Monographs Details: Phragmogibbera xylariicola Samuels & Rogerson
Authority: Samuels, Gary J. & Rogerson, Clark T. 1990. New ascomycetes from the Guayana Highland. Mem. New York Bot. Gard. 64: 165-183.
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, V E N )
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.
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.