that our sequenced specimens are truly conspecific with the old type. Thus, we refrain from assigning an epitype for now.

S. nivea occurs in the North Island of New Zealand and it is possible that these two species could overlap as S. nivea has been shown to extend respectively far into the temperate zone in the northern hemisphere. The type specimen is a thin and resupinate basidiocarp on a fallen branch of a Coprosma shrub. The Tasmanian specimen, on the other hand, has evidently been growing on coarse wood and is unique in having a clearly perennial habit with a zonate tube layer.

China. Jilin: Antu, Changbai Mountains, alt. 1300 m, Picea jezoënsis, 18 Sep 1998 Niemelä 6408 & Dai (H 7008666).

Basidiocarps annual; half-resupinate to pileate; up to 3 cm wide and (pilei) up to 1 cm thick; hard when dry but easy to break apart; pilei nodulous or thick but steeply sloping, protruding up to 1 cm; margin of pileus curved downwards, blunt, with narrow, woolly ridge on the underside; upper surface matted to minutely pubescent, white to cream coloured when young, turning ochraceous with almost orange hues; pore surface with ochraceous or sometimes salmon/peach coloured tints, sometimes a greenish-grey tint is visible in the tubes; context and subiculum finally coriaceous but looser and fibrous near cap edge and surface; context faintly zonate in longitudinal section with thin dark lines separating layers of growth; tube layer up to 1 mm thick; pores (5–)7–8(–13) per mm.

Hyphal structure: the outer layer of context typically with a loose, fibrous texture composed of radially orientated encrusted hyphae (tomentum). Skeletal hyphae in context / subiculum (1.0–)2.0–3.5(–5.0) µm wide, in trama 2.0–4.0(–5.0) µm wide, generative hyphae in trama 1.0–2.0(–2.6) µm wide.

Basidiospores (2.8–)2.9–3.4(–3.9)×0.5–0.8(–0.9) µm, L=3.1 µm, W=0.66 µm, Q’=(3.3–)3.8–6.0(–6.6), Q=4.68, n=270/9.

Boreal, Eurasian taiga; known from Fennoscandia, Czech Republic and Far East. The species seems to be rather rare in Europe but possibly more common in the Far East where Spirin (H) has collected it abundantly. The species has been found growing on fallen spruce logs (Picea abies, P. jezoënsis) but also on Abies nephrolepis and Larix sp.

Cummatus (Lat.), resinous, refers to the brown upper surface of basidiomes.

CHINA. Jilin: (holotype, see above). FINLAND. Etelä-Häme: Hämeenlinna, P. abies (fallen, fairly thin, still corticated tree), 17 Sep 2013 Niemelä 9088 & Spirin (H). RUSSIA. Khabarovsk Reg.: Khabarovsk Dist., Levyi Ulun, P. jezoënsis, 21 Aug 2012 Spirin 5472 (H); 5484 (H); Malyi Kukachan, Larix sp., 19 Aug 2012 Spirin 5430 (H); Malyi Niran, P. jezoënsis, 6 Aug 2012 Spirin 4897 (H); Ulun, P. jezoënsis, 26 Aug 2012 Spirin 5676 (H); Solnechny Dist., Igdomi, Abies nephrolepis, VIII.2011 Spirin 3857; Suluk-Makit, P. jezoënsis, 17 Aug 2011 Spirin 4170 (H).

S. cummata is most notably distinguished from other Eurasian species in the S. nivea complex by its occurrence on conifer wood. Spores of S. cummata are also larger than those of angiosperm-dwelling species apart from S. futilis. The pubescence on pileus surface in pileate specimens provides an additional identification cue. Very wide but thin-walled tramal skeletal hyphae seem to be particularly pronounced in this species. All distinctive features of S. cummata are shared with the North American conifer-dwelling species S. ochroalba.

Finland. Uusimaa: Helsinki, Sorbus aucuparia, 24 Sep 2012 Miettinen 15745 (H 7008667).

Basidiocarps annual; half-resupinate; small, up to 5 mm wide and 1.5 mm thick; hard when dry but easy to break apart; pilei very small and nodulous; upper surface white when young, turning yellowish-brown; context and subiculum white; tube layer up to 0.2 mm thick; pores 6–8 per mm.

Hyphal structure: skeletal hyphae in context / subiculum (1.0–)2.0–3.0(–3.3) µm wide, in trama scarce, (1.0–)2.0–3.9(–4.9) µm wide, generative hyphae in trama 1.0–2.0(–3.2) µm wide.

Basidiospores 3.0–4.0×0.7–0.9 µm, L=3.33 µm, W=0.81 µm, Q’=(3.3–)3.4–5.1, Q=4.13, n=30.

The species is known only from the type specimen which was collected from a Betula stand on a disturbed site near the seashore in Helsinki, Finland (hemiboreal zone) where it was growing on rather thin twigs of Sorbus aucuparia.

Futilis (Lat.), fragile, insignificant.

FINLAND: Uusimaa: (holotype, see above).

While macroscopic features may be quite scanty, characteristic trimitic-looking subiculum, skeletal hyphae in trama and encrustations of dissepiment edge hyphae reveal S. futilis to be a member of the S. nivea complex. S. futilis can be distinguished from other species in the complex by thicker spores.

In our analyses, S. futilis constitutes a sister taxon to the rest of the S. nivea complex. The clade also includes S. aff. futilis in North America. Owing to the limited material available, we refrain from judging whether they represent geographic variation within one species or vicariant sister species. The voucher specimens of S. aff. futilis (Lindner DLL2009-067; -068 (CFMR)) are in a rather poor condition, but it seems that the small size of basidiocarps and thick spores are as characteristic for S. aff. futilis as they are for S. futilis.

Uganda. Western Reg.: Kabale Dist., Bwindi Impenetrable National Park, indet. angiosperm wood, 18 Nov 2002 Ipulet F1104 (O 918073, isotype H 7017125).

Basidiocarps annual; half-resupinate; up to 6 mm thick; hard when dry, breaking apart neatly; pilei fleshy, protruding up to 5 mm; margin blunt; upper surface almost smooth, matted, white to cream coloured when young, turning ochraceous brown and finally blackish with age; context and subiculum whitish-cream to light greyish-brown; context up to 5 mm thick, zonate in longitudinal section with thin dark lines separating layers of growth; tube layer from up to 1 mm thick; pores (7–)8–9(–10) per mm.

Hyphal structure: skeletal hyphae in context 2.0–3.2(–4.1) µm wide, in subiculum (1.0–)2.0–3.0(–3.8) µm wide, in trama (1.0–)2.0–3.5(–4.9) µm wide, generative hyphae in trama 1.0–2.0 µm wide.

Basidiospores (2.8–)2.9–3.1×0.5–0.8 µm, L=2.97 µm, W=0.61 µm, Q’=(3.6–)3.8–6.0(–6.2), Q=4.85, n=30.

The species is known only from the type specimen, collected from Bwindi Impenetrable National Park in Uganda where it was reportedly growing on rotting branches.

Impervius (Lat.), impenetrable; the species is morphologically indistinguishable from its kins.

UGANDA. Western Reg.: (holotype, see above).

Uganda. Western Reg.: Kabarole Dist., Kibale National Park, indet. angiosperm wood (leaning dead branch), 28 Oct 2002 Ipulet F761 (H 7017127, isotype O 918074).

Basidiocarps annual; half-resupinate; up to 2.5 cm wide and 6 mm thick; hard when dry, breaking apart neatly; pilei fleshy, protruding up to 5 mm; margin blunt; upper surface almost smooth, matted, white to cream coloured when young, turning ochraceous brown; pore surface cream coloured with greyish tint deep within the tubes; context and subiculum whitish-cream to light greyish-brown; context up to 5 mm thick, faintly zonate in longitudinal section with thin dark lines separating layers of growth; tube layer up to 1.5 mm thick; pores 9–10(–11) per mm.

Hyphal structure: skeletal hyphae in context / subiculum 2.0–3.0(–3.6) µm wide, in trama (1.0–)2.0–4.1(–5.0) µm wide, generative hyphae in trama 1.0–2.0(–2.2) µm wide.

Basidiospores 2.8–3.4×0.5–0.7(–0.8) µm, L=2.96 µm, W=0.6 µm, Q’=(4.0–)4.1–6.0(–6.2), Q=4.97, n=30.

The species is known only from the type specimen, collected from Kibale National Park in Uganda, where it was reportedly growing on a leaning, dead branch.

Named in honour of the pioneering Ugandan mycologist Perpetua Ipulet, who collected the type of this species.

UGANDA. Western Reg.: (holotype, see above).

Japan. Kansai Reg.: Shiga Prefecture, Otsu, indet. angiosperm wood, 7 Nov 2013 Schigel 7684 & Nakamori, Tanaka, Nakano (H 7008661, isotype TFM).

Basidiocarps annual; half-resupinate; pilei up to 3 cm wide, nodulous or up to 4 mm thick and fleshy, blunt edged; upper surface slightly rough, matted, white to cream coloured when young, turning ochraceous; context faintly zonate in longitudinal section with thin dark lines separating layers of growth; tube layer up to 1 mm thick; pores (7–)8–9(–10) per mm.

Hyphal structure: skeletal hyphae in context / subiculum (1.0–)2.0–3.3(–4.0) µm wide, in trama (1.0–)2.0–3.5(–4.9) µm wide, generative hyphae in trama 1.0–2.2(–3.0) µm wide.

Basidiospores See general description of microscopic structures; (2.8–)2.9–3.0(–3.1)×0.5–0.6 µm, L=2.95 µm, W=0.55 µm, Q’=4.8–6.0, Q=5.36, n=90/3.

Available material is limited but suggests a temperate East Asian distribution. Russian specimens represent rather small basidiocarps that were collected from thin, fallen angiosperm branches. The holotype from Japan is a sturdier basidiocarp that was probably growing on a thick branch or a log.

Lepidus (Lat.), charming, nice, elegant.

JAPAN. Kansai Reg.: (holotype, see above). RUSSIA. Khabarovsk Reg.: Khabarovsk Dist., Malyi Niran, Tilia amurensis, 7 Aug 2012 Spirin 4989 (H); Solnechny Dist., Boktor, Quercus mongolica, 8 Aug 2011 Spirin 3964 (H).

Finland. Åland: Lemland, Nåtö, Fraxinus excelsior (fallen branch), 9 Oct 2012 Korhonen 90 (H 7008662).

Basidiocarps annual; resupinate to half-resupinate; bone hard when dry, breaking apart neatly; resupinate basidiocarps up to 10+ cm wide; pilei nodulous to shelf-shaped, often laterally fused and fleshy, protruding up to 1.3 cm; sterile margin often quite pronounced especially in resupinate part; upper surface slightly rough, matted, white to cream coloured when young, turning ochraceous and finally blackish with age; pore surface sometimes with a greenish-grey or turquoise tint emerging within the tubes especially in the pileate part but sometimes in scattered blotches; context sometimes faintly zonate in longitudinal section; tube layer up to 2 mm thick; pores (6–)7–8(–10) per mm.

Hyphal structure: skeletal hyphae in context / subiculum (1.0–)2.0–3.0(–4.0) µm wide, in trama (1.0–)2.0–3.9(–5.0) µm wide, generative hyphae in trama 1.0–2.2(–2.9) µm wide.

Basidiospores (2.8–)2.9–3.2(–4.0)×(0.4–)0.5–0.6(–0.7) µm, L=3.04 µm, W=0.56 µm, Q’=(4.1–)4.8–6.3(–7.8), Q=5.47, n=390/13.

Temperate Eurasia, found in Europe, Iran and Japan; on angiosperm wood, especially Fraxinus, preferring coarse substrates like thick branches or even logs.

Refers to the distribution area of the species in the nemoral zone.

FINLAND. Åland: Jomala, Ramsholm, Fraxinus excelsior (fallen branch), 10 Oct 2012 Korhonen 100 (H); 103 (H); Lemland, Nåtö, F. excelsior (fallen branch) 9 Oct 2012 Korhonen 86 (H); 89 (H); (holotype, see above); Corylus avellana (fallen branch) Korhonen 93 (H). NORWAY. Møre og Romsdal: Sunndal, Populus tremula, 24 Sep 2008 Gaarder 5257 (O 288578); Nord-Trøndelag: Verdal, Sorbus aucuparia, 30 Aug 2006 Klepsland JK06-S080 (O 284195); Sogn og Fjordane: Aurland, Tilia cordata, 10 Jul 2004 Brandrud 149-04 (O 166204). POLAND. Podlaskie Voivodeship: Białowieża National Park, Carpinus betulus (fallen branch), 15 Sep 2012 Korhonen 35 (H); F. excelsior (fallen branch), 15 Sep 2012 Korhonen 28 (H); 31 (H); 18 Sep 2012 Korhonen 83 (H).

S. nemoralis shares its wide distribution in Eurasia with similar-looking S. semipileata. Both species tend to form rather large, half-resupinate basidiocarps with fleshy pilei. S. nemoralis has slightly larger spores and pores than S. semipileata, but the distinction is probably too small for definitive identification.

In Europe, S. nemoralis does not reach as far to the northeast as S. semipileata and appears to be missing in continental Finland. At its north-eastern outpost in Åland Islands, S. nemoralis is rather common, especially in old coppice meadows where it prefers the wood of Fraxinus.

Polyporus niveus Jungh. Praemissa in floram cryptogamicam Javae insulae: 48 (1838).

Indonesia. Central Java: Mount Merapi, Junghuhn 44 (L).

Indonesia. Central Java: Mount Lawu, alt. 2130 m, old-growth montane forest dominated by Castanopsis javanica, indet. angiosperm wood (fallen branch), 22 May 2014 Miettinen 18217 (BO, designated here, duplicate H 7008663). MycoBank No. MBT378098

Basidiocarps annual; half-resupinate; hard when dry, breaking apart neatly; pilei nodulous to shelf-shaped, sometimes laterally fused and quite fleshy, up to 2 cm wide and 5 mm thick, protruding up to 1.3 cm, often connected to wider resupinate part; upper surface almost smooth to slightly rough, matted, white to cream coloured when young, turning ochraceous and finally blackish with age; pore surface often with a greenish-grey or turquoise tint emerging within the tubes particularly in the pileate part but often in scattered blotches; context and subiculum coriaceous, white; context sometimes faintly zonate in longitudinal section; tube layer up to 1 mm thick; pores (7–)8–10(–13) per mm.

Hyphal structure: trama dimitic but sometimes seemingly monomitic with slightly sclerified generative hyphae or sometimes clearly dimitic with solid skeletal hyphae; skeletal hyphae in context / subiculum (1.0–)2.0–3.0(–3.9) µm wide, in trama (1.0–)2.0–3.5(–4.9) µm wide, but only 2–3 µm wide and solid in specimens from New Zealand, generative hyphae in trama 1.0–2.3(–2.8) µm wide.

Basidiospores (2.7–)2.8–3.2(–3.7)×0.5–0.7(–0.8) µm, L=2.96 µm, W=0.56 µm, Q’=(3.9–)4.3–6.0(–6.2), Q=5.27, n=125/5.

From tropical southeast Asia to subtropical New Zealand in the south and temperate China in the north, on angiosperm wood.

CHINA. Jilin: Antu, Changbai Mountains, alt. 1100 m, Alnus sp. (fallen tree crown), 27 Aug 2015 Miettinen 10579.1 (H). INDONESIA. Central Java: (epitype, see above); alt. 2180 m, old-growth montane forest dominated by Castanopsis javanica, indet. angiosperm wood (fallen tree), 22 May 2014 Miettinen 18255 (ANDA, H); (holotype, see above). MALAYSIA. Sabah: Kinabalu Park, alt. 1675 m, lower montane forest, indet. angiosperm wood, 17 Jun 2013 Miettinen 16350 (SNP, H). NEW ZEALAND. Auckland: Hunua Ranges, indet. angiosperm wood, 19 Mar 1996 Ryvarden 38171 (O 916495); 38177 (O 916496).

The holotype of S. nivea is sterile but it possesses the encrusted generocystidia and arbuscule-like ‘binding hyphae’ characteristic to the S. nivea complex. Specimens from New Zealand represent a disjunct population and exhibit aberrant hyphal morphology with clearly dimitic trama. However, they do not stand out phylogenetically (in ITS) from the rest of S. nivea.

Canada. Northern Quebec: Poste-de-la-Baleine, Picea sp., 7 Aug 1982 Niemelä 2695 (H 7017091)

Basidiocarps annual or possibly perennial; half-resupinate to pileate; up to 3 cm wide and (pilei) up to 8 mm thick; hard when dry but easy to break apart; pilei nodulous or thick but steeply sloping, protruding up to 1 cm; margin of pileus curved downwards, blunt, with narrow, woolly, ridge on the underside; upper surface matted to minutely pubescent, white or cream coloured when young, turning ochraceous brown; pore surface cream coloured with ochraceous or sometimes salmon/peach coloured tints, sometimes a greenish-grey tint is visible in the tubes; context and subiculum finally coriaceous but looser and fibrous near cap edge and surface; context faintly zonate in longitudinal section with thin dark lines separating layers of growth; tube layer up to 1 mm thick, sometimes divided by a thin white layer where tubes are filled with arbuscule-like ‘binding hyphae’, otherwise pale buff; pores (6–)7–8(–10) per mm.

Hyphal structure: the outer layer of context typically has a loose, fibrous texture composed of radially orientated hyphae. Skeletal hyphae in context / subiculum (1.0–)2.0–3.5(–4.0) µm wide, in trama 2.0–4.6(–6.2) µm wide, generative hyphae in trama 1.0–2.2(–2.9) µm wide.

Basidiospores (2.8–)2.9–3.7(–4.0)×0.5–0.8 µm, L=3.1 µm, W=0.67 µm, Q’=3.8–6.0(–7.0), Q=4.65, n=70/3.

Boreal North America, possibly quite rare, findings from Northern Quebec and Alberta in Canada; growing on fallen Picea logs.

CANADA. Alberta: William A. Switzer Provincial Park, Picea sp., 24 Jul 2015 Spirin 8854a (H); 8854b (H); Northern Quebec: Poste-de-la-Baleine, Picea sp., 7 Aug 1982 Niemelä 2689.

S. ochroalba is most notably distinguished from other North American species of the S. nivea complex by its occurrence on conifer wood. Surface of the pileus is characteristically pubescent in this species. The spores of S. ochroalba are also thicker than those of North American angiosperm-dwelling species apart from S. aff. futilis. Resemblance to the Eurasian conifer-dwelling S. cummata is strong both in phenology and microscopic structure.

Polyporus semipileatus Peck, Annual Report on the New York State Museum of Natural History 34: 43 (1881).

U.S.A. New York: Catskill Mountains, Acer spicatum, Aug 1880 Peck (BPI 220657 ISOTYPE, designated here). MycoBank No. MBT381253

U.S.A. New York: Essex County, Huntington Wildlife Forest, Betula sp. (branch), 15 Aug 2012 Miettinen 15536 (H 7008664, designated here, duplicate in BPI). MycoBank No. MBT381348

Basidiocarps annual; resupinate to half-resupinate; hard when dry, breaking apart neatly; resupinate basidiocarps up to 10+ cm wide; pilei nodulous to shelf-shaped, often laterally fused, up to 4 mm thick and protruding up to 1.5 cm, sometimes rather fleshy but often thin and sharp-edged with slightly incurved margin or with narrow, sterile ridge on the underside; upper surface slightly rough, matted, white to cream coloured when young, turning ochraceous and finally blackish with age; pore surface cream coloured with ochraceous or rarely faint salmon coloured tints, often a greenish-grey or turquoise tint emerges within the tubes particularly in the pileate part, sometimes in scattered blotches; context and subiculum coriaceous, white; context sometimes faintly zonate in longitudinal section; tube layer up to 2 mm thick; pores (7–)8–9(–11) per mm.

Hyphal structure: skeletal hyphae in context / subiculum (1.0–)2.0–3.3(–4.3) µm wide, in trama (1.0–)2.0–3.9(–5.0) µm wide, generative hyphae in trama 1.0–2.1(–3.0) µm wide.

Basidiospores (2.3–)2.8–3.1(–3.3)×0.4–0.6(–0.7) µm, L=2.97 µm, W=0.55 µm, Q’=(4.1–)4.7–7.0(–7.5), Q=5.43, n=450/15.

Temperate holarctic, extending to south-boreal zone at least in Fennoscandia; on various angiosperm species, often on thin fallen branches but sometimes on coarse wood as well.

FINLAND. Uusimaa: Helsinki, indet. angiosperm (fallen branch), 9 Oct 2011 Miettinen 14917.4 (H); Kirkkonummi, Prunus padus (fallen tree), 24 Oct 2012 Miettinen 15835 (H). Etelä-Häme: Hämeenlinna, Lammi, Corylus avellana (fallen branch), 11 Sep 2002 Miettinen 6694 (H); Pohjois-Häme: Jyväskylä, Vuoritsalo, Juniperus communis (fallen trunk), 15 Jul 2017 Miettinen 21003 (H). NORWAY. Møre og Romsdal: Nesset, Ulmus glabra, 22 Sep 2006 Ryvarden 47279 (O 361851); Sogn og Fjordane: Luster, C. avellana, 25 Aug 2007 Gaarder 5136 & Dybwad (O 293503). POLAND. Podlaskie Voivodeship: Hajnówka, C. avellana, 18 Sep 2012 Korhonen 76 (H). RUSSIA. Khabarovsk Reg.: Khabarovsk Dist., Ilga, Actinidia kolomikta, 10 Aug 2012 Spirin 5142 (H); Nizhny Novgorod Reg.: Lukoyanov Dist., Sanki, C. avellana, 7 Aug 2005 Spirin 2326 (H). UNITED KINGDOM. Scotland: South Lanarkshire, P. padus (fallen tree), 6 Jul 2010 Miettinen 14114 (H). U.S.A. Massachusetts: Holden, Betula sp. (fallen branch), 6 Sep 2013 Miettinen 16823 (H); Minnesota: Waseca, Tilia americana (fallen branch), 18 Aug 2013 Miettinen 16693.1 (H); New York: (lectotype, see above); (epitype, see above); indet. angiosperm wood, 18 Aug 2012 Miettinen 15715 (H); Betula sp., 22 Sep 2013 Miettinen 17135 (H); Fagus grandifolia (fallen tree crown), 20 Sep 2013 Miettinen 17074 (H).

S. semipileata seems to be the most widespread species in the S. nivea complex and overlaps with many of the other angiosperm-dwelling species: in Europe with S. futilis and S. nemoralis; in the Far East with S. lepida and S. nivea; and in North America with S. aff. futilis and possibly with S. calida. Apart from S. (aff.) futilis, these species are almost impossible to distinguish from each other morphologically.

China. Yunnan: Xishuangbanna, Xishuangbanna Biosphere Reserve, alt. 700 m, indet. angiosperm wood, 5 Aug 2005 Miettinen 10002 (H 7008668, isotype BJFC).

Basidiocarps annual; half-resupinate; small, up to 1 cm wide and 1 mm thick; hard when dry but easy to break apart; pilei thin, protruding up to 4 mm; margin incurved; upper surface minutely rough, matted, white to cream coloured when young, turning ochraceous; context up to 0.7 mm thick, azonate; tube layer up to 0.3 mm thick; pores 7–9 per mm.

Hyphal structure: skeletal hyphae in context 1.0–2.9(–3.5) µm wide, in subiculum (1.0–)2.0–2.9(–3.2) µm wide, in trama 2.0–4.0(–4.8) µm wide, generative hyphae in trama 1.0–1.9(–2.0) µm wide.

Basidiospores 2.9–3.2(–3.3)×(0.4–)0.5–0.6(–0.7) µm, L=3.04 µm, W=0.55 µm, Q’=(4.6–)4.8–6.4(–7.5), Q=5.49, n=30.

The species is known only from the type specimen, collected from Yunnan, China, where it was growing as small individual pilei on thin twigs of unidentified woody angiosperm.

Derived from unguis (Lat.), claw, nail; refers to nail-like basidiome caps.

CHINA. Yunnan: (holotype, see above).

China. Yunnan: Xishuangbanna, Menglun, alt. 640 m, indet. angiosperm wood, 4 Aug 2005 Miettinen 9950 (H 7008660, isotype BJFC, strain FBCC 1132).

Basidiocarps annual; resupinate to half-resupinate; small, up to 2.5 cm wide and 3 mm thick; hard when dry but easy to break apart; pilei nodulous, protruding up to 3 mm; margin blunt; upper surface minutely rough, matted, white to cream coloured when young, turning ochraceous; pore surface cream coloured with yellowish to ochraceous tints; context up to 2.7 mm thick faintly zonate in longitudinal section with fuzzy, ochraceous lines separating layers of growth; tube layer up to 0.3 mm thick; pores 8–10(–11) per mm.

Hyphal structure: skeletal hyphae in context / subiculum 1.0–2.9(–3.8) µm wide, in trama (2.0–)3.0–4.0(–5.1) µm wide, generative hyphae in trama 1.0–2.0(–2.2) µm wide.

Basidiospores (2.7–)2.8–3.1(–3.2)×(0.4–)0.5–0.7 µm, L=2.96 µm. W=0.59 µm, Q’=(4.0–)4.1–6.0(–7.2), Q=4.99, n=90/3.

The species is known from three specimens from Yunnan, China, collected from twigs of unidentified woody angiosperm.

In honour of the Chinese polypore researcher, Prof. Yu-Cheng Dai.

CHINA. Yunnan: (holotype, see above); Xishuangbanna Biosphere Reserve, alt. 700 m, indet. angiosperm wood (dead standing tree), 9 Aug 2005 Miettinen 10150.2 (H); Xishuang Banna Primeval Forest Park, indet. angiosperm wood (fallen branch), 16 Aug 2005 Miettinen 10366.1 (H).

U.S.A. Maine: Piscataquis Co., Medford, Camp Sunday, on dead Populus, 28 Aug 1905 Murrill (NY, studied).

U.S.A. Maine: (holotype, see above)

P. hymeniicola is a poorly known species from North America which has sometimes been associated with the S. nivea complex (P. semipileatus by Lowe (1947, 1966)). Niemelä (1998) studied the type specimen and concluded that the dimitic trama with solid skeletal hyphae does not match with the S. nivea complex. Even though we have observed some specimens of S. nivea with such hyphal structure, they were not observed in North American material. Furthermore, the basidiocarp of the type specimen grew on a dead basidiocarp of another polypore species, unlike any of our studied material of the S. nivea complex. The species would appear to be related to S. stellae and related species (Incrustoporia).

Australia. Tasmania: Hobart, Rodway (BPI 301712).

Cunningham (1950) mentions the name P. alboniger as the label of a herbarium specimen he determined to be P. atromaculus (see below). We consider the name to be invalid as it lacks proper description (ICBN Melbourne Art. 38.1 & 39.1).

Australia. Tasmania: Hobart, Rodway (BPI 302037).

Cunningham (1965) considered P. atromaculus to be a synonym of S. nivea (or Tyromyces chioneus, as he called it). The name refers to Tasmanian collections of L. Rodway. Lloyd (1922) used the name P. atromaculatus in reporting his determinations to Rodway. Referencing Lloyd (1922), Stevenson and Cash (1936) published Polyporus atromaculus Lloyd in herb. accompanied by a description and specification of a type specimen in a list of fungus names proposed by Lloyd. It is doubtful whether their intention was to validate the name but the description remains invalid (ICBN Melbourne Art. 39.1) and we reject the name. Ryvarden (1990) appears to share this view as he does not include P. atromaculus in his type studies of Polyporus species described by Lloyd.