Castellanea pakaraimophila
Castellanea pakaraimophila T.W. Henkel & M.E. Sm., in Smith et al., IMA Fungus 6(2): 310 (2015)
Etymology: Pakaraimaea and –philus (Gk.) = loving; in reference to occurrence of the species as basidiomata and mycorrhizas with Pakaraimaea dipterocarpacea.
Diagnosis: Differs from other known sequestrate taxa by the combination of the grey-orange to orange-brown peridium, brown unchanging gleba, basidiospores that are often dextrinoid and released in tetrads, and absence of cystidia.
Basidiomata irregularly flattened-ovate, 7–12 mm tall, 12–16 mm broad, subfirm, softer with age; surface light greyish orange (5A5–5B5–5B6) to orange-brown (7C8–7D8–7E8) with occasional darker humic stains, unchanging with pressure, glabrous macroscopically, under hand lens a dense repent mat of light orange hyphae, with age viscid to nearly glutinous; base subtended by a short, concolourous stipe, this 1.5 × 1.5 mm, with a single concolourous hyphal cord. Peridium in longitudinal section extremely thin over apical ¾ (< 0.25 mm), concolourous with the surface, over basal ¼ thickening to 0.75 mm and there off-white, single-layered, separable. Gleba dark brown (6E7–6F7, 7E7–7F7) throughout, unchanging with exposure, of irregularly shaped locules with interior surfaces minutely brownish hispid under hand lens; locule walls translucent-gelatinous; columella arising from the thickened basal peridium, with a single narrow gelatinous vein extending to apex. Odour slightly of iodine; taste not obtained. Macrochemical reactions not obtained.
Peridium 25–190 μm thick, single-layered, of tightly interwoven, repent hyphae, yellowish brown in KOH and H2O, becoming more parallel and hyaline toward gleba; individual hyphae 2–5 μm wide, thin-walled; terminal cells cylindrical to subcapitate, 19–36 × 2–3 μm. Glebal trama with a distinct mediostratum and lateral stratum; mediostratum hyaline in H2O and KOH, 12.4–29.6 μm wide, of parallel, slightly interwoven hyphae; individual hyphae 2–8 μm wide; lateral stratum divergent at a right angle from mediostratum, hyaline in H2O and KOH, grading imperceptibly into the densely interwoven subhymenium. Hymenium a palisade of tightly packed basidia and basidioles. Basidia faintly grey in H2O and KOH, changing in shape with maturity; in developing basidiomata (e.g. Henkel 9670) subclavate, infrequently cylindro-clavate, rarely cylindrical, 36–54 μm long, 6.0–12.5 μm broad at apex, 5.0–11.5 μm at centre, 5.0–8.5 μm at base, thin-walled; sterigmata four, straight, 4–7.5 × 0.9–1.5 μm; in fully mature basidiomata (e.g. Henkel 9514) consistently clavate, 20–25 μm long, with four short (∼1 μm), highly reduced sterigmata. Basidiospores statismosporic, smooth, subfusiform, bilaterally symmetrical in all views, 12–18 × 5.5–8(–10) μm (mean = 14.7 ± 1.20 × 7.1 ± 0.91 μm; Qr = (1.5–)1.9–2.7, Qm = 2.1 ± 0.25; n = 61), light yellowish brown in H2O and KOH, often with one dextrinoid guttule, with a short pedicel ± l μm long, frequently released in tetrads. Cystidia and clamp connections absent.
Habit, habitat and distribution: Solitary or in a small group partially emergent on mineral soil/humic layer interface on the forest floor under P. dipterocarpacea, or immersed in decaying wood humus at base of dead P. dipterocapacea; known only from the type locality in the Upper Mazaruni River Basin of Guyana.
Index Fungorum number: IF812362
Notes: Castellanea pakaraimophila is recognized in the field by the ovate basidiomata, orange-brown peridium, dark brown loculate gleba, short stipe, unchanging tissues upon exposure, and association with P. dipterocarpacea. Micromorphologically C. pakaraimophila is characterized by the smooth, yellowish brown, frequently dextrinoid basidiospores that abscise in tetrads, and well-defined mediostratum of the glebal trama. Castellanea pakaraimophila has been confirmed as an ECM symbiont of P. dipterocarpacea based on analysis of ITS rDNA sequences from ECM roots (Smith et al. 2013). In the phylogenetic analysis reported here, C. pakaraimophila is putatively related to a cluster of Tylopilus species, including the type species of the genus T. felleus, but without bootstrap support (Figure 1).
Castellanea pakaraimophila is similar to Mackintoshia persica because both have dextrinoid or partially dextrinoid, light yellowish brown or ochraceous-yellow basidiospores (Castellano et al. 2000, Pacioni & Sharp 2000). However, C. pakaraimophila differs from M. persica in its subfusiform basidiospores released in tetrads and lack of cystidia (Pacioni & Sharp 2000). Additionally, the glebal trama in M. persica ranges from 200–330 μm wide, is gelatinous, and lacks a distinct mediostratum. The protologue description of M. persica notes that basidium morphology changes with basidioma age in a manner similar to that seen in C. pakaraimophila (Pacioni & Sharp 2000). However, with C. pakaraimophila the basidia become smaller and more angular with age, whereas the initially clavate basidia of M. persica become long-utriform to fusiform (Pacioni & Sharp 2000). The two species are also unrelated phylogenetically (Figure. 1).
Some Rossbeevera species can nominally resemble C. pakaraimophila because they have nearly smooth basidiospores and lack cystidia. However, the basidiospores of Rossbeevera are non-dextrinoid, individually abscised, slightly to distinctly longitudinally ridged, and barely angular to stellate in polar view. In contrast, the dextrinoid basidiospores of C. pakaraimophila lack angularity and are frequently abscised in tetrads. Basidiomata of Rossbeevera species also undergo a blue or blackish colour change upon bruising or exposure (Lebel et al. 2012, Orihara et al. 2012b).
Based on the basidiome colour and basidiospore shape, C. pakaraimophila bears some resemblance to species of Alpova (Paxillaceae) and Mycoamaranthus (Boletaceae). However, Alpova species have smaller basidiospores, a pseudoparenchymatous peridium, abundant clamp connections, and are usually associated with Alnus (Dodge 1931, Nouhra et al. 2005, Moreau et al. 2011, Moreau et al. 2013, Hayward et al. 2014). Species of Mycoamaranthus, though similar in peridial micromorphology to C. pakaraimophila, have finely ornamented to spinulose basidiospores, a bright yellow peridium, and are currently only known from Africa, South-East Asia, and Australasia (Castellano et al. 2000, Lumyong et al. 2003). The fusoid, smooth, pedicellate basidiospores of C. pakaraimophila also resemble those of species of Hysterangium (Hysterangiales) which otherwise differ in having a dendroid columella, a dark greenish or brown gleba, and in lacking cystidia (Castellano et al. 1989).
Species in a few other temperate sequestrate genera of Boletales have large, fusoid, smooth basidiospores that could potentially be confused with those of C. pakaraimophila, but differ, in addition to having non-dextrinoid basidiospores, in the following ways: Melanogaster species have a black gleba with gel-filled locules; Rhizopogon species have olivaceous to dark brown gleba colours and are associated with Pinaceae; and Truncocolumella species have greenish brown gleba colours, a dendroid columella, and are associated with Pinaceae (Trappe et al. 2009).
Figure 1. Maximum likelihood (ML) phylogram (-ln = 57979.037507) based on RPB1, RPB2, and 28S ribosomal DNA sequences depicting phylogenetic relationships of the Boletaceae and new sequestrate Guyanese taxa (in red bold). ML bootstrap support values greater than 70 are shown above the nodes. Other sequestrate taxa are indicated in bold with solid black dots preceding their binomials. Previously identified clades with multiple species from the same higher taxon are collapsed into triangles for visual simplification as is a clade of outgroup taxa from several non-Boletaceae lineages of Boletales.
Figure 2. Basidiomata of Castellanea pakaraimophila. A. Dorsal view (left) and ventral views (middle, right) showing short stipe (holotype; Henkel 9514). B. Longitudinal section showing highly folded gleba, basally thickened peridium, and short stipe (Henkel 9670). C. Orangish brown peridium (Henkel 9670). Scale bars = 10 mm.
Figure 3. Microscopic features of Castellanea pakaraimophila (holotype; Henkel 9514). A. Basidiospores. B–C. Four-sterigmate basidia with mature basidiospores. D. Glebal trama showing distinct mediostratum and strongly diverging lateral stratum. B–C = phase contrast. Scale bars = 10 μm.
Key reference:
Smith, M. E., Amses, K. R., Elliott, T. F., Obase, K., Aime, M. C., & Henkel, T. W. 2015. New sequestrate fungi from Guyana: Jimtrappea guyanensis gen. sp. nov., Castellanea pakaraimophila gen. sp. nov., and Costatisporus cyanescens gen. sp. nov. (Boletaceae, Boletales). IMA fungus, 6(2), 297–317.
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