The twin-apple tree, which is considered locally extinct in Singapore, has been planted back on the island, using saplings propagated from a mother tree that was kept in a National Parks Board (NParks) nursery for more than a decade.

Also known as Ochrosiaoppositifolia, two saplings of the species were planted in Coney Island Park yesterday at the launch of a programme which aims to introduce 50 species of coastal plants there over the next five years.

The twin-apple tree produces a fruit that looks like two green apples fused together.

Launched in partnership with OCBC Bank, the programme is part of NParks' ongoing habitat-enhancement efforts under the Nature Conservation Masterplan (NCMP).

The NCMP, announced in 2015, lays out Singapore's biodiversity conservation roadmap until 2020.

NParks said the project is one of the most diverse habitat-enhancement projects planned for Coney Island so far.

Other rare species such as the damak-damak tahun (Scolopiamacrophylla) - which was believed to be extinct until it was rediscovered in 2014 - will also be introduced to a 4ha land area.

Prior to the launch of the programme, site assessments had been carried out by NParks to document and understand the health of the habitats, and to determine suitable restoration techniques.

The plants introduced will then act as seed sources for the subsequent regeneration of the natural ecosystem.

"While we are only working on a 4ha plot of land, this can become a catalyst for the dispersal of the plants to the entire island," said NParks group director of parks Chuah Hock Seong.

Staff volunteers from OCBC will be working with NParks on different aspects of the habitat-enhancement process, from the collection and propagation of the plants, to outreach efforts such as conducting learning expeditions.

The bank management and staff also donated $250,000 to the Garden City Fund, a registered charity established by NParks, to support this programme.