Xanthium in the Northeastern US -- what I've learned so far
I set out this week to learn to differentiate the Xanthium species found in the Northeastern US. As is often the case, the job turned out to be more difficult than expected.
First, taxonomy of Xanthium is complicated and in a state of flux. For a feel of how this has played out in iNat curation decisions about taxonomy, visit the curation flag notes seen here https://www.inaturalist.org/flags/600588.
That said, the curator has set up six species, all of which are found in GBIF. Of the six, four are noted by GBIF to be found in Northeastern North America: these are X. echinatum, X. orientale, X. spinosum, and X. strumarium. These have, on iNat, 1, 178, 418, and 19645 observations, respectively.
Now, in contrast, only two of those species are listed in FNA. Those two, strumarium and spinosum, are also listed in Calflora, CONABIO, Natureserve, and Naturewatch NZ. FNA notes, "Tremendous disagreement exists as to the number of species to recognize." FNA folds echinatum into spinosum, but notes that doing so has its arguments against the approach. FNA folds orientale into strumarium.
And so, first, it is not correct to say that these four species listed in the iNat database do not occur in New England. All four aren't reflected in FNA because you have to read the species description in the book to find they are folded into other species based on a decision about how to handle the taxonomy.
So, how do we ID the species?
Go Botany's dichotomous key lets you separate strumarium from spinosum. This link provides info on separating strumarium from orientale https://alienplantsbelgium.myspecies.info/content/xanthium-strumarium I don't have enough Dutch to look at the source material. (I have "Good morning" and "Jump there" and "cheese" and "pancake")
I look forward to reading other thoughts..
Thanks,
peakaytea
