Curious about shepherd's purse

[jasonhernandez74]

The Wikipedia page on Capsella has a list of 27 species, of which only a few appear in blue indicating that they have their own pages. When I hover my mouse over the blue ones, I find that the tooltip indicates most of them as synonyms of Capsella bursa-pastoris. The only exceptions are C. gracilis, C. grandiflora, C. orientalis, and C. rubella. Based on what I have read elsewhere, I assume that the ones in red are also synonyms.

So here are my questions: This source implied that the weedy, exotic populations around the world are all C. bursa-pastoris. However, my 1980 edition of Peterson’s Field Guide to Wildflowers: Northeastern/Northcentral North America has both C. bursa-pastoris and C. rubella as occurring “throughout,” distinguished by the shape of the silique. Which is correct? Is this a case as has been discussed in other threads re: dandelions, i.e. all weedy specimens are assumed to be one species when it is not so? Or is C. bursa-pastoris indeed the only widespread weedy one? How would one determine this?

[blue_celery]

27? I thought they were 270, at least…
Just a joke but they are surely less than 27, possibly even less than those listed in POWO.
Here the authors analyze 5 species considered at that time the representatives of the genus:
https://www.biotaxa.org/mjbs/article/viewFile/26571/24565

I do not have a crystal ball, anyway I would say that, unless new findings will suggest to adopt a broader concept of Capsella, we will remain well under 10 species.

@jasonhernandez74

Or is C. bursa-pastoris indeed the only widespread weedy one? How would one determine this?

I think that it is almost impossible that C. rubella has not spread out its area of origin.

@jasonhernandez74

How would one determine this?

1 - Annuals or biennals. Petals well exceeding sepals. Lateral sides of the silique flat or convex: C. bursa-pastoris
1 - Annuals. Petals slightly exceeding sepals at most. Lateral sides of the silique concave: C. rubella

Distinction is often made difficult by the presence of apparently intermediate plants.

References:
https://www.publish.csiro.au/BT/BT14135
https://orbi.uliege.be/bitstream/2268/174415/1/1978%20Bull%20Soc%20Roy%20Bot%20Belg%20111.pdf