Darkera
Darkera H.S. Whitney, J. Reid & Piroz., Can. J. Bot. 53(24): 3052 (1975)
Leotiomycetes, Leotiomycetidae, Phacidiales, Phacidiaceae
Foliicolous, occurring on needles of coniferous hosts, such as Abies balsamea, Picea glauca, P. engelmanni, P. excels, Pseudotsuga menziesii. Sexual morph: Apothecia black, solitary to gregarious, or confluent, subhypodermal, immersed to semi-immersed, then becoming erumpent, ellipsoid to elongate, unilocular, glabrous, ostiole absent, opening by a median longitudinal slit and raising the overlying host tissue on both sides of the central fissure. Peridium composed of textura angularis with thick-walled and brown to pale brown cells. Hamathecium consisting of paraphyses and asci. Paraphyses hyaline, numerous, slender, with occasionally slightly swollen and obtuse apex, septate, anastomosing, branched, without sheath, or enveloped by a thin mucilaginous sheath. Asci bitunicate, fussitunicate, with an ocular chamber, 8-spored, clavate to broadly clavate, sessile or sometimes with short or broadly short-cylindrical pedicel, lacking pore structure, releasing ascospores by apical wall irregularly rupturing. Ascospores hyaline to pale brown, or pale brown to olivaceous brown, uniseriate or biseriate, or irregularly arranged, rounded or broadly ellipsoidal, subreniform or allantoid, sometimes slightly tapering with rounded ends, unicellular, smooth-walled or with bright, crack-like decorations on the surface. Asexual morph: Conidiomata brown to dark brown, pycnidial, amphigenous, epiphyllous or hypophyllous, solitary to gregarious or confluent, subepidermal, deeply immersed, raising the epidermis into brown swellings, then piercing it by a lateral neck, globose to subglobose, unilocular, glabrous, thick-walled, ostiolate. Ostiole single, cylindrical to subcylindrical, laterally or centrally located. Conidiomatal wall composed of thick-walled, pale brown to hyaline cells of textura angularis to textura porrecta, textura intricata or textura epidermoidea cells. Conidiophores arising from the innermost layers of conidiomata, reduced to conidiogenous cells, or occasionally present, hyaline, subcylindrical, unbranched, septate, with or without constriction at septa. Conidiogenous cells hyaline, holoblastic or enterolastic, phialidic or annellidic, cylindrical to subcylindrical, ampuliform to lageniform, determinate or indeterminate, discrete or integrated, smooth-walled, with or without proliferation. Conidia hyaline, subcylindrical, or cylindrical to clavate, with a rounded apex, and narrow and truncate base, sometimes bulging in the middle, bearing a widely flared, or funnel-shaped to irregular, undulated, mucoid, apical appendage resulting from the eversion of a mucoid sheath enveloping the upper part of developing conidium.
Type species: Darkera parca H.S. Whitney, J. Reid & Piroz., Can. J. Bot. 53(24): 3053 (1975)
Notes: The genus Dakera was introduced by Whitney et al. (1975) to accommodate D. abietis H.S. Whitney et al. and D. parca. The detailed taxonomy of Dakera has been discussed by Whitney et al. (1975). The asexual morph of Dakera has been assigned to tiarosporella-like species based on host association, but this connection has never been confirmed via culture studies. Crous et al. (2015b) regarded this link as probably correct, because tiarosporella-like morphs have been linked to more than one species (Whitney et al. 1975). A group of fungi share similar morphology with Tiarosporella paludosa (Sacc. & Fiori) Höhn., but cluster to the Phacidiaceae Crous et al. (2015b). Five species are accepted in the genus, D. abietis, D. durmitorensis (Karadžić) Crous, D. parca, D. picea H.S. Whitney et al. and D. pseudotsugae (H.S. Whitney, J. Reid & Piroz.) Crous. In this study, two specimens collected from Italy on dead needles of Picea excelsa Wender. (Pinaceae) correspond very well with D. picea in morphology and phylogeny. These two collections are regarded as conspecific with D. picea. Since no photo of conidiomata structure from nature was given in Crous et al. (2015b), we provide a plate and detailed description for D. picea. In addition, we re-examined the type specimen of both sexual and asexual morphs of D. abietis and D. parca as well as D. pseudotsugae. Of interest is that Dakera species has more than two kinds of conidiomatal wall, viz. textura intricata to textura porrecta, textura epidermoidea or textura angularis, and these kinds of wall cells are often mixed together. Whereas, Tiarosporella species only have textura angularis to textura prismatica wall cells. This apparent difference may be a valuable character to distinguish Dakera from Tiarosporella. Further collections are needed to epitypify and to confirm the placement of Dakera species.
Distribution: Canada, Finland, Norway, Siberia, Switzerland (Crous et al. 2015b, this study).
References:
Li WJ, McKenZie EHC, Liu JK, Bhat DJ, Dai DQ, Caporesi E, Tian Q, Maharachcikumbura SSN, Luo ZL, Shang QJ, Zhang JF, Tangthirasunun N, Karunarathna SC, Xu JC, Hyde KD (2020) Taxonomy and phylogeny of hyaline-spored coelomycetes. Fungal Diversity 100: pages279–801.
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