khaki weed

Alternanthera pungens
habit in fruit (Photo: Sheldon Navie)
creeping habit (Photo: Sheldon Navie)
leaves, hairy stems and flower clusters (Photo: Sheldon Navie)
close-up of flowers and fruit (Photo: Forest and Kim Starr, USGS)
seedling (Photo: Sheldon Navie)
comparison of small matweed (Guilleminea densa), left, and khaki weed (Alternanthera pungens), right (Photo: Sheldon Navie)
Herb
Opposite
Simple
Green
Yellow
Green

A long-lived, low-growing plant that forms a dense mat over the ground surface. Its creeping stems are somewhat hairy and produce roots at their joints. Its paired leaves usually differ in size (i.e. one leaf of the pair is significantly larger than its partner). Its greenish or greenish-yellow flowers are grouped together in small clusters (8-12 mm long) in the leaf forks. Some of the flower parts become hardened and form sharp prickles as they mature.

Common names 
Also known as: khaki weed, creeping chaffweed, khaki burr,
Family 
Amaranthaceae
Deciduous 
No
Flowering time 
Spring-Autumn
Native/Exotic 
Exotic
Origin 
Native to South America (i.e. Venezuela, Brazil, Ecuador and Peru).
Notifiable 
No
Council declaration 
Class R – Reduce populations
Known distribution 

Widely distributed throughout all the mainland states and territories of Australia, where it grows in all but the driest environments, but is predominantly found in and around towns. Particularly common and widespread in New South Wales and Queensland, and relatively widespread in the Northern Territory and in the northern and western parts of Western Australia. Also naturalised in many parts of South Australia, in northern Victoria, in the ACT and on Christmas Island.

Habitat 

This species grows in tropical, sub-tropical, semi-arid and warmer temperate environments. It is a weed of disturbed sites, bare areas, roadsides, parks, lawns, waste areas, watercourses, turfgrasses, orchards, and occasionally also native pastures and grasslands.

Habit 

A small, long-lived (i.e. perennial), creeping (i.e. prostrate), herbaceous plant with stem up to 60 cm long. This species often forms a dense mat of prickly vegetation over the ground surface.

Impact and control methods 

Khaki weed (Alternanthera pungens) is mainly regarded as a weed of lawns, pastures and disturbed sites near habitation. However, this species is also regarded as an environmental weed in large parts of northern Australia (i.e. in northern Queensland, the Northern Territory and northern Western Australia. In fact, during a recent survey, it was listed as a priority environmental weed in five Natural Resource Management regions throughout Australia.This species initially tends to be found along roadsides and in other highly disturbed sites. However, it can spread from these areas into disturbed natural environments and occasionally invades native pastures on sandy soils, where it out-competes most other species with its mat-forming habit.In Queensland, where this species is very common, there are numerous references to it being somewhat of a problem in natural areas. For example, one Queensland Parks and Wildlife publication describes khaki weed (Altrnanthera pungens) as an "introduced environmental weed species" in the desert uplands region in Queensland. Thuringowa City Council includes it amongst other weeds species in its list of potential environmental pests and it is regarded as a medium priority weed species in the Mackay-Whitsunday Wet Tropics region. Nebo Shire places it amongst a list of species that cause damage to the environment if not managed accordingly, while it is regulated by local law in the Beaudesert Shire due to its adverse impact on the environment.Khaki weed (Alternanthera pungens) is also spreading through the Northern Territory, having been recorded in the Darwin, Gulf, Katherine, Victoria River and Alice Springs districts. In Western Australia, khaki weed (Alternanthera pungens) is said to grow along creek banks, drainage channels and in grasslands and other disturbed natural vegetation.It is also widespread in New South Wales, where it has been reported from disturbed sites in conservation areas, particularly in drier inland regions (e.g. in Willandra National Park, Cocoparra National Park, Warrumbungles National Park, Mount Kaputar National Park and Narran Lake Nature Reserve). Khaki weed (Alternanthera pungens ) has also been recorded in conservation areas in South Australia (i.e. Coorong National Park) and north-western Victoria (i.e. Barkindji Biosphere Reserve).

Stem and leaves 

The creeping (i.e. prostrate) stems are produced from a tough and thickened central crown. They often have a reddish appearance and produce roots (i.e. adventitious roots) at their joints (i.e. nodes). These stems are covered with short, soft, hairs (i.e. they are pubescent). Similar hairs are sometimes also present on the leaf stalks (i.e. petioles) and leaf blades. The oppositely arranged leaves usually differ in size (i.e. one leaf of the pair is significantly larger than its partner). They are egg-shaped in outline (i.e. ovate) or oval (i.e. elliptic) in shape with margins that are entire or slightly wavy. These relatively small leaves (8-60 mm long and 6-30 mm wide) have rounded tips (i.e. obtuse apices) and are borne on very short stalks (i.e. they are sub-sessile).

Flowers and fruits 

The inconspicuous greenish-yellow or greenish-coloured flowers are grouped together in small globular clusters (8-12 mm long and 6-10 mm wide). These flower clusters are borne in the leaf forks (i.e. axils) and may become slightly elongated as they mature. Each flower has five 'petals' (i.e. perianth segments or tepals) that become whitish or straw-coloured as the fruit mature. Two of these 'petals' (i.e. perianth segments) are significantly longer than the others and develop a sharp point at the tip. Barbed hairs are also present at the base of the 'petals' and they become hardened and form prickles as the fruit reaches maturity. Flowers also have 4 or 5 stamens and an ovary topped with a tiny rounded (i.e. capitate) stigma. Flowering occurs from spring through to autumn. The tiny fruit (i.e. utricle) is about 1 mm long and has a flattened top (i.e. truncate apex). It usually remains hidden inside the old, prickly, flower parts. Seeds are tiny, yellowish or orange in colour, and shiny in appearance.

Reproduction and dispersal 

This plant reproduces mainly by seed, though stem fragments may also take root after being dislodged from a plant.The seeds are contained inside a 'burr' which readily becomes attached to animals, clothing and other objects (e.g. vehicle tyres). They may also be dispersed by water movement and in contaminated agricultural produce (e.g. fodder and pasture seed). Stem fragments can be spread by machinery, livestock or cultivation.

Similar species 

Khaki weed (Alternanthera pungens) is similar to some of the native joyweeds (e.g. Alternanthera denticulata, Alternanthera nodiflora and Alternanthera nana) and may also be confused with low-growing species that produce burrs (e.g. Soliva spp. and Acanthospermum spp.). It is also similar to gomphrena weed (Gomphrena celosioides), which is also known as "soft khaki weed", and small matweed (Guilleminea densa). Lesser joyweed (Alternanthera denticulata), common joyweed (Alternanthera nodiflora) and hairy joyweed (Alternanthera nana) may have a creeping (i.e. prostrate) habit and very similar flower clusters to khaki weed (Alternanthera pungens), but these species do not produce prickles.Bindy eyes (Soliva spp.) do produces prickles from its flower parts, however these species have very different, highly divided, leaves. Paraguay burr (Acanthospermum australe) is also very similar, but its burrs have numerous small hooks instead of sharp spines. Gomphrena weed (Gomphrena celosioides) and small matweed (Guilleminea densa) may be distinguished by their lack of prickles, and gomphrena weed (Gomphrena celosioides) also by its larger whitish flower clusters that are borne at the tips of its branches.