February 2023 State of LA Fungi
Tuesday, February 28th at 6:30 p.m.
Online discussion using Zoom for paid members
Discussion Leader: Rudy Diaz
Program: "Discussion of the mushroom habitat in the Los Angeles area"

In this virtual meeting we discussed first principles in recognizing fungi, taxonomy and identification in Amanita, and recent findings on the biology of the invasive death cap (Amanita phalloides) in California.

To identify a mushroom is to engage in a scientific activity; the name you apply is your hypothesis. Precise and consistent language enables the communication of specific scientific hypotheses. In the recognition of species, technical language is used for taxonomically-informative trait variation. As such, engaging in active observation and note-taking with mycological terminology (links in the slides) will help you in identification, as well as make you a more careful and curious observer. Procedures for documenting and collecting fungi can be found in the February edition of the Spore Print (here).

There are still a number of Amanita spp. that you can find fruiting in live oak woodland. This is a charismatic group of fungi that has appeared in popular mushroom imagery for centuries, but it also contains some of the most deadly mushrooms in the world. Hence, it is best you familiarize yourself. We discussed the primary characteristics for distinguishing species and taxonomic groupings of the genus Amanita, summarized in Fig. 1 by Bethany Beech of the New York Mycological Society. Importantly, when you encounter an Amanita, it's advised that you dig up the entire mushroom without breaking the base. This is because the morphology of the volva is critical in identification. We then practiced identifying an Amanita using the dichotomous key in David Arora's Mushrooms Demystified.

Lastly, we discussed recent work out of Anne Pringle's lab, which reports a new discovery that changes our thinking on the reproductive biology of mushroom-forming fungi, and gives new insight on how the deadly and invasive Amanita phalloides has expanded its range in California so rapidly. The typical life history of fungi in Basidiomycota involves the union of two separate mycelia belonging to genetic individuals with complementary mating types. After the underground fusion of these mycelia (creating a dikaryon), they form a sexual reproductive structure a mushroom when environmental conditions are favorable. However, using population genomics approaches, the researchers find evidence that Amanita phalloides is also capable of sexual reproduction by single individuals (homokaryons), apparently bypassing the typical genetic controls for mating type compatibility. Mushrooms produced by homokaryons contain aberrant numbers of spores on their basidia, which is morphological evidence of atypical meiosis. However, spores produced by homokaryons can still reproduce normally with spores produced from dikaryons. This biological flexibility to reproduce both bisexually and unisexually is the likely cause of the death cap's success as an invasive species in California.

Rudy Diaz
Resident Mycologist,
Los Angeles Mycological Society

Photo: weevelknievel in the UCR Botanic Gardens
Myriostoma sp.
Observation on iNaturalist
click on image for larger view
Figure 1. The primary characteristics for distinguishing species and taxonomic groupings of the genus Amanita.
click on image for larger view