Tomb, sarcophagus, ant

Unlike the traps and tricks used by pitcher plants (Nepenthes), bladderworts or sundews (see Carnivorous to learn more), which largely take advantage of animals by consuming them to compensate for depauperate soil nutrients, the plants we see here have more insidious methods. Think the Rotenburg Cannibal.

Formally known as myrmecophytes but invariably referred to as ‘ant plants’, the plants herein have a special kind of mutualistic association with whole ant colonies. A mutualistic association means that both the plant and the colony of ants benefit from the arrangement.

So why the grim title to this article? What’s the deal?

One word: domatia.

Domatia are internal plant structures that are specially adapted to house ants. Cute, right? Oh DO read on…

Botanical name: Dischidia rafflesiana

Family: Asclepiadaceae

A slender climbing vine, D. rafflesiana’s ‘normal’ leaves are small (<1 cm), fleshy disks that range from cream through light yellow into green. At intervals, however, the plant produces clusters of something more interesting – specially-modified ‘ant leaves’.

These ant leaves form wrinkly yellow/orange cups that are hollow inside; a fine and cosy home for their resident ant tenants. To maximise rent from it’s occupants, D. rafflesiana grows a mass of fine roots into each hollow cup. When hoarding ten-ants drag in debris or pass through deaths door, the specialised fine roots inside the ant leaf absorb the nutrients made available as they decay.

Botanical name: Hydnophytum formicarium

Family: Rubiaceae

H. formicarium is the plant with the grossly distended root base. It looks a little like the outside of a wooden brain. Inside it, sinuous passageways provide a spacious home for resident ants.

Botanical name: Phymatodes sinuosa

Family: Polypodiaceae

This fern is easily spied thanks to its horny, snake-like tubers – can you spot them? Spotted oblong leaves spring skyward from the tubers. The rows of orange circles mark the underside of the leaf. They are called ‘sori’ (a singular ‘sorus’ or many sori), clusters of sporangium, which produce and release the reproductive spores from the plant.

As in D. rafflesiana‘s cup-shaped ant leaves, the additional nutrient supply provided by debris and decaying ants inside the tubers of H. formicarium and P. sinuosa confers a competitive advantage in the harsh conditions of kerangas forest.

It is also likely that the resident ants provide some protection for their host plant against lurking herbivores, like soldiers defending the barracks where they eat, sleep and live. 

The ant plant habit or behaviour has developed across diverse clades – over 100 different genera – from Australian Acacia trees to ferns in the Asian tropics. This is likely because of the ubiquity of ants – estimated by some to be the most ecologically dominant animals in tropical rainforests, potentially comprising as much as 94% of the arthropods (e.g. insects) that live in the forest canopy. 

So what do you think? For one, I find it hard to feel warm and fuzzy about the domatia of these Bornean myrmecophytes.  

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