Aenigma, enigmas, and the progress of science

Image: an Enigma encoding/decoding machine (Greg Goebel, CC 0 via  Which, I admit, is only tangentially related to this piece, but it’s pretty cool.

I’ve celebrated many a Latin name on Scientist Sees Squirrel, sometimes for something as simple as the way it sounds, but more often for a story it tells.  But this time, I’m celebrating the loss of a Latin name.  Not because I didn’t like the lost name; I did.  But its loss – or, more precisely, its replacement by a new name – has a lot to tell us about the process of naming and the progress of science.

In 2017, Héctor Keller described the new genus Aenigma, a South American member of the Apocynaceae (the milkweed family).  The name Aenigma recognized both the plants’ unusual morphology and its uncertain placement in milkweed phylogeny.  My first reaction to the name Aenigma was a bit negative.  Why, I asked, should be choose a name drawing attention not to what we know about its bearer, but about how much we don’t know?

But the uncertainty Keller had about Aenigma isn’t anything to be embarrassed about.  It isn’t even anything unusual. Heck, I’m an entomologist, and we don’t even know – not even to the nearest order of magnitude – how many species of insects exist on Earth.  That’s right – as a field, entomology doesn’t even know the size of the job it has ahead of it.  I’m not picking on entomology, though; I’m also an ecologist, and ecology isn’t much better off.  In fact, I’m not sure I can name a field of science that is.  That’s part of the fun of science, of course: in every field, there are mysteries all around us, and surprises around every corner.

Aenigma wasn’t alone.  Among other creatures with names evoking mystery are the basal arthropod Anomalocaris and the basal velvetworm Hallucinigenia (both from the early Cambrian Burgess Shale), the red spinach Amaranthus dubius (which isn’t a spinach, but why quibble?) and the goby Cryptocentrus inexplicatus.  These namings, collectively, speak to the wonder we all feel, from time to time, when faced with the richness and diversity of the natural world.  Every biologist has, at least occasionally, picked up a lizard or an insect or a fossil or a plant and exclaimed “What the hell?”.  So, thinking of those “what the hell?” moments, I decided that Aenigma was a wonderful Latin name after all.

But the name Aenigma didn’t last.  Last year, Keller and Sigrid Liede-Schumann published a second paper in which they did two things.  First, they used DNA sequence data to place Aenigma within the milkweed family; and second, they gave it a new name.  Aenigma is no longer an enigma, and it’s no longer Aenigma but Topea instead.

You might be tempted to think the renaming was a reaction to our having solved the mystery of this peculiar plant’s phylogenetic placement*, but the Code that governs naming doesn’t allow name changes just because we’ve come up with a better name or a more descriptive one.  It’s more pedestrian than that.  The Code doesn’t allow the same name to  be used for two different genera**, and it turns out there was already an algal genus Enigma.  Had Keller been aware of Enigma, he’d have realized that Aenigma wasn’t a valid name for a new milkweed.  Unfortunately, and surprisingly, there’s no single compendium of the Latin names of organisms, so mistakes like this happen rather easily.

The replacement name, Topea, has a lovely etymology of its own.  “Topea” is a Guarani word meaning “eyelash”, and used as a generic name refers to the long trichomes (hairs) on the corolla (flower).  Guarani is the Indigenous language spoken by the majority of the population of Paraguay.  The plant’s new name, then, refers to something we do know about it, using the language of those who knew it first.

Aenigma’s replacement by Topea is an exception and an accident.  Most enigmatic names have stayed the same, even while we’ve made progress towards resolving their mysteries.   Hallucinogenia is still Hallucinogenia even now that we’ve figured out that it’s a velvetworm, not a hallucination.  But I choose to see Aenigma becoming Topea as a metaphor, and as a reminder: a reminder that what’s knowledge today was mystery yesterday, and what’s mystery today will be knowledge tomorrow.

© Stephen Heard  April 2, 2019

*^Yes, you’re right, I’m a little too proud of that alliteration.

**^This is an obvious and sensible way to reduce confusion.  However, the Code that governs namings for plants and algae is separate from the Code that governs namings of animals, so we can have the same genus name for an animal and a plant. Consider, for example, Morus, which can be a gannet or a mulberry, without too much danger of mixing up the two.



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