The green form of Colocasia grows to about 4 feet in the UK with leaves about 45cm x 30 (18" x 12"), and forms a small clump by the end of the season.
The Common Taro is widely grown as a food crop in many part of tropical Asia, and is mainly the rhizome that is eaten, but all parts of the plant contain toxins when raw. It has to be cooked very well before being eaten.
I bought my first rhizomes in 2004 from a Tropical Plant specialist company, and started them off with bottom heat. Then I found they were available from local supermarkets called Eddoes, priced by the Kg. These were a bit more difficult to sprout, but were readily available at an edible price... a bit like buying a bag of potatos.
The Rhizomes sprout readily given bottom heat, and can grow roots 15cm (6") long in a week, before top growth appears. Left in the heat the second leaf reaches about 30cm (1ft) tall. They like boggy ground with plenty of nutrients. Like Bananas, they are gross feeders, requireing a constant supply.
In warmer climates they are used in the filtration systems for Koi ponds as they suck out every last drop of nitrate, keeping the water clearer, so you feed your fish, and your fish feed the Colocasias :)
They can overwinter growing in a cool greenhouse, but if temps fall below around 3C (37F) they may go dormant. If this happens cut every last scrap of fleashy leaf material off, to avoid rot. If leaving planted out mulch heavily with NON moisture retentive material, and try to keep rain off, as more Colocasia are lost to damp than to cold.
Good fast growing plant, needs lashings of water, but the collar of the plant needs to have air