you are right, i should not call it a "red form", i only wanted to say that it´s very reddish in comparison to plants from other locations.
Yes, you are right, i´m growing them under artificial light (2 bulbs, T8 36Watt/840 and T8 36Watt/865). The distance to the plants is about 13 cm. I´ve not exchanged the bulbs since about 9 months, so the light should be not so good as at the beginning when i´ve exchanged them.
BTW, it´s one of Matthias plants, and i don´t think my lightening is more intensive than his lightening.
Perhaps the colouration has also something to do with the colder night temperatures the last few months, i really don´t know.
I´m also growing D. viridis ´Serra de Ponta Grossa, Campo Largo, Paraná State, Brazil´ and they are growing exactly next to each other but the plants are greenish, even the petioles are not reddish (sorry for the bad picture quality).
In my opinion there is a big difference in the colouration nethertheless they are growing next to each other.