purple joyweed

Alternanthera brasiliana
habit prior to flowering (Photo: Sheldon Navie)
habit in flower (Photo: Sheldon Navie)
younger leaves (Photo: Sheldon Navie)
greenish-coloured leaves on a plant growing in a shady area (Photo: Sheldon Navie)
dark purplish leaves on a plant growing in a sunny area (Photo: Sheldon Navie)
close-up of stem and whitish flower clusters (Photo: Sheldon Navie)
seedling and young plant (Photo: Sheldon Navie)
Herb
Opposite
Simple
White
Purple

A long-lived herbaceous plant or small shrub usually growing 0.5-2 m tall. Its reddish or purplish stems are finely hairy when young, but become hairless as they mature. Its paired leaves (1-10 cm long and 0.7-5 cm wide) are usually purple-tinged or bright reddish-purple in colour. Its tiny whitish flowers are arranged in dense clusters (7-20 mm long) in the upper leaf forks or at the tips of the branches. These clusters are rounded to slightly elongated in shape and are borne on stalks usually 3-10 cm long. Its tiny brown fruit (1.5-2 mm long) contains a single seed and usually remains hidden within the old flower parts.

Common names 
Also known as: alternanthera, purple joyweed, Brazilian joyweed, calico plant, joy weed, purple joy weed, joy weed,
Family 
Amaranthaceae
Deciduous 
No
Flowering time 
Year Round
Native/Exotic 
Exotic
Origin 
Native to southern Mexico, Central America (i.e. Belize, Guatemala and Nicaragua), the Caribbean and tropical South America (i.e. French Guiana, Guyana, Surinam, Venezuela, Brazil, Colombia, Ecuador and eastern Peru).
Notifiable 
No
Council declaration 
SIL – Special Investigation List
Known distribution 

Purple joyweed (Alternanthera brasiliana) is becoming widely naturalised in the coastal districts of northern and eastern Australia. It is relatively common in northern Queensland and the northern parts of the Northern Territory. Also naturalised in the coastal districts of central and southern Queensland and in the Kimberley region in northern Western Australia. Naturalised overseas in south-eastern USA (i.e. Florida), South Africa and on some Pascific islands (e.g. Hawaii, Niue and Palau).

Habitat 

A weed of roadsides, disturbed sites, waste areas, footpaths, lawns, mown areas, riparian vegetation, open woodlands and forest margins.

Habit 

A long-lived (i.e. perennial) herbaceous plant or small shrub (i.e. sub-shrub) usually growing 0.5-2 m tall, but occasionally climbing over other vegetation and reaching up to 4 m in height.

Impact and control methods 
Stem and leaves 

"The reddish or purplish stems are finely hairy when young (i.e. villous), but become hairless (i.e. glabrate) as they mature. These stems may be upright (i.e. erect or ascending) to spreading (i.e. decumbent) in nature.
The paired leaves are stalkless (i.e. sessile) or borne on short stalks (i.e. petioles) up to 13 mm long. These leaves (1-10 cm long and 0.7-5 cm wide) are oval (i.e. elliptic) to egg-shaped in outline (i.e. ovate) with entire margins and pointed tips (i.e. acuminate or acute apices). They are usually purple-tinged or bright reddish-purple in colour and are either hairless (i.e. glabrous) or finely hairy (i.e. villous)."

Flowers and fruits 

"The small whitish flowers are arranged very dense clusters in the upper leaf forks or at the tips of the branches (i.e. in axillary or terminal spikes or racemes). These clusters (7-20 mm long) are rounded (i.e. globose) to slightly elongated in shape (i.e. cylindrical) and are borne on stalks (i.e. peduncles) usually 3-10 cm long. Each of the tiny flowers is stalkless (i.e. sessile) or borne on a short stalk (i.e. pedicel) up to 2 mm long. They have five whitish or greenish-white sepals (i.e. tepals or perianth segments) 3-5 mm long that are hairy and have pointed tips (i.e. acuminate apices). They do not have any petals, but are subtended by three small bracts (3-5 mm long). Each flower also has five yellow stamens and an ovary topped with a very short style and stigma.

The tiny fruit (i.e. utricle) is oval (i.e. ellipsoid) in shape and 1.5-2 mm long. This fruit turns brown in colour as it matures and does not open (i.e. it is indehiscent). It contains a single seed and usually remains hidden within the old flower parts. The oblong to egg-shaped (i.e. ovoid) seeds are about 1.4 mm long."

Reproduction and dispersal 

"This species reproduces by seed and also vegetatively via the rooting of stems and stem segments.

Plants can spread laterally through the rooting of stems that come into contact with the soil. Stem segments and seeds may also be spread by water, mowers, and in dumped garden waste."

Replacement species 
Alternanthera denticulata (lesser Joyweed)