Species has always been a slippery concept, and DNA sequencing—despite its precision—has not made it easier to handle. Classically, species boundaries were defined by the inability of individuals on each side to mate and produce fertile offspring. That’s easy enough to figure for horses and donkeys. (They mate but do not produce fertile offspring.) But what about fungi?

— mushroom-eowch. 17

I remember the discussion vividly: I was at the edge of my seat. Dr. Suzuki was treating species in the way cultural anthropologists treat their units: as frames that must be continually questioned to retain their use. The kinds we know, he implied, develop at that fragile junction between knowledge-making and the world. Kinds are always in process because we study them in new ways. This makes them no less real, even as they seem more fluid and beckoning of questions.

— mushroom-eowch. 17

(emphasis added)

tl;dr: fungi defy our definitions of species, incorporating genetic material from other fungi, from bacteria, etc. species start to make sense only relatively, making the clean divisions of the old taxonomic approach seem Platonic in comparison.

Ignatio Chapela, a forest pathologist at the University of California, Berkeley, was even more adamant that the idea of “species” limits the stories we can tell about kinds. “This binomial system of naming things is kind of quaint, but it is a complete artifact,” he told me. “You define things with two words and they become an archetypal species. In fungi, we have no idea what a species is. No idea. ... A species is a group of organisms that potentially can exchange genetic material, have sex. That applies to organisms that reproduce sexually. So already in plants, where out of a clone you can have change as time goes by, you have problems with species. ... You move out of vertebrates to the cnidarians, corals, and worms, and the exchange of DNA, and the way groups are made, are very different from us. ... You go to fungi or bacteria, and the systems are completely different—completely crazy by our standards. A long-lived clone can all of a sudden go sexual: you can have hybridization in which whole big chunks of chromosomes are brought in; you have polyploidization or duplication of chromosomes, where a completely new thing comes out; you have symbiotization, the capture of, say, a bacterium that allows you to either use the whole bacterium as part of yourself or use parts of that bacterium’s DNA for your own genome. You’ve become something entirely different. Where do you break down the species? 9 ”

To compare different kinds of matsutake, Dr. Chapela used herbarium specimens as well as fresh samples and sequenced ITS-region DNA. But he refused to imagine his results as fixed species. “You start getting these groupings that you can only name relative to each other. You can’t call them a species. ... In the old taxonomic approach you say, ‘this is my ideal’—it’s completely Platonic—and everything is going to compare as a missed approximation to that ideal. Nobody will be the same as this, but you compare and see how close they are to this ideal. ... If it becomes too different—by whatever measure, and the measures are completely arbitrary—you say, ‘oh this must be a different species.’ ” To avoid a false “scientific cover,” he speaks of “matsutakes” as all the varied kinds that enter the Japanese trade. His study did, however, find distinct genetic groupings by region. That means, he said, that genetic materials are not freely exchanged across those regions. “If you see good patterning, if you see good separation, that tells you that there is not much exchange between these groups.” These data show that cross-regional exchange of spores is unlikely on a regular basis.

— mushroom-eowch. 17

truth-and-lies