Thanks, JDowns, L. Glandulosa is probably right ... I thought I looked at all of the ludwigia varieties, but I missed this one.

Thanks for the links, ceg... The 2nd link even had a pic of P. Stellata -- Broad Leaf (first time I've been able to find a pic of it), which is not all that different from my plant, though I still lean toward L. Glandulosa.