Rotala verticillaris? Nope!

For those of you who aren't as edumacated like me

Rotala rotundifolia flower:


Pogostemon erectum flower (the plant formerly know as Rotala verticillaris):

If you look closely at the flowers of the Pogostemon, you'll notice that the filaments of the stamens have trichomes (hairs). No species in the entire Lythraceae family has that feature (that was what I meant to say above). Additionally, the flowers of real R. verticillaris are quite small and are right up against the stem at the nodes, totally unlike the flowers shown previously.

I noticed too, that the Japanese site Grassy Aqua lists it as "Rotala cf. verticillaris" (cf meaning similar to) and gives the place of collection as in the state of Maharashtra, in Western peninsular India (P. erectum is endemic to this area), where R. verticillaris does not grow (it does grow in the Southeastern side of the peninsula and in Sri Lanka). Not conclusive by itself, but certainly interesting.

In this case, I was fortunate to have not only a good description (Aquatic and Wetland Plants of India by C.D.K. Cook), but also well-preserved actual specimens to which I could compare my flowering material. Very neat stuff.