Thinking about Gumweed
Went down a bit of a rabbit-hole this morning trying to reconcile some confusion I have regarding the taxonomy of local Grindelia sp. I want to document here the chronology of my confusion and hopefully end up with a greater understanding of what species should be expected in my locale and how they should be identified.
My confusion began when I queried the USDA Plants website to determine what species of Grindelia occurred in Laramie county. I was somewhat relieved to see that only two species were reported, and one had the common name "Subalpine gumweed" leading me to believe that the only species I was likely to encounter in the vicinity of Cheyenne, WY was Grindelia squarrosa .
I was interested to learn that there were two varieties of Grindelia squarrosa : quasiperennis and serrulata. I naturally wanted to know how to distinguish the two varieties.
The first resource I found describing the distinction between these varieties was here, which reported the following:
"There are currently three varieties recognized in Missouri: var. nuda, which lacks ray florets, var. quasiperennis, which has entire or inconspicuously toothed leaf margins, and var. squarrosa, which conforms to the descriptions above and the most common in this state. The taxononmy [sic] of the complex is still not fully understood."
No confusion yet, var. quassiperennis must have entire or very-reduced serrations on the leaf margins and var. serrulate, as indicated by the scientific name, as well as the above quote, will have obvious serrations.
Next I reviewed all the Grindelia observations to see if I could put this information into practice and identify which specimens were serrulate and which were quasiperennis. Nearly all appeared to be the former, and I reported the ones I were reasonably confident about as Grindelia squarrosa var. serrulata. However, there were one or two that had nearly entire leaf margins and I wanted to classify them as Grindelia squarrosa var. quasiperennis.
This is where things became confusing.
When typing Grindelia squarrosa var. quasiperennis into iNaturalist I was instead prompted to classify the specimen as Grindelia hirsutula. I know from personal experience that this meant that Grindelia squarrosa var. quasiperennis was a synonym and Grindelia hirsutula was the accepted name. However, Grindelia hirsutula was not listed in the Plants USDA website and they also claim to only report accepted scientific names. Moreover, Grindelia hirsutula was reported to be in Oregon and California according to the original sources cited in the relevant Wikipedia article, so Grindelia hirsutula would, apparently, be out-of-range here.
Some clarity to this confusion came when I read the efloras.org species description of Grindelia hirsutula. Firstly, it seems that the Plants USDA website is in the wrong here (and iNaturalist was correct) since Grindelia squarrosa var. quasiperennis was listed as a synonym for Grindelia hirsutula. Secondly, we can see that Grindelia hirsutula has a much broader range than was reported by any of the Wikipedia sources. Thirdly, we can see that what would originally be reported as Grindelia squarrosa var. quasiperennis is one facies of Grindelia hirsutula. To make sure the third point communicated clearly, I am including the relevant efloras quotation below.
"As circumscribed here, Grindelia hirsutula includes 30 or more reputedly distinct, local, regional, or ecotypic facies that have been named at species or infraspecific rank. Locally, such facies are easily recognized; in a broad view, they intergrade with other facies and are parts of a heterogeneous continuum. Taxonomies that have attempted to recognize the facies as distinct "taxa" have led to almost as many specimens determined as "intermediate" as are assigned to the named "taxa.""
Therefore, it appears that there are three species of gumweed in Laramie Co: Grindelia hirsutula, Grindelia squarrosa, and Grindelia subalpina. In a later post, I will try to explain clearly how they should be distinguished, but until then if any of you have any insights or resources on how to best distinguish these species in Laramie Co. I would welcome you to comment here.
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