December 2022 State of LA Fungi
Monday, December 27th at 6:30 p.m.
Online discussion using Zoom
Discussion Leader: Rudy Diaz
Program: "Discussion of the mushroom habitat in the Los Angeles area"

It's happening... The storms have anointed the chaparral and live oak woodlands with a mushroom season of historic abundance. In addition to what's turned out to be the year of the jack-o-lantern (Omphalotus olivascens), species seldom documented in the past have made themselves more visible. Go out and explore.

Slides from the presentation.

We went over some first principles for identifying fungi. Most importantly, recognize that if you can see the fungus, you are most likely encountering it in the reproductive stage of its life history. Mode of sexual spore production is the primary distinction for the two major lineages of fungi with macroscopic fruiting bodies – Ascomycota and Basidiomycota. Together, they represent the "crown" group of the fungal kingdom, Dikarya.

We went through the steps for identifying a fungus with tiny, carbonaceous, boat-shaped sexual structures (hysterothecia), starting with a key for major form groups ("The Wheels” from Fungi of Temperate Europe), then moving on to finding specialist literature and interpreting your microscopy against a dichotomous key and mycological glossary. We determined that the fungus is a close match for Hysterobrevium smilacis (Hysteriales, Dothideomycetes, Ascomycota).

Useful resources for interpreting taxonomic literature are the illustrations from Snell and Dick (1957, click here) and Kellerman's Mycological Glossary (1905).

We discussed some recent finds from the desert, and the careful observation necessary to spot the lifted tiles of dried mud that may indicate a mushroom's emergence. Many desert fungi exhibit a gasteroid morphology, such as Disciseda spp. (Agaricales, Basidiomycota) and Carbomyces spp. (Pezizales, Ascomycota). Both of these genera are poorly studied and represented by only a few collections. Fortunately, Dave G. has been making a focused effort to document them and share with us his findings.

Desert fungi are also represented by a great diversity of so-called "stalked puffballs." Many of these belong to the genus Tulostoma (Agaricales, Basiodiomycota), although the group is not strictly confined to the deserts. We discussed how the true species diversity of Tulostoma has only recently come to light, but distinguishing most of them would require examination of spore ornamentation with an electron microscope or DNA sequencing. So don't count on getting your Tulostoma observations to species so easily.

That said, the growing accessibility of DNA barcoding technologies have allowed us to start recognizing that a great number of West Coast mushrooms which have historically gone by the same names as East Coast or European species (with which they bear superficial resemblance) should actually be recognized as species in their own right. Stu Pickell, LAMS Vice President, shared with us some of these recent discoveries after sequencing some collections with Alan Rockefeller. These include an Omphalina sp. (Omphalinaceae, Agaricales), which has previously been misidentified in the region as Contumyces rosellus (Repetobasidiaceae, Hymenochaetales); a Pholiota sp. (Strophariaceae, Agaricales), which shows close relation to P. mixta; and a Gyrodon sp. (Paxillaceae, Boletales), which is a close match for a collection sequenced from Mexico, but still undescribed.

One may start to wonder, why should mushrooms that bear strong morphological resemblance be divided into separate species? Well, appreciating that the fungal habit is mostly microbial (consisting of chemical interactions between hyphae and the environment), it becomes apparent how populations of mushrooms could accumulate high levels of dissimilarity in genetic features while maintaining high levels of similarity in macroscopic features. For example, in addition to Tulostoma spp. looking similar, they also inhabit similar environments. However, there is now evidence to suggest that while some species are saprotrophs, others rely on nutrient exchange with living biotrophic partners. This ecological distinction is not at all apparent by just observing these fungi in situ. Their biotrophic partners have still not been identified.

Furthermore, in contrast to a view that origin and diversification of new species results from adaptation to novel environments (epitomized by the common story of Darwin's finches), prolonged geographic isolation is all that is necessary for populations to diverge enough in their genetic composition such that they can no longer reproduce. This argument is advanced for vertebrates in a recent publication by Anderson and Weir in Science, and has made a splash in evolutionary biology. However, those who know fungi have had this intuition for a long time.

Rudy Diaz
Resident Mycologist,
Los Angeles Mycological Society