The confusing tick-trefoils
Desmodium glabellum (tall tick-trefoil) and Desmodium perplexum (perplexed tick-trefoil) are members of the Desmodium paniculatum complex. The specific name perplexum suggests these taxa are confusing, which is indeed true. Until recently, it was very difficult to distinguish Desmodium glabellum from Desmodium perplexum. In 2020, a breakthrough research result put these species on the map (both figuratively and literally). For more info:
- The confusing tick-trefoils (googledoc)
The googledoc includes an identification key, references, and links. A short glossary is also included.
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Thank you for this summary. Nicely done!
Thanks @tsn I hope to see more of these species in the summer!
Good job on this one! It could be more useful if you could expand the range beyond New England.
Thanks @chuckt2007 in Missouri, almost 60% of the herbarium specimens were found to be incorrectly identified. [Thomas 2020]. In Pennsylvania, Desmodium glabellum was found to be considerably more common than Desmodium perplexum, which was an unexpected result. [Weakley et al. 2022; page 401] cc: @rachgo
In the googledoc, I chose to summarize the iNat observations in New England since that's close to home, and since I knew those observations had been recently reviewed. I don't know the status of observations in other regions. @ciafre @vvoelker have the observations in other states or regions been reviewed? TIA
I'd heartily agree it would be preferrable for iNat to diverge if POWO accepts FNA, although I'm hoping POWO can be persuaded otherwise. A large number of southeastern US states follow FSUS, which follows Thomas's very coherent treatment for the paniculatum complex, it would be frustrating for those of us in the region in to see these species reduced to vars on iNat. Ohashi's 2013 treatment also reduces the ciliare complex to a single polymorphic species comprised of three vars, D. marilandicum var. marilandicum, var. ciliare, and var. lancifolium (=obtusum), another change that I (and I think most folks familiar with the trio) find hard to swallow, and FSUS has not opted to adopt this one either.
At this time @ciafre and I have worked through the New England states, NJ, NY, PA, DE, MD, DC, WV, and are currently looking through VA. We're trying to work systematically and are reviewing all Desmodium observations state by state, in regional chunks. I think we'll be moving in a midwesterly direction from VA. Things get more complex and diverse in the south, so we thought it might be best to sort out northern regions first, where the Desmo situation is a little simpler.
@trscavo Your summary of the situation is really great! We're also currently working on making identification guides to help others identify the species (either in the field or on iNat) and collect better observations. We're posting them to our newly made project (link below), and making a guide for this complex is very high on our list. When we do, would you mind if we add a link to your google doc (with credit, of course)? You've also given me the idea to periodically post updates on our progress as we complete states/regions!
Here's a link to the project: https://www.inaturalist.org/projects/desmodium-hylodesmum-of-the-us-and-canada
I should also add that Ontario and Quebec still need to be completed- lots of D. canadense observations to sort through there.
Also, right now a lot of observations we've identified are stuck at the genus or complex level, and we haven't figured out a way to pull our specific identifications to map them out by species we've identified them to. If you or anyone has ideas on how to get that info from the API, that would be great!
@vvoelker thanks for the update. Ohashi (2013) does not reduce the ranks of Desmodium glabellum or Desmodium perplexum, he simply lumps them into Desmodium paniculatum. Are other names given in FNA (2023)? I have not seen the latter.
@ciafre of course you can link to the googledoc. I've joined your project as well.
@ciafre here's a tip. Let's start with all observations of Desmodium glabellum in New England. As of this moment, there are 41 observations in that set. In the previous URL, replace the parameter
&taxon_id=130994with&ident_taxon_id=130994. Now there are 61 observations.Is this what you're looking for?
@trscavo That's close to what I want, but I was hoping to find only observations that I identified as D. glabellum. Adding &ident_user_id=ciafre narrows that down, but that url also includes observations that someone else has identified as D. glabellum (regardless of whether I agreed with the ID). To phrase it another way, the url doesn't treat ident_user and ident_taxon as mutually exclusive.
@trscavo Also, regarding your question about Ohashi's FNA treatment, here's the names he lists for the two varieties of D. paniculatum he treats (my friend sent me photos of his copy):
D. paniculatum var. paniculatum; D. dichromum, D. dillenii, D. glabellum, D. paniculatum var. angustifolium, D. paniculatum var. dillenii, D. paniculatum var. epetiolatum, D. perplexum, D. pubens, and then other names in the genera Hedysarum and Meibomia.
D. paniculatum var. fernaldii; D. fernaldii
He writes: "Desmodium paniculatum is allied with D. fernaldii, D. glabellum, and D. perplexum, and the four are called the D. paniculatum Group, which is characterized by having straight loments with 3-5 angled segments. These species have been studied intensively by B. G. Schubert (1950, 1950b,) and D. Isely (1953, 1983b, 1990, 1998). According to Isely (1990, 1998), D. paniculatum intergrades with both D. perplexum and D. glabellum, resulting in a continuum of varations among the members of the D. paniculatum Group that suggests introgression, including: D. paniculatum x D. perplexum; D. paniculatum x D. glabellum, and D. glabellum x D. perplexum. They are treated here as varieties of a single polymorphic species. The varieties are distinguished by somewhat continuous or overlapping characters."
@ciafre here are two ways to get a list of observations that you identified as Desmodium glabellum:
https://www.inaturalist.org/identifications?user_id=ciafre&taxon_id=130994
https://jumear.github.io/stirfry/iNatAPIv1_identifications.html?&rank=species¤t=true&user_id=ciafre&taxon_id=130994
The latter has tons of parameter options.
Wow, I didn't know such a tool existed- thanks so much for finding it! This should work well. The end goal would be to make maps of what we had ID'd as glabellum or perplexum- I have a feeling that it will take awhile for the community taxon of all the observations to catch up.
@chuckt2007 here are two iNat distribution maps as requested: 1) Desmodium taxa map, and 2) Desmodium compare map
Hope this helps
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