Alien plants on the increase:

Lanka, a repository of endemic flowers

By Dhaneshi YATAWARA

Cannonball flowers (Sal)

Flowers; they are with us throughout our life - in joy and in grief. We choose them to express our feelings and flowers have neither complained nor shown their joy over our decisions. Be it on the Mal Asana of a temple or among the garbage, flowers are beautiful to the human eye wherever they may be. A bouquet of flowers would always heal the sick and a grieving heart.

A place with brightly coloured flowers, beautiful trees and abundant greenery is a paradise, for us. And undoubtedly, Sri Lanka is a paradise.

The island nation holds the record of the world’s highest rate of endemism in the world of flowers. Sri Lanka's fauna and flora have the world's highest rate of endemism with 16 percent of its fauna and nearly 30 percent of its flowering plants being endemic to the country.

According to statistics, on an average, a little over 17 endemic plants can be found in a 100 square kilometre area in the Western Ghats and Sri Lanka.

Flowers contain the reproductive parts of a flowering plant, scientifically known as ‘Angiosperms’. Since plants cannot move from place to place, many elaborate methods are devised by nature that helps identify a plant.

“It is because certain characteristics - such as the number of petals, the number of stamens, the arrangement of petals and the shape of bunches - are constant for a particular type of plant that botanists primarily use flower characteristics in identifying plants,” according to the book ‘Flowering Plants - commonly encountered in Sri Lankan habitats’ written by Dr. Sriyani Miththapala, Dr. Siril Wijesundara and Dr. Janaki Galappatti.

Flowering plants

Sophora violacea is found only in the Royal Botanical Gardens in Peradeniya and is believed to be already extinct in the wild. The flower has not been reportedly observed in the wild in the recent past. Pic: Sudam Gunasinghe

Orchids and above Binara flower

Botanists categorise this repository of flowering plants into different segments. Dr. Siril Wijesundara, Director General of the Department of Botanical Gardens said, “Flowering plants can be seen in four categories. Native and Endemic plants are two of the four types which we have heard of often and know exactly what they mean. The other two categories would be Naturalised and Alien plants. Alien plants are species, subspecies or lower taxa introduced outside of their natural range (past or present) and outside their natural dispersal potential.” Naturalised plants, as Dr Wijesundara explained, are alien plant species that reproduce and sustain populations without direct intervention by humans, often producing plentiful offspring.

These are alien plants that sustain self-replacing populations for at least 10 years without direct intervention by people through seeds, tillers, tubers, bulbs or plant fragments which are capable of independent growth.

In Sri Lanka, the number of alien plants is increasing and there are nearly 200 naturalised plants identified by botanists. Fortunately or not, many of the beautiful flowering plants we have in our surroundings are introduced species, according to Dr Wijesundara. Among the invasive plants we find in Sri Lanka, 37 species were introduced more than a 100 years ago. Another 14 species were introduced between the past 100 and 50 years and seven had been introduced during the past 50 years.

Habitats being destroyed

As the three authors explain in the book ‘Flowering plants’, alien plants that can replace native plants and destroy habitats are spreading at a dangerous pace. Farmers plant exotic crops and horticulturists transplant ornamental species. In Sri Lanka, Mesquite (Prosopis juliflora) and Prickly Pear (Opuntia speices) have spread in the Bundala National Park, replacing its native vegetation, while ‘Lantana’ is doing the same at the Udawalawe National Park, according to the book.

Water lilies

Wrightia antidysenterica, Wal ldda which is endemic to Sri Lanka is also used as an ornamental plant

Every time a person brings in an untreated plant to this country, it could be facilitating the spread of invasive plants.

According to Dr. Wijesundara, there are nearly 1,000 endemic flowering plants in Sri Lanka that are recorded and identified. The island is home to 18 endemic plant genera. The flowering plants of Sri Lanka belong to 1,369 genera and 3,771 species.

As a direct consequence of human activities, the possiblity of species facing extinction is now 1,000 times greater than the accepted norms, the authors explain in the book, referring to global data.

Accordingly, in 2009, the International Union for Conservation of Nature (IUCN) listed 10,876 flowering plants as threatened with extinction as a result of various human activities. Sri Lankan flowering plants numbering 675 have been listed here as threatened.