Also did a Google search on where it grows wild. It seems to like heat, shade and wet areas like ditches and apparently grows wild in southern US states.
http://www.herbs2000.com/herbs/herbs_gotu_kola.htm
HABITAT AND CULTIVATION
The gotu kola grows native in most of the tropics, though it is believed to be a native species of India; it also grows in the wild in the southern US states. At the same time, wild populations of the gotu kola herb are also seen growing in the tropical and subtropical parts of Australia, the Southern parts of Africa, as well as the South American tropics. The gotu kola herb tends to prefer marshy areas and riverbanks in the tropics. While it is hard to grow, the gotu kola is cultivated from seeds during the spring season, while commercially it is usually gathered from the wild. Harvesting of the aerial parts of the herb is usually carried out throughout the year in many places.
From Wikipedia:
The crop matures in three months and the whole plant, including the roots, is harvested manually.
Habitat
Centella grows along ditches and in low wet areas. In Indian and Southeast Asian centella, the plant frequently suffers from high levels of bacterial contamination, possibly from having been harvested from sewage ditches. Because the plant is aquatic, it is especially sensitive to pollutants in the water, which easily are incorporated into the plant.[2][3]
from Answers.com
http://www.answers.com/topic/gotu-kola
Gotu kola, a perennial, grows in India, Sri Lanka, Madagascar, South Africa, China, Indonesia, Australia, and North America. It can grow like a weed, but its description depends on its location. For example, in shallow water, the leaves float; but in dry areas, the plant develops many roots and thin, tiny leaves. The fan-shaped leaves may be smooth or lobed. Red flowers turn into fruit with a diameter of about 0.2 in (5 mm).
Sounds like it grows wild in Australia:
http://www.au.gardenweb.com/forums/load/ozherb/msg0123212816224.html
RE: gotu kola - Centella asiatica
Posted by daisyduckworth NSWAust (My Page) on Wed, Jan 25, 06 at 16:38
It grows best in shade or partial shade. Soil should be fairly rich and sandy, and must be kept constantly moist. It tolerates almost any kind of soil, but does best in alluvial soils, and prefers hot, humid climates. It may die in drought but return after rain.
Truth is, once you've got it, you've always got it - in superabundance! It can quickly become a weed, and can become an environmental thug. (Roots will grow from every stolon that touches the soil - and there's a stolon every 3-4cm or so along every runner!) The climate in SE QLD is perfect for it.
Hope this helps
(The streets are deserted here; everyone is watching the US-Canada Olympics hockey game!)