Phragmogibbera xylariicola Samuels & Rogerson
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Authority
Samuels, Gary J. & Rogerson, Clark T. 1990. New ascomycetes from the Guayana Highland. Mem. New York Bot. Gard. 64: 165-183.
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Family
Venturiaceae
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Scientific Name
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Description
Species Description - Stromata turbinata, ca. 300 µm alta, 400 µm lata, conidiogena. Conidiophora ad 100 µm Ion ga, 3-5 µm lata, pauci ramosi, percurrenti proliferans. Conidia cylindricae vel anguste clavatae, 25-42 X 7.5-11.2 µm, (l-)2-3-distoseptatae, brunneae. Ascomata globosa, 300-350 µm diam., nonpapillata, nigra, carbonacea, ex sporodochia conidiogena orienta. Asci late cylindrici vel anguste clavati, 125-175 x 12-22 µm, bitunicati, 8-spori. Ascosporae fusiformes, 30-37.5 x 5-7.5 (-10) µm, 3-septatae, versicolorae. Pseudoparaphyses ramosae, septatae, 2.5-3 µm latae. Hab.: In Xylaria ? schweinitzii Berk. & Curt. Holotypus: Venezuela (Samuels 1238, VEN) Anamorph: Stigmina-like Stromata emergent from ostiola of host Xylaria, turbinate, ca. 300 µm high, 400 µm wide. at first a hemispherical, brown head of conidia on a short, black base; ascomata ultimately in groups of 5-7 around the periphery of the base below the conidial hymenium after the cessation
Distribution and Ecology - Venezuela, known only from the type specimen.
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Discussion
TYPE. VENEZUELA. Amazonas: Dpto. Rio Negro, Cerro de la Neblina, Summit Camp 5, valley at N base of Pico Phelps, 00°49'N, 66°00'W, elev. 1000- 1250 m, on Xylaria ? schweinitzii, 12, 13 Apr 1984, Samuels 1238 (holotype VEN, isotype NY).
Notes. Phragmogibbera xylariicola fits Barr's (1987) concept ofthe Venturiaceae in having m edium- sized ascomata, pigmented, septate ascospores, a hamathecium of branching, cellular pseudoparaphyses, and conidia produced holoblastically on percurrently proliferating conidiogenous cells. Phragmogibbera is most closely related to Gibbera Saccardo, a genus characterized by an erumpent hypostroma and no superficial mycelium. Sivanesan (1984) studied several species of Gibbera, demonstrating that ascomata develop within conidiogenous stromata of species of Stigmina Saccardo and Dictyodochium Sivanesan. The aggregate conidioma/ ascoma of species such as G. caffra Sivanesan is anatomically and morphologically similar to P. xylariicola. The presumed anamorph of P. xylariicola can be assigned to Stigmina. It differs from typical members ofthe genus (EUis, 1971,1976) in having long, ffexuous conidiophores that proliferate percurrently at slightly swollen areas to produce entire conidiogenous cells rather than short extensions ofthe conidiogenous locus that give the conidiogenous cell an annellated aspect. A n attempt to germinate ascospores of P. xylariicola on commeal dextrose agar (Difco) at 20°C was not successful, but the juxtaposition of conidiomata and ascomata leave no doubt that these fungi are part of the same life-cycle. Previously known members of the Venturiaceae occur most often as parasites of green plants less frequently as saprobes. Phragmogibbera xylariicola is unusual in the family in being fungicolous. Although we cannot unequivocaUy state that the species is a mycoparasite rather than an inhabitant of effete stromata ofthe Xylaria, the possibility of mycoparasitism seems likely given that there remain numerous, apparently normal ascospores ofthe host Xylaria in the stromata. Very few ascomata with asci and ascospores were found in this material, thus we were not able to describe the manner of ascomatal opening from microtome sections of mature ascomata. The impression given from immature ascomata (Figs. 55, 56) is that opening is likely to be lysigenous through an apical pore. Samuels et al. (1988) did not find a preformed ascomal opening in Gibbera sphyrospermi Samuels, M . E. Barr & Rogerson. Darkly pigmented cells at the surface ofthe ascomatal wall of G. sphyrospermi released a green pigment in K O H . Cells at the ascomatal surface of P. xylariicola become blue-green in K O H.