Introduction

In Australia, taro (Colocasia esculenta) is most often associated with Asian and Polynesian cooking or tropical gardens. However, taro is fast growing, able to spread in favourable conditions, and capable of becoming a serious weed of wetlands. It forms dense stands along watercourses and on the edge of lakes and swamps, displacing native plant species.

Taro is a perennial herb to 2m high. Numerous leaf stems sprout from the upright tuberous root stock, or corm. Large dark green velvety leaves are supported by thick succulent leaf stalks, coloured from green through red to a deep purple. Stalks are attached near the centre of the leaf base - a character that distinguishes them from other similar species in the arum family. Flowers are uncommon. They occur on a shorter stem, the spike of greenish white flowers enveloped by a long yellow leaflike bract.

Click to enlarge

A diverse species, taros fall into two main groups, upland and wetland taros.

Distribution, Biology and Spread

Distribution - where does it grow?

Taro appears to originate in India and south-east Asia. It has been cultivated for more than 6000 years and is found throughout much of the tropics and subtropics. Considered native to some parts of the Kimberley, taro is scattered throughout Northern Australia. However, it is known to have been introduced to Beagle Bay by Trappist Monks as a food source, and was possibly introduced to other areas.

Edible cultivars and garden varieties have been introduced into Australia more recently and taro is now naturalised in the Perth region and possibly elsewhere in south-west WA. First recorded as a weed at Maylands in 1982, taro is increasingly becoming a cause for concern along the waterways of the Swan and Moore River catchments. It prefers slightly acid, moist or wet soils rich in organic matter.

Some interesting taro biology:

• Prefers moist wet, acidic, organically rich soils and partial shade
• Tolerates intense sunlight, dense shade, permanent inundation
• Excessive nitrogen favours biomass production
• Dormant over winter in south-west Western Australia
• Flowers infrequent, produced in autumn, seed uncommon and of low viability
• Reproduction primarily vegetative; by cormules and stolons
• Allelopathic, can inhibit growth of other plants
• Contains calcium oxalate crystals which can deliver a mild sting or severe rash

How does it spread? Taro spreads by cormules, which grow off the side of the main corm, or slender stolons or both. The stolons are approximately 100 cm long by 1 cm thick, while the cormules are 4 - 6 cm in diameter. Edible cultivars and garden varieties have been introduced into Australia more recently and taro is now naturalised in the Perth region and possibly elsewhere in south-west WA. First recorded as a weed at Maylands in 1982, taro is increasingly becoming a cause for concern along the waterways of the Swan and Moore River catchments. It prefers slightly acid, moist or wet soils rich in organic matter.

An uprooted taro plant, showing the long stolon emerging from the tuber. Click to enlarge Taro stolons can reach over one metre, before putting down roots and sending up new shoots. Click to enlarge

Some interesting taro biology:

• Prefers moist wet, acidic, organically rich soils and partial shade
• Tolerates intense sunlight, dense shade, permanent inundation
• Excessive nitrogen favours biomass production
• Dormant over winter in south-west Western Australia
• Flowers infrequent, produced in autumn, seed uncommon and of low viability
• Reproduction primarily vegetative; by cormules and stolons
• Allelopathic, can inhibit growth of other plants
• Contains calcium oxalate crystals which can deliver a mild sting or severe rash

How does it spread?

Taro spreads by cormules, which grow off the side of the main corm, or slender stolons or both. The stolons are approximately 100 cm long by 1 cm thick, while the cormules are 4 - 6 cm in diameter.

Taro dispersal:

• Dispersal between waterbodies is primarily by deliberate or unintentional movement of vegetative fragments
• Cormules can also be carried by water downstream
• Population expansion is by stolons and cormules
  

  Taro corms are large and physical removal of extensive infestations results in a huge biomass to dispose of.

  Click to enlarge