Plant 398

Myrmecodia species (Rubiaceae)

Ant plant

Myrmecodia is a small genus of southeast Asian tropical forest epiphytes, where they cling to branches in the canopy and along forest margins. An adaptation that enables these plants to reach the best available light, which comes at a cost to the plant’s nutritional needs. Myrmecodia would have to rely on what could be gleaned from fallen vegetation and rainfall for their nutrients were it not for cooperation between plant and insects.

Myrmecodia belongs to a group of plants termed ant plants or myrmecophytes. This group is characterised by symbiotic and mutualistic relationships with ants that have evolved over millions of years. Ants are key components of many ecosystems. Tropical forests are no exception. From the forest floor to the canopy, myriad species of ants perform roles such as pollination, seed distribution, protection and organic waste recycling.

Relationships that exist between a colony of arboreal ants and Myrmecodia are beneficial to both. Ants and the plants would survive without each other, but both increase their ability to thrive through mutually beneficial cooperation.

Myrmecodia species develop a swollen and tuberous, succulent stem called a caudex. Within these stems is a labyrinth of cavities, termed domatia, creating a protected environment in which ant colonies live. The domatia are often interconnected, enabling ants to move within the stem between the various hollows. Access is via an opening in the caudex with the ants moving freely between the cavities and the forest. Ants use the domatia as nurseries for raising their broods. As the organic waste that accumulates as part of colony life breaks down, it provides nutrients for the plant. Occasionally reptiles are found co-habiting with ants inside the domatia of large, mature plants.

Some Myrmecodia species have nectaries, sunken within the stem, that provide food, in the form of sugary nectar, for the ants. The discreet location of the nectaries gives these ants exclusive access to a valuable food source.

Myrmecophytes, such as Myrmecodia, have been a focus of research for the University of Oxford’s Department of Plant Sciences and Botanic Garden. For example, in the 1970s and 1980s, Camilla Huxley focused her research on the scientific descriptions of the morphology and ant-associations of all five of the myrmecophyte genera in the Rubiaceae. Myrmecodia is one of several grown at the Botanic Garden, where germination protocols and horticultural growth trials help us to determine optimum ex situ conditions for propagation and cultivation.

Chomicki G 2020. Ant plants: epiphytic Rubiaceae. In: Starr C. (ed) Encyclopaedia of social insects. Springer, Cham.

Chomicki G and Renner S 2015. Phylogenetics and molecular clocks reveal the repeated evolution of ant-plants after the late Miocene in Africa and the early Miocene in Australasia and the Neotropics. New Phytologist 207: 411-424.

Huxley CR 1978. The ant plants Myrmecodia and Hydnophytum (Rubiaceae), and the relationships between their morphology, ant occupants, physiology and ecology. New Phytologist 80: 231-268.

Kate Pritchard