Finding Oxytropis nana

Image: Putative Oxytropis nana from Natrona Co., WY, observed by FrontRangeWildflowers: (© CC-BY-NC)

The Wyoming Locoweed (Oxytropis nana) is a rare species whose entire documented range is within the borders of Wyoming: (see also the 2023 Fabaceae Volume of Flora of North America).

Welsh (in FNA, 2023) describes the species as intermediate between Oxytropis sericea and O. multiceps. It also closely resembles O. lagopus. In both species (except var. conjugans of lagopus, which does not occur in Wyoming) the pods remain fully enclosed in the accrescent calyx. Welsh (2023) does not provide any diagnostic features for flowering plants which makes it very difficult to ID observations here on iNaturalist (most of which are made in the flowering stage).

Oxytropis nana herbarium specimens on SEINet:

Welsh's (2023) description: [to be added]

I have done my fair share of Oxytropis identifications on iNaturalist and have become familiar with a few species, but I am not an expert by any stretch. Oxytropis nana is completely unfamiliar to me but my hope is that the community might figure out a way to characterize this species based on photographs. I am therefore inviting everybody who is interested in Oxytropis to participate and share their insights.

As a first step I have assembled all observations that have at least one active O. nana ID. Many are sitting at genus or tribe level because they have other, conflicting IDs. I also added a couple of observations that have no nana ID but might be relevant. Some are from outside Wyoming and therefore likely misidentified, but I have included them here to give them fair consideration. When I assembled this list, I noticed that the IDs are very heterogenus (not surprising for a poorly known species). I therefore sorted them into morphological groups. The characters used for that are mentioned in my previous blog post on Oxytropis besseyi and related species:

Based on this, I was able to categorize observations with Oxytropis nana IDs into roughly five groups. My impression is that probably less than a handful are true nana, all the others resemble other species and are likely misdentified. However, it is also possible that O. nana simply can't be distinguished from other species except by fruit. In this case, I would expect that true nana are most likely found within Group I (lagopus lookalikes) and perhaps Group IV (oddball sericea-like plants with villous calyces).

Below are my groups. If you would like to participate in this review let me know what species each group represents, and let me know if I misplaced any observations. Also let me know about any observations I might have missed. Thanks in advance for your help!

True nana?

Group I (similar to lagopus):

[Note: BONAP does not mention O. nana from Teton Co.:]

Group Ib (pods only, calyx inflated, fully enclosing pod):

[Note: this should be var. lagopus]

Group Ic (pods emergent from calyx):

[Note: this should be var. atropurpurea but not clear how to distinguish them from besseyi without flowers.]

Group II (similar to besseyi):

Group IIb (pods only):

[Compare also to Group Ic (see note there). Note: BONAP does not mention besseyi from Sublette Co.:]

Group III (similar to lambertii):

Group IV (similar to sericea):

Group IVb (sericea? high elevation plants of compact growth habit, with white or yellow flowers):

Publicado el febrero 3, 2024 11:41 TARDE por matthias22 matthias22


Wow, thanks for doing all this organizational work Matthias! I will get to this project in time, it looks interesting.

Publicado por margaret_eaglecap hace 6 meses

@margaret_eaglecap You are welcome! This is a fun project. Perhaps you can take a look at the Group IV observations and let us know what you think about those. Nobody has more experience with Oxytropis sericea than you.

Publicado por matthias22 hace 5 meses

@aspidoscelis Thanks for looking this over! I will include those as well (your #2 is already listed under nana). I agree, they are all very good candidates for nana.

Publicado por matthias22 hace 5 meses

Now that I kind of think I know what I'm looking at, I'm mostly agreeing with your categories above. This is the only one you have listed above under 'true nana' that I don't think is Oxytropis nana:

And these three you have listed elsewhere, but I think they are Oxytropis nana:

Or, of the taxa I think I kind of sort of recognize, Oxytropis nana is the closest. However, it's occurring to me that the plants in northwestern Wyoming might just be a different var. of Oxytropis lagopus. They don't look like Oxytropix lagopus var. atropurpurea. However, I don't know Oxytropis lagopus var. lagopus, and a quick look at observations of it from Montana suggest that I would have difficulty distinguishing it from Oxytropis nana. So... maybe they're nana, maybe they're lagopus var. lagopus. I guess I would have to figure out how to distinguish those two.

Publicado por aspidoscelis hace 5 meses

Thanks again! This is very helpful!

With regard to this one: I have flip-flopped over this one. I agree that it also has some lambertii characteristics. What deterred me was the villous calyx (but see also this one: and even more so the inflated calyx, which looks quite unlike lambertii (see image #2). Also that the inflorescence remains subcapitate even in fruit. It is an outlier, for sure.

The other three look like lagopus from Montana, which I went through before I turned to Wyoming observations. They are indeed very challenging to separate. Have a look at a few more Montana observations for comparison.

It will take me a couple of days to digest all the feedback but I will make some updates to the blog post when I have gone through everything.

Publicado por matthias22 hace 5 meses

Hi Matthias, in looking at the Group IV observations I realize I can't be a huge help on this project, since I did the bulk of my O. sericea IDing in a regional context of cleaning up Western Canadian Oxytropis, particularly those in Alberta. But now you have Patrick's help for south of the border which is fantastic!

Publicado por margaret_eaglecap hace 5 meses

Yesterday, I reviewed Oxytropis observations from Mt. Washburn in Park Co., Yellowstone NP. They are all from high elevations (2,500-3,100 m). Welsh in FNA (2023) describes the elevation range of O. nana as 1,500-2,100 m. Therefore, I believe all these should be lagopus. They also look exactly like lagopus from neighboring Montana (where nana does not occur):
SEINet only has one herbarium record for O. nana from Park Co., which is on the east side of the Absaroka range: 44.4066 -109.3454 (

Publicado por matthias22 hace 5 meses

Thanks, @aspidoscelis! Your help with this project has been invaluable. I think O. nana has been found (and look-alikes properly assigned to their respective species)! At some point, I am going to summarize the findings in a new blog post.

Publicado por matthias22 hace 5 meses

Here is a handful of interesting observations that resemble Oxytropis nana, mostly from the Pawnee National Grassland in Colorado (i.e., outside the documented range of nana). @aspidoscelis noticed the first one - thanks! The fact that there are several that look alike seems to suggest that this might be a distinct entity, not just aberrant individuals. However, I think they could also be part of the hybrid swarm between sericea and lambertii (but they don't usually produce capitate inflorescences): (Logan Co., CO) (Scotts Bluff Co., NE) (very villous but taller than nana)
These ones maybe more like sericea x lambertii hybrids:

Publicado por matthias22 hace 5 meses

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