Giant mimosa/Giant sensitive Tree (Mimosa pigra)

An introduced  shrub native to the Mexico, Central and South America. First identified at the Mahaweli river bank near Kandy in 1996 (But probably colonized there since early 1980's.). It is now considered as a invasive plant and widely distributed along flood plains of some rivers and along roads when sand from the river bed has been used for road constructions. 

Mistflower/Spreading snakeroot (Ageratina riparia [Syn: Eupatorium riparium])

Native herb of Mexico and West Indies. Probably introduced as an ornamental (Earliest specimen was collected from the neighborhood of  Hakgala Botanic garden in 1926). Escaped and widely naturalized along roadsides and tracks, margins of cultivation and forest edges and waste lands above 1300 m elevations.It has become a serious weed and listed as a invasive plant to Sri Lanka. Mistflower forms a dense strand and prevent the growth of native plants. Seeds spread by wind and water. Flowering from December to May and probably throughout the year.

Mission Grass/Crab Grass (Setaria parviflora [Syn: Pennisetum polystachion])

Native plant of tropical Africa. Introduced to Sri Lanka as an ornamental grass. Escaped and naturalized along roadsides, cultivated lands, fallow fields, etc. from sea level to about 1100 m a.s.l. It has become an invasive weed of forests and plantations. 

වෙල් ආතා [Wel Atha]/Pond Apple/Alligator Apple/Monkey Apple (Annona glabra)

An invasive tree spreading aggressively in southwestern wet lowland marshy areas, mangroves, near paddy fields, forest edges, etc. Common near the coast.  Native tree of tropical and sub tropical coastal areas of the America and west Africa. 

ඉලුක්[Illuk]/Blady Grass/Spear Grass/Cogon Grass (Imperata cylindrica)

An introduced perennial weed grows in coastal areas, sand dunes, open places, roadsides, waste lands,  agricultural fields, ditch banks, etc. from sea level to about 1200 m asl. It is ranked as one of the 10 worst invasive weeds of the world. Spear Grass usually flowering after stress such as drought, burning and cutting. The seeds disperse by the wind and remain viable for over one year. 

Carrot grass/Carrot weed (Parthenium hysterophorus)

Native herb of tropical America. Probably introduced into Sri Lanka in 1988 since it was first observed at the School of Agriculture at Vavuniya which Indian Peace Keeping Force occupied at that time. Now a widely spreading invasive weed of abandoned fields, waste lands, roadsides and cultivated grounds. The plant is toxic and can cause skin and respiratory system problems.

These plant were observed at a roadside location close to the Mathale town (7°27.769'N, 80°37.767'E)

ගහල[Gahala]/Taro/Elephant's ear (Colocasia esculenta)

An introduced large herb probably with Southeast Asian origin. Now pan-tropically cultivated and also escaped and naturalized in open wet places. Very common from lowlands to intermediate altitude throughout the country. Its underground stem edible and many edible and ornamental cultivars exist. It is considered as an invasive since dense stand of wild Taro displace native flora and block waterways, canals and invade rice fields in the wet zone. 

හුලන් තලා [Hulan tala]/Goat weed/White weed (Ageratum conyzoides)

Native herb of tropical America. Very common invasive weed along roadsides, cultivated grounds and waste places throughout the island. Flowering throughout the year. Flowers white, blue or mauve.

Phyllanthus pulcher

Small shrub native to tropical Southeast Asia. Introduced and now an invasive in disturbed rain forest habitats of Kalutara and Ratnapura districts.

Devil's ivy/Pothos/Money plant (Epipremnum aureum)

An introduced ornamental  climber native to the Solomon islands. Cultivated and also escaped and naturalized in the lowlands to hill country forests. Rarely flowering.

කිඹුල්වැන්න[Kibulwenna]/Alligator weed (Alternanthera philoxeroides)

Native herb of Brazil and Argentina. Invasive in Australia, China, New Zealand,Thailand and USA. In 1995 it was found that Alligator weed has been growing in home gardens of  the Sri Lankan community in Australia as a vegetable by mistake*.  Later on somehow it was introduced to the Sri Lanka and now an invasive weed in several areas, growing in dense masses in shallow water.

* Invasive Plants - A guide to the identification of the most invasive plants in Sri Lanka, Lalith Gunasekara

Siam weed/Devil weed/Common floss flower (Chromolaena odorata [Eupatorium odoratum])

An introduced large herb native to tropical South America. It was first introduced an ornamental at Peradeniya botanical garden in 1884 where it subsequently dead out. When it was next introduced is not recorded but during 1937-1947 it became naturalized in Balangoda  Ratnapura area and spread rapidly up to extend that it was considered as a dangerous weed in 1944. It is now listed as an invasive which is very common along roadsides, waste grounds and forest clearings at lower elevations. Flowering from January to July. 

යෝධ බෝවිටියා[Yodha Bowitiya]Cancer vert/Purple plague,Velvet tree/Bush current(Miconia calvescens)

Small tree introduced as an ornamental plant due to its large attractive leaves. Native to central and south America from Mexico to Argentina. Now become naturalized in disturbed forest areas of montane zone. Listed as an invasive plant to the country. Common in Ginigathhena area. 

Gorse/Furze/Whin (Ulex europaeus)

An introduced spiny shrub naturalized in forest edges, along roadsides and other open areas of montane zone. Native plant of western Europe.

වතු පාලු/ගම් පාලු/ලෝක පාලු/කෙහෙල් පාලු/මහ කිහිඹිය/Vatu-Palu/Kehel-Palu/Gam-Palu/Loka-Palu/Maha-Kihimbiya/Mile-a-minute (Mikania cordata)

An introduced (Native? >>) and very common creeping and climbing herb often growing over and covering other plants and shrubs. It is a weed of forest edges, roadsides, waste lands and secondary forests. Flowering from October to March. Native to tropical Asia, Philippines and New Guinea. 

ඉපිල් ඉපිල්/Ipil Ipil/ Wild Tamarind/Cofee bush (Leucaena leucocephala)

An introduced shrub or small tree cultivated as green manure, fodder, for afforestation and as cover plants of tea estates. It is native to the tropical America. Since it has the ability of rapidly spreading to adjacent areas and invade all other native flora, Ipil Ipil is now considered as an invasive.

කටු පතොක්/Katu Pathok (Opuntia dillenii)

Native to the South America. Introduced as an ornamental plant and now naturalized common weed in sandy places of dry and arid zone especially in Bundala and Yala national parks.  Fruit edible.

ජපන් ජබර [Japan Jabara]/Water hyacinth (Pontederia crassipes [Syn: Eichhornia crassipes])

A floating herb native to Brasil and other South American countries, which introduced and naturalized in tropical African and Asian countries including Sri Lanka. It was introduced to Sri Lanka in 1905 as an ornamental plant and now a common invasive plant in most water bodies such as tanks, canals, ponds etc of lowland dry and intermediate parts of the island . Propagated mainly by runners (stolons) which produced new plants.

Kosters curse/Soap bush (Miconia crenata [Syn: Clidemia hirta])

An invasive shrub native to the South America. Introduced probably as an ornamental plant and naturalized in several tropical countries including Sri Lanka. It is widely distributed along rain forest pathways and streams of wet and montane zones. Also in roadsides and disturbed grounds of lowland wet zone to tea estates in up country. Propagation is mainly due to the seeds spread by birds. 

දියපර/ගොඩපර[Diyapara/Godapara](Dillenia suffruticosa)

Native plant of Sumatra, Malaysia and Borneo. Introduced to Peradeniya botanical garden as an ornamental tree in late nineteenth century. It becomes an invasive plant in stream banks, forest edges, wastelands, roadsides and neglected plantations of wet lowlands. A bright yellow flower of this species is the key to distinguish it from other three indigenous varieties of Dillenia (with white flowers) grows in Sri Lanka.