The epiphytic myrmecophytes (ant plants) of the coffee family, Rubiaceae, are surely some of the strangest plants that grow anywhere in the world. Their overall appearance is often grotesque: gray or silver or brown blobs with thick, armored stems and sharp spines derived from modified roots. They cling to tree trunks or hang upside down below horizontal branches, looking like aliens that have inexplicably settled in an Asian forest. And to top all of that, their real strangeness is hidden inside. Soon after a seedling ant plant germinates, the hypocotyl–the stem below the cotyledons–starts to swell into a tuber. As the plant grows, tissue within the tuber dies in a genetically programmed manner, first forming a hollow space and then expanding into a series of tunnels and chambers. The tunnels are connected to the outside by entrance holes around the base of the tuber, and the chambers are often aerated by pores.
All of this baroque development is for the benefit of symbiotic ant colonies who set up housekeeping in the artificial nest that the plant has grown. Both insects and plant benefit from the relationship. The ants get a secure home, and the plant is fed by the ants. The ants live in smooth-walled chambers and deposit leftover fragments of insect prey and other waste in chambers with wart-like excrescences on the walls. As the waste decomposes, the plant absorbs nitrogen through the warts.
The natural range of the rubiaceous ant plants extends from Thailand to Australia and east as far as Fiji, but the greatest diversity is found on New Guinea. In the mid-1990s, when I first became interested in ant plants, only about five species were in cultivation, and they were very hard to find. With some effort (i.e. obsessive searching), I managed to connect with a few other like-minded growers via email and traded seed and seedlings with the curators of several botanical gardens. These days, the plants are (somewhat) easier to obtain, and a wider range of genera and species are in cultivation thanks to the efforts of a handful of hobbyists and nursery owners from around the world. Several nurseries in Europe and the U.S.A. sell seedlings, and plants are occasionally available on eBay.
So without further ado, here are six (on Saturday) ant plant species:
1. Myrmecodia platytyrea (Mossman Gorge form)
The plant shown at the top of this post is a very vigorous Myrmecodia descended from material originally collected in northern Queensland. Like most of the rubiaceous ant plants in cultivation, M. platytyrea has flowers that self-pollinate, so seedlings remain true to type over multiple generations. The Mossman Gorge form of M. platytyrea produces long, sharp spines and very vigorous roots that often invade the pots of its neighbors. Its leaves are narrower and more succulent than other cultivated M. platytyrea descended from plants collected in New Guinea.
The shield-like leaf bases on the stems of M. platytyrea are called clypeoli. The spines bordering the clypeoli hide alveoli, pits in which the small white flowers develop and from which the orange fruit protrudes when ripe.
2. Myrmecodia sp. “Pink Fruit”
This species has very strong sharp spines and pink fruit. It is commonly cultivated by ant plant enthusiasts, but its origins are obscure. Possibly, it is M. tuberosa ‘Papuana’ which grows in New Guinea and northern Australia.
3. Myrmecodia tuberosa
This is the most variable and widespread Myrmecodia species, with a range extending from Malaysia to Australia. The form shown here does not have strongly developed clypeoli, so you can easily see the elongated alveoli filled with papery bracts.
4. Myrmephytum beccarii
Myrmephytum is a genus of five species found in the Philippines, Sulawesi, and western New Guinea. M. beccarii is from the Philippines, and was introduced into cultivation in the U.S. around 2006.
5. Hydnophytum moseleyanum
H. moseleyanum is a lowland species from New Guinea and Australia. Hydnophytum species usually lack spines and have many elongated branches without clypeoli and alveoli. Their chambers are less complex than those of Myrmecodia. Note the large entrance hole on the side of this tuber. Above and left of the entrance hole, a patch of papery dead tissue is peeling away to reveal a new hole.
6. Hydnophytum formicarum
A very variable and widespread lowland species from Thailand, Malaysia, and Indonesia. Several different forms varying in size and color are in cultivation.
So, that’s six rubiaceous myrmecophytes. For more Six on Saturday that is perhaps a little less botanically grotesque, head over to The Propagator.