City's climate helps lobelia to thrive

Lobelia deckenii ssp. keniensis. Photo by Gerard O'Brien.
Lobelia deckenii ssp. keniensis. Photo by Gerard O'Brien.
Lobelias are common garden plants grown for their floriferous nature and many flamboyant colours. As with most plants, there are also some species that surprise you and which are often harder to tell what they are.

Lobelia are no exception, with a group of them often known as tree lobelias. Using the term tree might be stretching the imagination a bit, but they can form stems a metre or more above the ground. This is then often followed by large flower spikes extending the growth by up to another metre.

One such species is Lobelia deckenii ssp. keniensis, endemic to Mount Kenya in the mountains of East Africa. It is characterised by many rosettes of leaves interconnected by underground rhizomes.

Each rosette increases in size and height over many years until reaching maturity and flowering.

Water collects in the rosettes of leaves in the moist environments where it usually grows.

This water is important for its survival during cold weather, as when the water freezes it protects the growing tip of the plant from being damaged. The crescent-shaped ice cubes that form in the rosettes give this plant its common name of gin and tonic lobelia.

Surprisingly, Lobelia deckenii ssp. keniensis is surviving well in Dunedin Botanic Garden, due to the city's climate reflecting that of its native high-altitude habitat.

Lobelia gregoriana (previously known as Lobelia deckenii subsp. keniensis) and another giant African lobelia, Lobelia aberdarica can be seen in the South African Garden in the Geographic Collection at Dunedin Botanic Garden.

- Dylan Norfield is the geographic and arboretum collection curator at Dunedin Botanic Garden.