A molecular and morphological reassessment of Diademaceae

Abstract

We revisit the family Diademaceae based on available sequence data and morphology. Diademaceae is characterized by ascomata opening with a flat circular lid and fissitunicate, short orbicular frequently cylindrical, pedicellate asci. Ascospores are frequently circular in section but narrowing to one end with three or more transverse septa, without longitudinal septa, and mostly with a thick sheath. In recent treatments Clathrospora, Comoclathris, Diadema, Diademosa, and Graphyllium were placed in the family. Following molecular and morphological study, Clathrospora, Comoclathris, and Diademosa, are excluded from the family and referred to Pleosporaceae. Graphyllium is excluded from Diademaceae, based on hysterothecium-like ascomata with a longitudinal opening, and tentatively placed in Hysteriaceae with uncertainty; species with hysterothecia have now been accommodated in at least five families. The study accepts only Diadema in the family. The status of Diademaceae as a distinct family, based on the ascomata opening by a flat circular lid, is thought to be doubtful. Fresh collections of Diadema are needed for epitypification and to obtain sequence data to establish if this is a well-resolved family.

Figure 1

RAxML tree based on a combined dataset of SSU and LSU. Bootstrap support values >50% are shown above or below the branch. The putative strains of Clathrospora elynae (CBS 196.54 and CBS 161.51) and Comoclathris compressa (CBS 157.53 and CBS 156.53) are indicated in red. Dothidea sambuci is the out-group taxon. The original isolate numbers are noted after the species names.

Figure 2

Diadema tetramerum (holotype). (a) Ascomata on substrate opening via a flat circular lid. (b) Vertical section of ascoma. (c) Closeup of the peridium. (d) Hyaline, septate pseudoparaphyses. (e) Apical part of the asci, ((f)-(g)) Asci with short orbicular pedicel. ((h)–(j)) Reddish-brown ascospores with broad sheath. Scale bars: (b) = 100 μm, (c) = 10 μm, ((d)–(g)) = 60 μm, and ((h)–(j)) = 30 μm.

Figure 3

Clathrospora elynae (isotype). (a) Herbarium material. (b) Closeup of ascomata. (c) Section of the ascomata. (d) Closeup of the peridium (e) Hyaline, filiform, and pseudoparaphyses. ((f)–(h)) Cylindrical to clavate asci with a short pedicle and ocular chamber. ((i)–(k)) Dark brown to brown muriform ascospores surrounded by a thin, hyaline mucilaginous sheath. Scale bars: (b) = 100 μm, (c) = 10 μm, ((d)–(g)) = 60 μm, and ((h)–(j)) = 30 μm.

Figure 4

Diademosa californiana (holotype). ((a)-(b)) Ascomata on host substrate. (c) Side view of the ascomata. ((d)-(e)) Section of ascomata. (f) Section of peridium. (g) Septate, hyaline, and cellularpseudoparaphyses. (h) Light to dark brown seta. ((i)–(k)) Ascus with minute pedicel bearing irregularly arranged 8 ascospores. (l)–(n) Ascospores. Scale bars: ((d)-(e)) = 200 μm, ((f)–(h)) = 10 μm, ((i)–(k)) = 50 μm, and (l)–(n) = 10 μm.