Hypoxylon taxa are saprophytes of angiospermous plants. Known
taxa are restricted to woody dicotyledons, while a few tropical taxa are known from monocotyledons,
especially bamboo. Some of them are highly host specific but most of them are
plurivorous, and most of commonly encountered trees and shrubs are
hosts for Hypoxylon. It is noteworthy that, in our region,
Hypoxylon was never found on some common woody plants such
as Buxus sempervirens, Euonymus latifolia, Robinia pseudoacacia,
Sambucus nigra, on which other Pyrenomycetes are not uncommon.
These observations might be refuted by observations from other areas, as, for instance, a collection of
on Sambucus nigra reported from western France
(Leroy & Surault, 1999). Two recent
collections of H. julianii
and H. perforatum on Robinia likewise show this tree a possible
host for Hypoxylon.
They appear to be mostly weak pathogens with high saprophytic capacity
(Ju & Rogers, 1996), and
many species proved to grow endophytically in a wide range of various hosts without producing
(Petrini & Petrini, 1985).
or H. cohaerens developing rapidly on killed wood of
at least a latent infection of the host by the fungus
(Chapela & Boddy, 1988a; 1988b). Dying branches of Fraxinus
are soon invaded by
H. cercidicolum or
H. intermedium before
they fall onto the ground, as does
H. laschii on Populus,
but the pathogen role of these species remains obscure.
Where to collect Hypoxylon?
All European Hypoxylon species are active saprophytes
depending mostly upon humidity. They grow on bark or decorticated wood of trunks or branches
lying on the ground in coombs, in alluvial forests, on the banks of streams or rivers,
in damp woods, usually in shadowy places. Some species can grow
on branches still attached to the tree or broken branches hanging
above the soil level, but always in locations with a high and rather
constant level of humidity
of the atmosphere. Low temperatures favour a few species known to
have boreal or hemiboreal distribution, which will be found in mountains
or northern regions of Europe. Most of Hypoxylon prefer mild
temperatures and humidity that they rather find in regions of western
Europe under oceanic influence.
When to collect Hypoxylon?
They develop slowly in natural conditions, needing several
months (usually 3-6) from the formation of the first coloured stromatal
tissue or anamorph on the surface of the substrate to the maturation
of stromata with ascigerous perithecia. A too long period
of drought is frequently fatal to their development. Low temperatures
encountered during winter for short periods apparently only stop or
slow down the development of
Hypoxylon taxa that have started in autumn, but apparently
do not kill them. Therefore Hypoxylon taxa can be found
throughout the year, providing that their substrate remained without
long interruption in a humid enough environment, with more favourable
periods in summer and autumn.
Most of them are perennial, at least for a few following years.
In favourable conditions, it is not rare to find the anamorph or
young stromata growing close to hardly mature stromata appeared
a few months ago.
Some taxa are frequently found growing associated on the same
substrate, for instance
H. carneum and
on rotten wood or
H. petriniae and
H. rubiginosum on a same branch
of Fraxinus. Nethertheless, all species usually grow solitary
and no association between Hypoxylon taxa appears obligatory.
These associations are rather a challenge to field taxonomists!
Ecology of Hypoxylon remains poorly known, and above data
need to be completed, corroborated or refuted by observations from other regions