This is a follow up thread to this one: Curious About Shepherd’s Purse. In that thread, @blue_celery agreed with me that other species besides Capsella bursa-pastoris are likely to have spread outside their native range. Now, in the current iNaturalist dataset, we find, as expected, C. bursa-pastoris observations worldwide:
When we check C. rubella, we see that it is almost entirely confined to Europe, with a couple of interesting exceptions:
When I was first doing this investigation, the outlier in Iceland – research grade – was the furthest from the native range. The one in Kansas was added just two weeks ago, and the one in California, four days ago. Neither is yet at research grade.
One of the links that @blue_celery provided was documentation of C. rubella occurring cryptically in Chile – a datapoint that does not exist on iNaturalist, although there are many observations of C. bursa-pastoris in Chile. My hypothesis is that C. rubella is more widespread in North America than the two observations suggest; some may even be misidentified on iNat as C. bursa-pastoris due to “field guide bias,” i.e. the field guides only say that bursa-pastoris is present, so that is what users assume every Capsella they see is.
The other link from @blue_celery has this handy illustration of the seed capsules:
Now, I have some shepherd’s purse that I have been growing out from seed, and now that it has capsules, I am certain that it is rubella. You can see its capsules here:
Note that the lobes have concave sides, and flare outward, in keeping with the above illustration for rubella. Now, I do not feel that I can post this as an observation, since it is captive/cultivated, and the location and date are inaccurate. But suppose I return to the original collection locality at the appropriate time of year, and post an observation of the parent plants? My concern is, if I ID it as Capsella rubella, will that get a fair consideration by the community, or will it automatically be reassigned to C. bursa-pastoris “because the literature says so”? I am aware that my being certain has no scientific standing; so how would I demonstrate it?
I also wonder: if I went through the North American observations of “Capsella bursa-pastoris,” carefully examining them to see if any are really rubella, how much would the community support me?