Asystasia gangetica [as Asystasia gangetica subsp. micrantha] is a form of Chinese Violet. It is initially a shrubby spindly herb of about 1 m in height. With time it may well form mats of vegetation since all of the nodes are capable of forming roots on contact with the soil; the fall of any stems will result in new plants. Flowers are tubular, white with purple markings on the lower inside surface. Fruits are up to 3 cm long, initially green, but brown when ripe. These fruits split in half explosively (drying out is probably the trigger for this) and fling out the 4 seeds. The hooks which support the seeds in the fruit are visible in the opened fruit halves (CRC 2003, PIER 2006).
For further information and assistance with identification of this form of Chinese Violet (Asystasia gangetica) contact the herbarium in your state or territory. It is confusable with other Asystasia species and there is one native species on the tip of Cape York Peninsula.
Two subspecies, A. gangetica subsp. gangetica and A. gangetica subsp. micrantha are sometimes recognised in this species in Australia. They are presently only split on flower size which is not always reliable (Barker 2007, pers. comm.), and are not treated separately here.
Asystasia gangetica [as A. gangetica subsp. micrantha] has shown a tolerance to a range of subtropical and tropical climates, and could be suited to a large part of Australia's environment (CRC 2003).
|Key points:|| |
- Apparently confined to New South Wales at this time, but with the potential to spread in tropical areas.
- A known aggressive weed from Malaysia.
- Easily spread by human activity.
- Not necessarily separable from the other subspecies which is widely grown in the tropics.
- Has been confused with a native species in the past.
|How it spreads:|
Dispersal is by explosive fruits flinging the seeds some distance, but also by the ease with which it roots at any node which contacts soil. Since it forms mats of vegetation there is always the potential for fallen stems to root and spread the plant further. Agricultural, gardening, mining and roadwork activity all have the potential to spread this species, whether by seed or plant fragments. The dumping of garden waste is thought
to have caused most of the outbreaks in New South Wales, although it has also spread at a great rate from garden plantings (CRC 2003).
|Where it grows:|
A. gangetica [as A. gangetica subsp. micrantha] grows in tropical and subtropical areas. Most of the infestations are small and occur on vacant residential land, along fencelines and in neglected garden beds. Several larger outbreaks are present along roadsides and on crown land (CRC 2003).
In all these cases the plant is found on coastal sandy soils but it is thought to tolerate a wide range of soil types. It prefers full sun or part shade. Plants in deep shade do not thrive and become spindly, awaiting a break in the canopy. Often, plants in more exposed sites show some yellowing of the leaves, especially during winter (CRC 2003).
|Flower colour:||White |
A. gangetica [as A. gangetica subsp. micrantha] is one of seventeen sleeper weeds identified by the Bureau of Rural Sciences (following consultation with the Australian Weeds Committee) which could have nationally significant impacts on agriculture if allowed to spread.
A. gangetica [as A. gangetica subsp. micrantha] is a known troublesome weed in tropical crops such as coffee, oil-palm and rubber plantations. It competes effectively for soil nutrients, reducing productivity and increasing management costs. It could also become and agricultural weed in Australia. It could potentially affect crops such as soybeans, vegetables, cut flowers and oil-tea tree (CRC 2003).
It can smother all vegetation in the herbaceous layer (Pier 2006) reducing the availability of habitat for native plants and animals, hence reducing biodiversity (CRC 2003).
In a paper on variation within the species A. gangetica, Ensermu (1994) recognised two subspecies, one the large-flowered type of the species from India, through-out Asia to Indonesia and Pacific Islands and the other a smaller-flowered African taxon, subsp. micrantha. Based on his work most Australian material would agree more closely with A. gangetica subsp. gangetica in having flowers more than 25 mm long. However material collected in New South Wales represents the more aggressive form of this species, subsp. micrantha, which has a flower length of less than 25 mm, although flower size is not always reliable in Australian material (Barker 2007, pers. comm.).
A. gangetica [as A. gangetica subsp. micrantha] was first recorded as naturalised from the Anna Bay and Boat Harbour areas near Nelson Bay, just north of Newcastle in New South Wales in 1999 (CRC 2003, Barker 2007, pers. comm.).