I see my fair share of species within the family Xylariaceae here in North America. These saprobic organisms are pretty easy to identify in the forests I frequent. Near the tropics however, there is an exceedingly wide diversity of fantastically shaped stromatic flask fungi within the same family. One genus of interest is Thamnomyces.
Thamnomyces dendroidea. Photo by Susanne Sourell.
Thamnomyces species are characterized by having wiry, black, brittle “fruitbodies.” Like all of the Xylaria species I’m familiar with, these black structures aren’t actually true fruitbodies, but rather, structures known as stromata. Within the stroma, there are several tiny spherical spore-bearing fruitbodies embedded near its outer surface.
The imbedded perithecia within the stroma of Xylaria polymorpha.
Most species in this family have a black base, but early enough in their development produces a white powdery material. Thamnomyces like other Xylaria species actually produce white, asexual spores known as conidia. Later in their development, these white conidia disperse, leaving behind a fully black fungus that has shifted its efforts towards producing sexual spores. Again, those sexual spores are produced in the imbedded perithecia within the stroma.
Thamnomyces dendroidea. Photo by Rich Hoyer.
Competition is fierce for these fungi, both here in temperate North America and near the tropics. The timing of the production and release of both spore types highlights the evolutionary response driven by competition. Early on, these species produce conidia; large spores that germinate into genetically identical individuals. The conidia for these species are not aimed to travel vast distances but instead, help in propagation. The more individuals that germinate on a log, the fewer other species there will be that can potentially compete. Producing conidia early on is a great adaptation that helps the individual propagate readily on this viable substrate. These conidia help these species quickly establish themselves. Once established, these genetically identical species produce their smaller, wider dispersing sexual spores.
Morphological characteristics of Thamnomyces dendroidea. a, b.) Stromatal habit. c.) Fertile stromatal tips. d.) Section through multiperitheciate fertile stromatal tip. e,f.) Micrographs. e Ascospores in ascus. From Stadler et al. 2010.
Producing sexual spores helps maintain genetic diversity in the population and allows for evolutionary adaptations over time. Conidia allow these species to take over a resource quickly which gives them a competitive edge over other saprobic species. I love learning about different fungi with unique forms that are closely related to species I regularly encounter. Comparing these species that live in drastically different habitats, I find it interesting that the timing of spore type production enhances species fitness across these landscapes.
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