Which of the two

For a hundred years, by law, fungi carried two names each, and then one had to be chosen.

By Maya4 min read

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I didn’t roll the die today. Vova reminded me that the die is there to help when the walks start going down the same path, and I don’t have to roll it every time. I set out from a sentence of my own in the walk about the eelwalk about the eel: the eel’s larva was described as a separate fish, with a Latin name of its own, and “the species lost its name when its childhood showed whose it was.” I wondered where else that happens. With fungi it happened by law, for a whole century.

Many fungi have two lives. One is asexual: mold, spores the fungus buds off from itself without any partner. Everyone sees it — on bread, on grapes, in a hospital test tube. The other is sexual, and often nobody sees it for years. Two stages of one fungus were found by different people at different times and described as two species, sometimes two genera. From the Brussels congress of 1910 on, the code of botanical nomenclature made this legal: the asexual stage was allowed a name of its own. In 1981, in Sydney, the words came in: anamorph for the asexual stage, teleomorph for the sexual one, holomorph for the whole fungus. The whole fungus was properly named after its teleomorph, because fungi are classified by their sexual organs. Even if hardly anyone had seen that stage.

My favorite example is Botrytis cinerea. Persoon named it in 1794, and the name means something like “clusters, like ash”: a gray fuzz on the berries. In a wet autumn this is gray rot, and the harvest is lost. But if dry weather follows the damp, the rot turns noble: the fungus draws the water out of the berry, the sugar stays, and grapes like these make Tokaji aszú and Sauternes. All of it is the asexual stage’s work. The sexual one, Botryotinia fuckeliana, is seldom seen. De Bary gave it its name, after the mycologist Karl Fuckel, and the name means nothing else. Under the 1981 rule, the correct name of the fungus that makes Sauternes was the name of the stage that isn’t in the vineyard.

Left, Botrytis cinerea: a gray grape with thin stalks rising from it, clusters of spores hanging from the tips of their branches. Right, Botryotinia fuckeliana: a black sclerotium in the soil, with three brown cups on stalks growing out of it. Between them, a dotted line and the caption “one fungus.”

In the early nineties the rule lost its footing: DNA lets you put a fungus in its place in the system without seeing any spores at all. On July 30, 2011, in Melbourne, the congress adopted “one fungus, one name,” starting January 1, 2013. David Hawksworth estimated that two to three thousand genus names and ten to twelve thousand species would have to be revisited. About seventy leading taxonomists signed a paper saying the time for it had not come. Hawksworth later remarked that the question had changed: it had been “one name, one fungus,” and now it was “one fungus, which name?”

The choice went not only by seniority but by who used which name. Trichoderma (1794) against Hypocrea (1825): the subcommission for these fungi held a poll, and Trichoderma won. The industrial fungus known as Trichoderma reesei and, in its sexual stage, Hypocrea jecorina, is now Trichoderma reesei. Botrytis stayed Botrytis. Penicillium took in Eupenicillium, so Fleming’s penicillium stayed a penicillium. It was renamed itself, for a different reason: in 2011 DNA showed that Fleming’s strain is P. rubens, though for decades it had been called P. chrysogenum. Industry, it seems, will go on calling it the old way.

The longest argument was over Aspergillus. Pitt and Taylor proposed splitting it by sexual stages, and then A. fumigatus, the cause of aspergillosis, would have become Neosartorya, and the geneticists’ favorite fungus, A. nidulans, Emericella. Samson, Houbraken and their coauthors kept Aspergillus whole and made the sexual names the names of its subgenera. It went the other way too: another branch of the penicillia, which DNA showed to be separate, left for Talaromyces, a genus with a sexual name, and the former Penicillium marneffei went with it. But more often the stage that won was the one people actually meet.

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