They watched over Singapore long before its independence from the British, and some even date from the 19th century.
Now, some of the Civic District's trees - such as the angsana and rain tree - are to get greater recognition as part of a 3km-long Civic District Tree Trail to be launched by the National Parks Board (NParks) on May 1.
It will include monthly guided walks and markers at all 20 stops along the route, which starts at the entrance of the Istana and ends at the Raffles' Landing Site.
Among the highlights of the trail is an avenue of 22 heritage rain trees in Connaught Drive which was unveiled in a ceremony officiated by Senior Minister of State for Home Affairs and National Development Desmond Lee yesterday, in conjunction with Car-Free Sunday.
It is the largest number of trees in a single avenue to be endorsed under NParks' heritage tree scheme, which identifies important green landmarks.
More than 250 trees have been selected since the scheme was launched in 2001. They were evaluated by a panel that includes NParks staff and landscape experts, based on criteria such as their rarity, size, health and social, cultural or historical significance.
Some of the heritage rain trees in Connaught Drive date back to the mid-1880s and have witnessed key events in the district, including Singapore's declaration of independence from the British by then Prime Minister Lee Kuan Yew in 1963, and Singapore's first National Day celebrations in 1966.
Epiphytes such as ferns and orchids tend to grow on old rain trees.
Ms Kalthom Abdul Latiff, deputy director of arts and heritage parks, said the trail will allow the public to learn about natural heritage in the heart of Singapore.
"We are all familiar with the historic buildings," she said.
"Now, we also want to showcase our natural heritage. Members of the public walk under the trees every day... We want them to appreciate the greenery around them."
Mr Desmond Lee added: "Even as we continue to plant new trees, we must also cherish and protect the trees that have been maturing gracefully since Singapore's early days."
Other stops along the trail include one at the National Museum, where an old Indian rubber tree that can be traced back to 1955 still stands today.
NParks has developed other tree trails for various parks and green sites. These include heritage tree trails such as the Changi Walking Trail.