Welcome to the Ant House

Look up in the trees in far north Queensland and you might see a living ant house – a Buddha-like plant, clinging to the upper branches of a paperbark tree.

There are only a few leaves, the flower is tiny, but the swollen belly is a give away. That’s where the ants live.

Australia has only a handful of Ant House Plants but they are worth a second look. Attila Kapitany, an expert grower and observer of all kinds of succulents, describes them – along with bottle trees, salt marsh plants and other local fleshy plants – in his book on Australian succulents published a couple of years ago.

There are two kinds of Ant House Plants in Australia. The Buddha-like ones, from the coffee family (Rubiaceae), and a climber with swollen, ‘ant house’ leaves in the milkweed family (Apocynaceae).

The Buddhas grow mostly near the coast, and typically, but not exclusively, in melaleuca, the paperbark tree. Their roots are wrapped around the tree branch so they survive on direct rain and moisture in the air. The Ant House Plants don’t sit in the forks of trees like bromeliads and many other epiphytes, but are strung along the branch connected only by ant trails.

The small, dull, and barely open flowers appear through holes in the swollen stem. Within the stem there is a network of tunnels, some for the ants to live, some to store food, some for air holes, and so on. This elaborate infrastructure is provided by the plant, which gains valuable nutrients in exchange.

In the Tropical Centre at Sydney's Royal Botanic Gardens we have species of Myrmecodia and Hydnophytum, some from Cape York in Australia.

We also have the other kind of Ant House Plant. Dischidia major is a creeper with two kinds of leaves. Disc-like regular leaves plus angular swollen leaves called ‘pitcher leaves’. Although it sounds like they collect water, they are really a home for ants, and even more intriguingly, the roots of the plant!

This could also be called the inside-out plant. The roots are attracted into the cavity inside the leaf to take advantage of the nutrients provided by the occupying ants.

Image: A ‘Buddha-like’ Ant House Plant in the Tropical Centre at Sydney's Royal Botanic Gardens, next to a labelled orchid (Bulbophyllum). *This story is from the Radio Archives (September 2007).