My final upload for 2024 is Nostoc. It’s nice to end the year with a cyanobacterium – my third bacterial observation and third bacterial taxon. The times I have gone through the “Unknown” iconic taxon (as opposed to “true unknowns”), I noticed that Nostoc is disproportionately observed and often left at the genus level. I just did some checking, and here is what I found:
15,051 total observations of Nostoc spp.
12,211 observations of Star Jelly (Nostoc commune).
2,706 observations of Nostoc only at the genus level.
769 observations of all 15 other Nostoc species combined, including 351 of the second most-observed species, Mare’s Eggs (Nostoc pruniforme), and 5 species with one observation each.
So, just as I had thought, we have more observations stuck at the genus level than all runner-up species combined. Assuming that these are not ALL N. commune, taking them to the species level would help to fill in the diversity of this genus. As many of the species-level observations are at Research Grade without miscroscopy, this suggests that colony morphology can be used as an identifying trait.
I wouldn’t mind trying my hand at this, if I can find suitable reference materials; but if someone is going to come along behind me and knock them all back to genus again, I will feel like, “why did I bother?” What says the community about this?
Not to deter turn-of-year enthusiasm, but https://link.springer.com/chapter/10.1007/0-306-46855-7_17 (2002) contains the extremely depressing sentence “Despite the fact that Nostoc spp., collectively, represent a unique biological resource, there is no adequate species concept for the group; the origins of Nostoc and other heterocystous cyanobacteria are unclear; and the physiological and molecular traits which could provide diagnostic features of a Nostoc remain elusive”. Well, that was before the molecular era really got underway.
Or it suggests that people aren’t aware of other possibilities with that general morphology (no local observations of any other species on iNat; general nature guides only mention Nostoc commune, etc.) and so people agree to that ID because it is distinctive so it must be right.
It is also quite possible that people are following a pragmatic morphology-based identification principle that may or may not correspond with whatever the current scientific consensus is about how this genus should be classified.
(I don’t know anything about Nostoc taxonomy specifically; it may be that many people follow a “form species” concept because no other viable species concept is currently available and one can ID based on morphology with a clear conscience – my point was that “there are lots of RG observations on iNat” is a shaky basis for drawing conclusions about whether there are lookalike species. If it is a taxon where there is not a lot of easily available information, iNat is susceptible to circular reasoning where people make assumptions based on existing observations and each subsequent observation reinforces the belief that there is only one species that needs to be considered.)