For many gardeners, the first image that Lobelia brings forth will be of a mass of royal blue flowers on the scrambling Lobelia erinus, frequently used as a bedding plant in the summer. Although used as an annual filler, this species is a perennial originating from southern Africa. The scarlet flowers of Lobelia cardinalis and Lobelia tupa can also be found in many herbaceous borders. These species both originate from the New, rather than the Old, World.
The genus was named for Matthias de L’Obel (1538-1616), a Flemish physician and botanist. After studying in Montpellier, he lived and worked across Europe, before settling in England where he became personal physician and ‘Botanist Royal’ to King James I. He is remembered as the first botanist to appreciate the difference between monocotyledons and dicotyledons.
The genus Lobelia currently includes 439 accepted species, although ongoing investigations into the familial relationships of the genus will bring alterations in the future.
This fascinating groups of plants have a remarkable story of migration and diversification to tell. Data show the genus Lobelia to have originated in southern Africa before undergoing a dramatic cosmopolitan diversification approximately 20 million years ago. Species found their ways to Madagascar and eastern Asia, the Mediterranean, North America, South America and Australia. The details of these multiple colonisation events are still being unpicked using genetic analyses of relevant species, although not all information may be recovered due to the extinction of some lineages. The original Lobelioid ancestor that arrived 13 million years ago on the Hawaiian Islands has since given rise to over 125 extant taxa of incredible variety – a spectacular example of adaptive radiation.
Diversity of growth forms and ecological niches amongst the lobelias is also impressive: from the small herbaceous form of Lobelia erinus to the statuesque two-metre-tall flowering spikes of Lobelia tupa in late summer and from the aquatic Lobelia dortmanna to pachycaul giants, such as Lobelia gibberoa growing in the mountains of East Africa, with their short, fat trunks.
Diversity continues at a chemical level. Piperidine alkaloids, exemplified by lobeline, are the most significant group of metabolites specific to Lobelia. These biologically active molecules lead to myriad uses in traditional medicine. Examples include the use of Lobelia gibberoa in Ethiopia against gastrointestinal problems, and Lobelia inflata in North America to treat respiratory diseases. In early nineteenth century North America, Lobelia siphilitica was promoted as a cure for syphilis.
Folquitto DG et al. 2019. Biological activity, phytochemistry and traditional uses of genus Lobelia (Campanulaceae): A systematic review. Fitoterapia 134: 23-38.
Givnish TJ et al. 2009. Origin, adaptive radiation and diversification of the Hawaiian lobeliads (Asterales: Campanulaceae). Proceedings of the Royal Society B: Biological Sciences 276: 407-416.
Knox EB and Li C 2017. The East Asian origin of the giant lobelias. American Journal of Botany 104: 924-938.