Why?

Bidens pilosa (sensu lato) is split into B. pilosa (sensu stricto) and B. alba in Kew's Plants of the World Online, Weakley, and many other modern resources.

Bidens alba was previously lumped into Bidens pilosa on iNaturalist, and now needs to be split back out.

Unfortunately limited detailed info about their true global distributions is available due to the taxonomic mishmosh, but some rough atlasing was attempted based on POWO, GBIF obs not in iNat, Ballard 1986, and Weakley 2020. According to Weakley, in the southeastern United States, B. pilosa has only been reported from "NC (Kartesz 1999), perhaps based on confusion with B. alba; known from ballast in se. PA (Rhoads & Klein 1993)" (i.e. it is not known to occur in Florida). Ballard 1986 does have a dot for B. pilosa in California (page 11, Fig 17). That means that IDs of B. pilosa in Florida will be swapped over to B. alba automatically, but in California they'll be bumped back to genus.

In areas where their distributions overlap, identifications of B. pilosa will be bumped back to genus.

Bidens odorata Cav. is considered a synonym of B. pilosa on POWO and isn't treated as part of this taxon change - for that discussion, see this flag. That said, IDs of B. pilosa are going to be rolled back to genus in Mexico.

Key to identification

(from Weakley 2020 and Ballard 1986)
Bidens alba: Ray florets 5-8, the ligule 3-18 mm long; cypselas 0-2-awned, the awns 1-2 mm long; outer phyllaries (8-) 12 (-16)
Bidens pilosa: Ray florets absent (or if a few present, the ligule is only 2-3 mm long); cypselas 3 (-5)-awned, the awns 1-3 mm long; outer phyllaries 7-10

Help identify!

Head to this link to help reidentify observations that were previously IDed as B. pilosa but are currently at rank=genus: https://www.inaturalist.org/observations/identify?taxon_id=50204&ident_taxon_id=50203&rank=genus (1,878 observations before the taxon change was committed)

Note

For discussion, please comment on the flag and not this taxon change. Thanks! https://www.inaturalist.org/flags/362565

References

• Ballard, R. 1986. Bidens pilosa Complex (Asteraceae) in North and Central America. American Journal of Botany, 73(10), 1452. doi:10.2307/2443850
• Plants of the World Online. 2020. Bidens alba (L.) DC. Royal Botanic Gardens, Kew. Retrieved 30 September 2020.
• Plants of the World Online. 2020. Bidens pilosa L. Royal Botanic Gardens, Kew. Retrieved 30 September 2020.
• Weakley, Alan S. 2020. Flora of the Southeastern United States. University of North Carolina Herbarium, North Carolina Botanical Garden, University of North Carolina at Chapel Hill.