Weeds of Australia - Fact Sheet

Top Scientific Name Family Common Names Origin Cultivation Naturalised Distribution Habitat Habit Distinguishing Features Stems and Leaves Flowers and Fruit Reproduction and Dispersal Environmental Impact Legislation

Scientific Name

Tropaeolum majus L.

Family

Tropaeolaceae

Common Names

garden nasturtium, Indian cress, nasturtium, tall nasturtium

Origin

This species comes from South America. However it does not grow in the wild, only being reported from cultivated and naturalised populations. It is thought to be a hybrid between Tropaeolum ferreyrae and Tropaeolum minor, both of which are native to the Andes region in western South America (i.e. Ecuador and Peru).

Cultivation

Nasturtium (Tropaeolum majus) is a widely grown garden plant (i.e. ornamental), particularly in the wetter parts of the country. Numerous cultivars are available with flowers in a wide variety of colours (yellows, oranges and reds are most common).

Naturalised Distribution

Nasturtium (Tropaeolum majus) has become widely naturalised in the coastal districts of southern and eastern Australia (i.e. in south-eastern Queensland, the coastal districts of central and northern New South Wales, southern Victoria, south-eastern South Australia and the south-western and western parts of Western Australia). Also naturalised on Lord Howe Island.

Widely naturalised overseas in southern Africa (e.g. Zimbabwe), the Canary Islands, Europe (i.e. Portugal, Hungary, the UK, Denmark and Finland), New Zealand, Hawaii and some parts of the USA (i.e. California, Virginia, Pennsylvania, New Hampshire and Massachusetts).

Habitat

A weed of watercourses (i.e. riparian vegetation), urban bushland, roadsides, railways, gardens, disturbed sites and waste areas.

Habit

A short-lived (i.e. annual or biennial) herbaceous plant with creeping (i.e. prostrate) or sprawling stems growing 0.5-2 m long.

Distinguishing Features

• a short-lived herbaceous plant with creeping or sprawling stems that are somewhat fleshy.
  
  
• its and rounded leaves (4-15 cm across) have entire or slightly lobed margins.
  
  
• these leaves are borne on long stalks that attach to the centre of their undersides.
  
  
• its showy orange, yellow or red flowers (2.5-7 cm across) have a long and narrow spur (2.5-4 cm long) at the base.
  
  
• its fleshy pale green fruit (about 10 mm long) split onto three ribbed 'seeds'.

Stems and Leaves

The stems and leaf stalks (i.e. petioles) are pale green in colour, hairless (i.e. glabrous) and somewhat fleshy (i.e. succulent).

The green or slightly bluish-green leaves are borne on stalks (i.e. petioles) 5-30 cm long that are attached to the centre of the leaf undersides (i.e. the leaves are peltate). These leaves (4-15 cm across) are rounded in shape (i.e. orbicular) with entire, wavy (i.e. undulate), or slightly lobed (i.e. sinuate) margins. The leaves are hairless (i.e. glabrous) and have several prominent veins that radiate outwards from the centre of the leaf blade.

Flowers and Fruit

The flowers are borne singly in the upper leaf forks (i.e. axils) on stalks (i.e. peduncles) 15-25 cm long. These flowers (2.5-7 cm across) have five yellow, orange or red petals (2.5-6 cm long) and five sepals (1-2 cm long) that are fused together at the base. One of these sepals is formed into a nectar-bearing spur (2.5-4 cm long) that is either straight or slightly curved. The flowers also have eight stamens and an ovary topped with a style and stigma. Flowering occurs mostly in spring, but also in summer and autumn.

The fleshy (i.e. succulent) fruit (about 10 mm long) separate into three one-seeded segments (i.e. mericarps) when mature. These 'seeds' (i.e. mericarps) are pale green in colour and prominently ribbed on one side.

Reproduction and Dispersal

This species reproduces by seed and vegetatively via pieces of its fleshy (i.e. succulent) stems.

The seeds and stem segments are probably spread by water and in dumped garden waste.

Environmental Impact

Nasturtium (Tropaeolum majus) is regarded as an environmental weed in Victoria, South Australia, New South Wales, Queensland and Western Australia.

Legislation

Not declared or considered noxious by any state government authorities.