01-02-2012, 01:49 PM
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I can't be "positive" as requested
but I would offer the suggestion that this is Ludwigia arcuata
. Another marsh plant, the emersed leaf is green but submersed leaves are green to red; high light intensity enhances the red colouration. Kasselmann writes that the submersed leaves will become green with insufficient lighting, as you appear to be noticing. As we've been discussing in your other thread, light intensity is crucial with red leaf plants since water absorbs red wavelengths rapidly.