Alternanthera philoxeroides (Mart.) Griseb.

Code

ALRPH

Growth form

Broadleaf

Biological cycle

Vivacious

Habitat

Humid lowlands.

China: Althenanthera philoxeroides flowers from May to October.

 Alternanthera phyloxeroides is a vivacious species. It mainly spreads vegetatively by fragmentation of portions of stems which easily root at the nodes. However, sexual reproduction by seed exists only in the native area of this species (South America).

Dispersal of Alternanthera phyloxeroides is vegetative and primarily hydrochorous or by vehicles and work tools that may transfer portions of stems from one site to another.

Alternanthera philoxeroides can be confused with a. sessilis, the latter species is distinguished by its globular white inflorescences but with sessile spikes and small in size.

Brazil: Althernanthera philoxeroides can occur in all regions and grows on very wet soils or shallow water bodies, whether the water is fresh or brackish. It tolerates large temperature fluctuations and grows best at high temperatures. Light frosts destroy the leaves, while heavy frosts also destroy the aerial stems.
China: Althernanthera philoxeroides is an exotic species that grows in very wet or flooded situations such as rice fields and in rubbish tips.
Comoros: absent
Madagascar: absent
Mauritius: Althernanthera philoxeroides is a naturalized and well-established alien species, especially around the Alma area. It prefers wet conditions and is very common in irrigation canals or in the vicinity of ponds and reservoirs.
Mayotte: absent.
Reunion: absent.
Seychelles: absent.
Thailand: Althernanthera philoxeroides is an exotic species. It is an amphibious plant, which grows in rice fields and canals or on marshy soils.
West Indies: Althernanthera philoxeroides is found at the edge of coastal pools and swamps.

Voluntary introduction:

- Aquarium pathway: water from aquariums where this plant has been used may contain seeds or plant fragments (which may resume growth in the wild).
- Horticultural pathway: In Australia, people coming from Sri Lanka
cultivate Alternanthera philoxeroides by mistake (to consume the leaves) because they confuse it with A. sessilis, very popular in Sri Lanka.

Unintentional introduction:

- Water discharged from ship ballast tanks: It is likely that the plant arrived this way in 1946 in Australia.
- Transport of contaminated plant mulch: This is one of the reasons for its current expansion in Australia.

Viable forms of transport of the plant: seeds, whole plant or by stem fragments (cuttings), rhizomes (for the terrestrial form)

Environments at risk in Reunion :

Aquatic environments (fresh to brackish water): Ravines, lakes, ponds, rivers and their banks, irrigation channels...etc. Wet to swampy terrestrial environments. A. philoxeroides withstanding cold temperatures and even frost could invade the wetlands grazed at altitude. A. philoxeroides is invasive in temperate as well as in tropical zones. All this climatic gradient exists in Reunion Island. There is an aquatic form and a terrestrial form of the plant which favors its development in a wide range in a wide range of environments. Its power of vegetative multiplication by means of vegetative fragments makes this plant particularly invasive and difficult to control. A. philoxeroides is insensitive to most herbicides. The only factor limiting the development of this plant is the lack of water, which is not the case anywhere in Reunion except maybe on the littoral zone of the west coast.

Global harmfulness

- Alternanthera phyloxeroides causes the invasion of rivers and other bodies of water leading to the disappearance of local aquatic flora and fauna through competition and light interception, creating a habitat favorable to the development of mosquitoes and preventing the practice of aquatic sports or leisure.
- Clogging of canals affecting irrigation systems and fish farming.
- The ability of the plant to absorb heavy metals is a problem for countries that use it as food (Myanmar, Sri Lanka...)
- A. philoxeroides is also a weed for submerged crops such as rice and wet grazed meadows.

Huge expenses have been spent to control A. philoxeroides in many countries. In New Zealand and Thailand, biological control using a beetle (Agasicles hygrophila) has been successful. This control method does not seem to be as effective in Australia because it only impacts the aquatic form of A. phileroides and mainly in warm climate. The economic losses caused by an infestation in the irrigated area of Murrumbidgee (Australia) have been estimated at 250 million dollars per year if no control measures are taken. To date, the costs of controlling this infestation alone have been evaluated to more than 3 million dollars.

Local harmfulness

Brazil: Alternanthera phyloxeroides is an important weed in irrigated rice production. It also causes a nuisance by obstructing irrigation canals.
Mauritius: Alternanthera phyloxeroides is a weed of sugarcane with a high noxiousness because of its very rapid growth. It forms dense stands thus severely competing against the young stems of cane or vegetable crops.
Reunion Island: Absent
Seychelles: Absent 
West Indies: Alternanthera phyloxeroides is an uncommon weed in the West Indies. It is mentioned in banana plantations in the region of Capesterre in Guadeloupe.

Local control

Mauritius: Alternanthera phyloxeroides is very sensitive to mixtures of post-emergence herbicides used in the cultivation of sugar cane. It must be removed manually in vegetable crops.

Herbarium pictures ReCOLNAT: https://explore.recolnat.org/search/botanique/simplequery=Alternanthera%2520philoxeroides