So it actually does occur here in Rio de Janeiro and I've eaten it. It is quite popular among middle class eco-gastronomers simply cooked as a vegetable to compliment rice and beans. It's maybe not as widely used traditionally as food as might be expected. it has various common names but I think the most used in these parts is picão-preto.

So referring to Kinupp & Lorenzi (2014) they list as wild edibles for Brazil from this genus:
B. pilosa / Bidens alausensis / B. leucanthema / B. pilosa var. minor (all the same species, just taxonomers can't make their minds up).

Also there is: B. bipinnata var. cynapiifolia (known as picão-preto-amazônico / carrapicho) / B. cynapafolia & B. fusca (known as jambu, this is well known as a seasoning as it makes your mouth go numb!!! They used to use it as an anesthetic for dentistry).

For B. pilosa they (Kinupp & Lorenzi 2014) give recipes for ice tea, risoto and also simply sautéeing. The nutritional qualities they list seem quite impressive, as is normal for such wild food gems!

I was thinking if it occurs in the States it's surprising that I haven't seen it in Ireland. It's one thing for a plant to occur in the tropics and subtropics and not make the temperate zone, but it seems it does quite nicely in reality in colder climes.