POWO does not focus on subspecies. The fact that there are no subspecies on POWO does not mean that there are no subspecies!
DO NOT SINK THIS SUBSPECIES.

Yes: that is standard taxonomic procedure in the literature - it implies that the subspecies are included in the species - but not necessarily that they are sunk, but it might be incorrectly transferred in POWO. I dont know well enough: I would prefer to the see primary literature where it was "sunk" before sinking it.

If that is the case, then there are subspecies currently missing because I. p. brasiliensis is the only subspecies listed under Ipomoea pes-caprae.

Hi @alexiz This is a subject of interest for me, and the taxon change affects a species that is part of sandy beach systems that I study, so I am keen to be on top of the latest information. I'm an ecologist and not a taxonomist, so I'm here to learn. Please can you explain why subspecies brasiliensis was dropped?

I had a look for the most recent research on Ipomoea pes-caprae, and found this:
Wood JRI, Muñoz-Rodríguez P, Williams BRM, Scotland RW (2020) A foundation monograph of Ipomoea (Convolvulaceae) in the New World. PhytoKeys 143: 1–823. https://doi.org/10.3897/phytokeys.143.32821
"Ipomoea pes-caprae is commonly divided into two subspecies or varieties. Only subsp. brasiliensis (or var. emarginata, if recognised at varietal level) occurs in the New World. It is recognised by its emarginate leaves, whereas the type from the northern Indian Ocean area has deeply bilobed leaves, the lobes somewhat divergent. Opinions about the status of these two forms have varied over the years. Recent molecular studies (Miryeganeh et al. 2014) suggest the two forms are genetically separate and rarely hybridise but some intermediates occur and the issue is not yet fully resolved."

(Link to Miryeganeh et al. 2014 in my previous comment in this thread)

Perhaps this subspecies should be retained until, as @tonyrebelo suggested, there is primary published research indicating that these subspecies are not valid? Especially because it seems that the recent genetic evidence is in support of the subspecies, even if - as Wood et al (2020) point out - it's not yet fully resolved. I'm just wondering what the motivation was for removing this subspecies (and still keeping ssp. pes-caprae). Thanks very much - appreciate your time.

EDIT: I completely misunderstood the situation. I thought I had committed this taxon swap prematurely. I now see that that is not the case.

If I recall, part of my reservations was that Kew had started to reinstate subspecific taxa for many plants on POWO, but continued to treat Ipomoea pes-caprae brasiliensis as a synonym (not a child taxon) of Ipomoea pes-caprae. My intention was to contact Kew to ask them why and share what they told me here, but life unfortunately got in the way and I forgot to do so. While I still think it's a good idea to contact Kew - and to share the information you all provided - there is no issue with reinstate the subspecies at least in the interim.

Unfortunately, they probably amount to 3000 of the 3300 observations.
Any chance of requesting a rollback?