El Gran Ficus

This tree keeps adding trunks. El Gran Ficus drops aerial roots from its branches, and the ones that reach the ground thicken, stiffen and set as columns, so what began as a single Moreton Bay fig is now a colonnade about 30 metres high that visitors walk into rather than around. It is the youngest tree on this list by centuries. The garden's Swiss head gardener Hermann Wildpret, in post from 1860 to 1893, planted it in the 1870s, which makes it roughly 150 years old; one guide puts it at about 200 without naming a planting date, and the documented planting is the better bet. The garden itself is far older, founded by royal order of Carlos III in 1788 and inaugurated in 1792 to acclimatise tropical plants to a European climate, so the fig is a latecomer to its own address by a century. Sources disagree on the fine print of what it is, some naming the Lord Howe Island form of the species rather than the mainland Australian one; nobody has settled it, and if you know, tell us. The garden is compact, about two hectares, and charges a few euros, but this is not a specimen you have to hunt for once you are through the gate.