The Trees Of Ranau

The image shows a Terrestrial redwood. In the lower gravity of Unan Besar, the ten thousand year old Trees of Ranau (scroll down) grow much bigger:

"The slim higher boughs would each have made a Terran oak; the lowest were forests in themselves..."
-Poul Anderson, "The Plague of Masters" IN Anderson, Sir Dominic Flandry: The Last Knight Of Terra (Riverdale, NY, 2012), pp. 1-147 AT p. 121.

The huge branches can support their own weight because their cores are nearly as strong as steel whereas most of their thickness is as light as balsa, protected by hard gray bark. Bright, mirror-like upper leaves reflect light down to lower foliage which otherwise would be fatally enshadowed. The planet has only one grove of these Trees because they are succumbing to faster evolving parasites. The Ranauans preserve their grove by living in symbiosis with it.