The small flower size immediately tells me it’s not section Taraxacum. Fortunately it’s in British Columbia so we can try the key on it. Unfortunately we don’t even know what sections occur in other states or provinces, and there’s no key for all the sections in Europe, so that’s a significant obstacle for the rest of North America.
The BC key is linked here or in the paper here. I should note that this observation is from July, so it won’t be the spring leaves. Apparently later “generations” of leaves are more variable and consequently less reliable, which is frustrating… Worth a shot anyway though to see where we get.
1: It’s at a low latitude in BC but in the Rocky Mountains so it could be a high elevation. From the map/background it looks like it’s growing in a gravelly area near a road (disturbed habitat). We can’t see the bracts, but the leaves have many lobes, with a couple complex lobes. So probably non-native. 1b → 2
2: Again we can’t see the bracts, but the gravel and leaves look dry… Also if you look at representatives of sect. Palustria the flower and especially leaf shape is very different. 2b → 3
3: Stuck here because we can’t see the bracts. Always get a photo of the back of flowers of Asteraceae! (and the underside of mushrooms! :P)
However step 4 is quick, we can check out the 2 sections there. The key descriptions aren’t useful since they only discuss the seeds, but we can look at the descriptions and images of those sections later in the paper. They both seem to be small dandelions with complex leaves, which matches the one in the observation. However the T. fulvicarpum group is exclusively coastal, which eliminates it. Let’s put a bookmark on sect. Erythrosperma and try the rest of the key.
5: Issue with the bracts again here, but I think details about the leaf shape, leaf colouration, and range eliminate the sections in steps 6 and 7.
8: We can’t see the bracts but given the tiny size of the flower I’m sure the bracts are also small. The leaves aren’t large enough to be “crisped”/rugose (indented where the veins are). 8b → 9
9: The petioles (leaf stems) have no wings (thin area of leaf beside the stem). The capitula (entire flower-head of an aster) is small. The leaves aren’t egg-shaped or lance-shaped, but then neither are the leaves of the example sect. Borea in figure 1… At least it is not sect. Boreigena.
So after all that I would say that the dandelion in the observation is probably not native, and it’s probably either section Erythrosperma or Borea, leaning slightly towards the former due to the leaf shape. Let me know if you disagree with my logic anywhere there… We could have more confidence with photos of the back of the flower (to show the bracts and the stripes on the underside of the petals), and having spring leaves and knowing the shape and colour of the seeds wouldn’t hurt either.
If I had more confidence about the section I might try cross-checking the 6 sect. Erythrosperma species that Bjork lists with European identification resources, to see if they’re different enough that I might be able to decide between them and if this observation is a good match for one of them.
Another potential complication is that this plant could be smaller and have fewer leaves because it’s stressed for one reason or another. I think that’s the case with this one I found growing on a rock. It’s hard to tell without more context and other examples of similar plants in the area.
I have a couple observations of dandelions that I don’t think are sect. Taraxacum, but have had similar challenges to this with identifying them to section. It’s especially challenging without having someone more experienced to confer with most of the time.
At least you can often tell when plants are sect. Taraxacum (larger plants with large flower heads, strongly recurved bracts, complex lobed leaves with rugose centres and 3D edges, usually with pollen on the stigmas). After that you can try to get lower with the British key (sect. Ruderalia = sect. Taraxacum), with the caveat that there are definitely species in North America from elsewhere in Europe as well.