The Symbiotic Life of Roridula Gorganio

Roridula, an insectivorous plant genus native to South Africa, has unique features that distinguish it from other insect trapping plants.

Hikers of the Cape Fold Mountains will be familiar with the various drosera, the local insectivorous plants, found on damp slopes, like this type below in flower, deep in the Cederberg.

But there is a less common insectivorous type of fynbos knocking on the door of the endangered list, the Roridula, found in a few dwindling locations. The plant's interests lie not in the bugs it entraps, but in what comes out of one particular bug, which escaping the plant's sticky secretions, sucks the life out of those that have been caught.

Sticky resinous glands on the Roridula's leaves act as traps. However, unlike other local carnivorous plants, they do not produce digestive enzymes to break down the prey. Instead, they rely on symbiotic relationships with an insect known as the Pameridea. It feeds on trapped insects, and in return, it excretes a nutritious liquid that the Roridula then absorbs through its leaves, which supplements what it doesn't get from the notoriously nutrient-deficient Cape mountain soil.

Pameridea

This insect escapes being trapped in Roridula's sticky glandular leaves due to a waxy coating on its body that repels the sticky substance produced by the plant. This coating is thought to protect the insect from becoming stuck on the leaf surface.

Pameridea live on the Roridula plant and feed on the insects that become trapped in the sticky glands. In exchange, it secretes a sugary liquid that is absorbed by the plant. This mutually beneficial relationship is thought to have evolved over millions of years and has become a key feature of the Roridula's unique adaptation to its environment.

Evolution of the Roridula

The evolution of Roridula is still not fully understood, but it is believed that the leaves' secretion evolved as a mechanism to defend against herbivores. Over time, the plant evolved to trap insects and developed a mutually beneficial relationship with the Pameridea insect.

Genetic studies have shown that Roridula is not closely related to other carnivorous plants like the Venus flytrap or the pitcher plant. Instead, it belongs to a separate lineage of flowering plants that have convergently evolved carnivorous traits. This suggests that the evolution of carnivory in plants may have arisen independently in multiple lineages, rather than being inherited from a common ancestor.

Two different species

Roridula gorgonias and Roridula dentata are two species of the Roridula genus. While these two species share some similarities, they also have some distinct differences.

A main differences between the two is geographic distribution. Roridula gorgonias is found primarily in the southwestern Cape Province of South Africa, while Roridula dentata is found further east, in the eastern Cape Province and KwaZulu-Natal.

Another difference is in their physical characteristics. Roridula gorgonias is larger than Roridula dentata, with leaves that can grow up to 10 centimeters long. Roridula dentata, on the other hand, has smaller leaves that are usually less than 5 centimeters long. Additionally, Roridula dentata has teeth along the edges of its leaves, whereas Roridula gorgonias does not.

Another interesting difference between the two species is that while both species rely on the Pameridea bug for nutrition, studies have shown that the insects living on Roridula gorgonias are more specialized and have a greater dependence on the plant than the bugs that live on Roridula dentata.

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