Alien invasion

Be cautious of what you grow in your garden...

By Dhaneshi YATAWARA

The Valentine plant

Did you know that those gorgeous plants which decorate your garden may harm the environment at some point if released to the wild?

According to researchers, many of the plants that upset the natural balance of the environment were those introduced to Sri Lanka as ornamental plants, e.g. Water hyacinth.

According to research done by Director General of the Department of Botanical Gardens Dr. Siril Wijesundara, nine plant species commonly used as ornamental plants have the potential of becoming invasive plants - if grown irresponsibly. Today these plants can be seen growing in natural eco-systems after having escaped their gardens.

Namely, the Indian cork tree, Parrot feather, Stream bog moss, Glory bush, Mosaic plant, Donkey grass or Creeping guinea grass, Bristly foxtail grass, Valentine plant and Arabian wax cissus are the nine plants that are thriving in the environment. Research has revealed alarming facts about these ornamental plants.

Such troublesome plants mostly arrive in the country through humans and the majority are brought here as ornamental plants. Having no sense of the would-be impact on the environment, people would just throw these plants away once they start growing too fast. In next to no time they grow rapidly over a vast area, outside the gardens, from where they were dumped, and become invasive in the natural eco-system.

Arabian wax cissus

Botanists call them Invasive Alien Species as these plants are alien to the eco-system, having being introduced from a totally different environment. Today Invasive Alien Species (IAS) have become a global menace. These plant species, when introduced in a new location, spread outside their natural habitats, causing deleterious effects on organisms that already exist there. Most of these invasive plant species colonise in areas with high levels of human disturbance, but many have also been apparently invading undisturbed eco-systems, and threatening many of the endangered indigenous species and habitats with extinction.

Water hyacinth (Eichhornia crassipes) Japan Jabara is one of the best examples of an ornamental plant which became a menace to aquatic eco-systems.

This aquatic plant species was introduced to Sri Lanka in 1905, to the Royal Botanical Gardens, Peradeniya. Lady Edith Blake, wife of the 10th British Governor of Sri Lanka Sir Henry Arthur Blake brought this aquatic plant to Sri Lanka from Hong Kong as an ornamental plant. It was first planted in the Peradeniya Gardens. Sir Blake, before being posted to Sri Lanka, was the Governor in Hong Kong from 1898 to 1903. He governed Sri Lanka from 1903 to 1907.

As Dr. Wijesundara explained, quoting historical records, by June 1912 Water hyacinths had been reported from Wattegama in the Central Province. In 1914 it had appeared near Tangalle in the Southern Province and two years later, in Chilaw in the North Western Province. By 1917 it was found in the Sabaragamuwa Province.

Lantana

"As a means of controlling this aquatic plant, four ordinances were enacted in 1930. They were the Water Hyacinth Ordinance No. 4 of 1909, Plant Protection Ordinance No. 10 of 1924, Village Communities Ordinance No. 9 of 1914 and Irrigation Ordinance No. 45 of 1917," said Dr.Wijesundara quoting earlier research details.

Possible threats

One of the commonest ornamental plants growing in the wild is the Valentine plant (Clerodendrum quadriloculare). Native to the Philippines, this ornamental plant is grown in many parts of Sri Lanka and blooms in February, hence its name. As a result of careless growing by gardening lovers the plant is fast spreading in the wild. It is considered an invasive plant of the highest priority on the Hawaiian Islands.

The Indian cork tree (Millingtonia hortensis), belonging to the Bignoniaceae family, is a plant native to South East Asia. It flourishes in the dry zone and is seen mostly in degraded sites in Embilipitiya and Thanamalwila areas.

Aquatic plant

Another aquatic plant called Parrot feather (Myriophyllum aquaticum) grows well in the montane zone. This is a native aquatic plant of the Amazon river in South America.

Ulex - an invasive gorse in the Horton Plains

According to Sri Lankan researchers, this has been reported growing out of home gardens in the Gregory's Lake in Nuwara Eliya. This is seen as an invasive plant in many countries including USA, Pacific Islands, Japan, New Zealand, South Africa and several European countries.

Mayaca fluviatilis, commonly known as Stream bog moss is also an aquatic plant. It has been reported from water bodies in the vicinity of Gampaha and is believed to have been thrown away or escaped from home gardens. Mosaic plant (Ludwigia sedoides) is another aquatic ornamental plant which has escaped in to the wild, and is mostly seen in the vicinity of Gampaha. The plant is ideal for the wet zone.

Glory bush (Tibouchina urvilleana) is another ornamental plant which people should carefully grow. One can find a glory bush thicket near the Anderson bungalow in Horton Plains. Glory bush is native to Southern Brazil and is reported to be invasive in Hawaii and some Pacific Islands.

Donkey grass or Creeping guinea grass (Panicum trichocladum), a native grass from Africa imported as a pasture grass, is found to be spreading in Hanguranketha, Pelmadulla and Kadawatha areas. Bristly foxtail grass (Setaria barbata) is another grass native to Africa which is now spreading in the wet zone. Another invasive plant would be the Arabian wax cissus (Cissus rotundifolia) native to Africa.

According to the study, 31 plant species are found to have already invaded our eco-systems, causing havoc. Cuscuta, Lantana, Mimosa, Opuntia and Salvinia are some of those invasive plants that have become a menace.

Invading nature

According to Dr. Wijesundara's study, these invasive plants could be in the form of herbs, shrubs, creepers or trees. They may invade terrestrial or aquatic eco-systems. Some of these species such as Cuscuta are parasitic. According to available data, most of these invasive alien plants reported from Sri Lanka are vascular plants.

Water hyacinth

Ludwigia

Alien plant species could be deliberately introduced when they are useful, interesting or ornamental, and also imported through standard institutions.

"Some plants, which have been deliberately introduced for a specific purpose, have escaped from their compounds and become invasive," Dr. Wijesundara said.

As he explained, Salvinia was introduced to Sri Lanka in the late 1930s as educational material, but appears to have escaped and is currently one of the most troublesome aquatic invasive plants, blocking irrigation canals and water bodies and also invading aquatic eco-systems.

The other example, the giant mimosa (Mimosa pigra) is believed to have been introduced to Sri Lanka in the early 1980s to strengthen the river banks in the Mahaweli areas. Today it has spread to other parts of the country by irrigation water, machinery, river sand used for construction purposes as well as through lopped off branches with mature pods as a result of the use of the stems of the plant as firewood by people.

Such plants need to be treated with special care and propagated by artificial aid. When a plant becomes independent of artificial aid of any kind, and thrives in the wild after escaping its cultivation, it can develop in to an invasive level.

"Invasion can be considered as an integral part of the evolution process and deliberate plant introductions date back to the early days of human civilisation," said Dr. Wijesundara, explaining that even the origin of some of the most useful crops grown all over the world are still unknown.

"When growing plants brought from other countries, people must first understand the impact their characteristics will have on our nature. If it is negative it is very important to grow these plants ensuring that they will not be dumped carelessly," Dr. Wijesundara said.

Thus, it is vital to be careful and responsible when growing these wonderful plants in your garden as a plant that looks lovely may not actually fit into our eco-system; worse, it could harm and destroy the existing environment.