Ant Plants

By Bob Harris (April 2005)

When you hear the words “ant plant,” you know exactly what the plant is, don’t you? Sure, we see them in the HSCSS cactus show annually.

A University of Connecticut website answered a Google online search request with a long listing of “ant plants,” which included:

Acacia collinsii, cornigera and hindsii – Fabaceae
Dischidia major and rafflesiana – Asclepoadaceae
Hydnophytum formicarum and species – Rubiaceae
Lecanopteris mirabilis – Polypodoaceae
Monolena primulaeflora; Myrmecodia platyrea, solomonensis and tuberose – Rubiaceae
Schomburgkia tibicinis – Orchidaceae
Solanopteris brunei – Polypodoaceae
Tetrastigma voinierianum – Vitaceae.

All the above plants have symbiotic relationships with ants. Some of these plants are caudiciforms – another not on the list is Macleania insignis, in the Ericaceae family.

Hydnophytums and myrmecodias are found from Thailand to Fiji. Their stems enlarge into a tuber with chambers inside. The chambers have entrance holes which allows ants access. Nutrients released by decay of the ants’ waste (mostly leftover insect pieces) are absorbed by special “warts” inside the chambers.

Myrmecodia species have separate smooth-walled chambers that ants inhabit and warty chambers that serve as debris dumps. In hydnophytums, the chambers are less specialized, and the warts tend to be concentrated toward the ends of the chambers.

So the ants provide nutrition and the plant provides shelter. Even though the plants have a caudex or tuber, they are not necessarily succulents. Their culture and indigenous area do not seem to reflect succulents.

The acacias provide shelter inside their thorns, and the ants in return protect the plants from browsing animals and bugs, which might eat their leaves. Some even clear the area around the trunks of plants, eliminating growing competition.

Some of these plants could be considered succulents or at least caudex plants. It is easy to see why the botanical names are important when ordering or identifying plants.

Missouri Botanical Garden has an exhibit of ant plants in the Climatron. It is located along the outside railing near the location of the old cactus house. There is also an acacia and ant exhibit in the educational section of the Climatron.