Unknown plant

I am positive that the plant you are describing is Ludwigia arcuata.  I have
actually ordered a dozen of them from Mike and he has yet to deliver.  They
are very fine leaved plants that grow yellow and red.  The leaves grow
opposite, thn and long.  See page 99 of the Baench Aquarium Atlas for more

Kh2-12, pH6.0-7.2, T:64-75...the nice thing about it is that is a good
self-propagator.  You need good water with iron rich fertilizer to maintain
the red color.