Pararhexoacrodictys Cantillo & Gusmão, 2019
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publication ID |
https://doi.org/ 10.11646/phytotaxa.397.2.8 |
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persistent identifier |
https://treatment.plazi.org/id/039087E9-F72F-325D-FF21-FC98A1150CD7 |
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treatment provided by |
Felipe |
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scientific name |
Pararhexoacrodictys Cantillo & Gusmão |
| status |
gen. nov. |
Pararhexoacrodictys Cantillo & Gusmão View in CoL gen. nov.
Etymology: —para + Rhexoacrodictys similar, closer, related to Rhexoacrodictys
MycoBank: MB824302
Diagnosis: morphologically similar to both Rhexoacrodictys and Pseudoacrodictys , but differing from those genera based on conidiogenous events, and phenotypic features such as conidial pigmentation, septa pattern, appendages and secession.
Description: Colonies effuse, brown to black. Mycelium partly immersed in the substrate, composed of branched, septate, pale brown to brown smooth hyphae. Conidiophores macronematous, mononematous, scattered or in smalls groups of two or three, erect, straight or slightly flexuous, smooth, thick walled, cylindrical, septate, brown to dark brown or nearly black toward the base. Conidiogenous cells monoblastic, integrated, terminal, brown to pale brown, extending percurrently and with a frill following conidial disarticulation. Conidial secession rhexolytic. Conidia holoblastic, solitary, dry, acrogenous, highly variable in shape been from globose to turbinate or irregularly shaped or in some cases nearly palmate or digitate, evenly pigmented, with thin septa than appears to be collapsed or distorted, fainted or vanished in completely developed conidia, possessing pale brown appendages which occasionally collapse at the thin walled apex. Basal cell present, delimited by a transverse septum.
Type species:— Pararhexoacrodictys catolensis Cantillo & Gusmão sp. nov.
Notes: Pararhexoacrodictys is, morphologically, an intermediary genus between Rhexoacrodictys W. A. Baker & Morgan-Jones (2002: 98) (rhexolytic secession) ( Baker & Morgan-Jones 2002a) and Pseudoacrodictys Baker & Morgan-Jones (2003: 373) (schizolytic secession). These three genera have conidiogenous cells with lageniform to doliiform terminal percurrent extensions but they differ in conidial secession, septation and appearance. Compared with Rhexoacrodictys , both genera share the same type of conidial secession but in the last, conidia are obovate to subsphaerical, unevenly brown to dark brown pigmentation or almost black in some cases and lacking appendages; also, it possesses well-differentiated transversal and longitudinal septa, and conidial shape is retained.
Pseudoacrodictys has in common with Pararhexoacrodictys the presence of the appendages, morphology, appearance and the pigmentation of the conidia. In both genera, conidia are evenly pigmented and share same kind of textura angularis given by the septal arrangement in the conidial surface. So, the most important character for delimitation of this genus from Pseudoacrodictys is its rhexolytic conidial secession.The break toward the conidiogenous cell apex occurs at a readily discernible, thin and lightly-pigmented zone just below the basal septum of the conidia ( Fig. 1 H, J View FIGURE 1 ). This is followed by the growth of the inner wall of the conidiogenous cell and the rupture of the periclinal wall at some distance below the septum which remains intact ( Fig. 1 E, I, J View FIGURE 1 ). The lateral walls of the intermediary cell progressively become thinner, fragile, and eventually fracture and disarticulation of the conidia occurs with releasingfragmentation occurring rather irregularly and resulting in a torn appearance given by fragments of the intermediary collapsed cell, which remain attached to both the basal cell and the conidiogenous cell ( Fig. 1 A–D View FIGURE 1 , Fig. 3 A View FIGURE 3 ). This process was described by Baker et al. (2002a) for conidial secession in Rhexoacrodictys , who also considered it as a taxonomical valuable and phylogenetically informative character.
The conidial shape in Pararhexoacrodictys , is more variable than in other genera derived from Acrodictys and in some occasions the conidia collapse resulting in a peel-off appearance. The septa seem to be as superficial in the conidial surface and look as faint, vanished, sometimes even with a wrinkled aspect and clearly differing from other species in Acrodictys s.l. This characteristic allows some confusion with Shrungabeeja V.G. Rao & K.A. Reddy (1981: 109) , which is understandable since both genera have dark colored conidiophores and integrated, monoblastic conidiogenous cells that extend percurrently and solitary conidia with appendages. However, according to the original description ( Rao & Reddy 1981), conidia are aseptate in Shrungabeeja and possess filiform or horn-like, almost straight appendages, seceding schizolytically and also the appendages maintain an intact appearance in all its extension.
Likewise, the reminiscent peel-like outer wall of conidia observed in some conidia in Pararhexoacrodictys is also found in other genera of Dothideomycetes with large conidia as Piricaudilium Holubová-Jechová (1988: 200) , Megacapitula J.L. Chen & Tzean (1993: 347) and Quadricrura Kaz. Tanaka, K. Hiray. & Sat. Hatak. (2009: 196) , but we can easily differentiate those genera from Pararhexoarodictys based in other taxonomic characters. In Piricaudilium the conidiogenous cells are monotretic, inflated and with a distinct dark pore, the conidia have a verrucose to spinulose base and also possess an internal network of branched hyaline hyphae ( Holubová-Jechová 1988). Megacapitula has micronematous conidiophores that could be smooth, roughened or verrucose; conidiogenous cells are determinate and also the large holoblastic conidia have densely packed, hair-like appendages at the apex ( Chen & Tzean 1993); and Quadricrura has monoblastic conidiogenous cell that are indistinguishable from the creeping hyphae, and the conidia have one or two long appendages arising from the apical part and mostly four to five short appendages around the basal sides ( Tanaka et al. 2009).
Another similar genus of uncertain placement, Kalamarospora G. Delgado (2011: 232) also have rhexolytic secession leaving a distinct, usually truncate frill which remains attached to the basal cell of the conidia that are borne on monoblastic percurrently proliferating conidiogenous cells disposed on macronematous, cylindrical, solitary, unbranched, dark brown to blackish brown conidiophores similar to Pararhexoacrodictys . However, conidial appendages in the former are originated internally from a mass of subhyaline filaments arising from suprabasal cells; moreover, conidia differ in shape and appendages are more numerous and longer.
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