Cryptic species diversity in polypores: the Skeletocutisnivea species complex
Author
Korhonen, Aku
Author
Seelan, Jaya Seelan Sathiya
Author
Miettinen, Otto
text
MycoKeys
2018
36
45
82
http://dx.doi.org/10.3897/mycokeys.36.27002
journal article
http://dx.doi.org/10.3897/mycokeys.36.27002
1314-4049--45
Skeletocutis nivea
complex
Description.
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. 5
C-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
Niemelae
(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. 6
A-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 (
Niemelae
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. 6
E-G
) (5
-)6-9(-
10)
x(2.2-)2.7-3.7(-
4)
µm
wide, tetrasterigmatic.
Basidiospores (Fig. 7) narrowly allantoid, 2.5
-4.0x0.4-
0.9
µm
,
Q'=3.4-
7.0, IKI-, CB- (contents CB+).
Figure 7. Spores of selected species in the
Skeletocutis nivea
complex.
Discussion.
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
Niemelae
(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.