Just to add to the knowledge...

On
Petra Mees' aquarium site (in German, she also keeps a LFS in Berlin), the following information is given:
'Vesuvius' is a mutation of
Helanthium angustifolium (
Echinodorus angustifolius) made in the Oriental Aquarium (S) Pte Ltd, in Singapore.
It will grow upto ca. 45 cm.
She grows it in the following conditions (a translation):
"Temperature 25-27 degrees C,
Tapwater with 8 kH / 18 dgH, pH 7,6.
Tank height 50cm, lit with 2 x 30 Watt Osram Daylight "Lumilux 11" and reflectors, on for 12 hours daily.
Liquid fertilisation is given at weekly water changes, occasional addition of root tabs as well."
There are 2 pics:
Emersed motherplant
Flower
(which show undeniably that it is a
Helanthium.)