I don't think that's pennywort. Pennywort is not round as pictured, and I see no roots as would be present with that plant. Also, pennywort leaves have indentations which make them more heart shaped. Those leaves appear to be round.
Having said that, I have no guess as to what it could be.
Sorry.
Definitely not Hydrocotyle leucocephala (Brazilian pennywort) I have a lot of this. This looks like Hydrocotyle verticillata (Whorled umbrella plant).
Max. height 6-10"
Growth rate: Med to fast
Midground, foreground
Light: bright to very bright
Temp: 68-77
Careful and continual pruning will eventually produce a densely packed spread of individual stems with variable leaf shapes.
a nice plant, I would like to find some for myself!
On plantgeek Hydrocotyle verticillata is listed as marsh pennywort. Is this the same as an umbrella plant I also have some pennywort in my tank but it doesn't look exactly like what is shown on plantgeek