Rubiaceous Ant Plants (Six on Saturday #17, November 25, 2017)

After a couple of weeks absence, here’s another Six on Saturday.  As with previous posts on Pachypodium and Nepenthes, I’m focusing on a single group of greenhouse plants this week.

platytyrea-mossman
Myrmecodia platytyrea (Mossman Gorge form) overflowing a 5-inch pot

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.

Section1
Myrmecodia tuberosa cut to reveal interior chambers (a photo from my defunct ant plant website, ca. 1998)

 

section3
Closeup of chambers.  Arrows indicate two warted chambers.  Smooth chambers can be seen at the center of the slice.

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.

platytyrea-mossman-stem

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”

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.

3Myrmecodia tuberosa

tuberosa

tuberosa-stem

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

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

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.

formicarum1
Hydnophytum formicarum.  A large form from Thailand with entrance holes generally restricted to the underside of the tuber.  The tuber is partially obscured by moss growing up its sides and is larger than it appears.  This plant is twenty-one years old and was the first ant plant I grew from seed.
cf_formicarum1
Hydnophytum cf. formicarum. A plant distinguished by its very broad leaves and smaller tuber with proportionally very large entrance holes.
cf_formicarum-Belum
Hydnophytum cf. formicarum from Belum rainforest, peninsular Malaysia.  This is a dwarf form with brown, flattened tuber and tiny leaves barely as long as those of the Thai form are wide.  Notice the the small entrance hole on the right and pores on the lumpy region at left.

So, that’s six rubiaceous myrmecophytes.  For more Six on Saturday that is perhaps a little less botanically grotesque, head over to The Propagator.

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13 thoughts on “Rubiaceous Ant Plants (Six on Saturday #17, November 25, 2017)

  1. A group of plants I’ve not heard of before and stand no chance of ever growing but totally fascinating to learn about. Something to read more about to fill those long, cold, winter evenings we’re about to get hit with. I think I’ll start a “Plants I Want to Read About” list to accompany the “I want” list (which I’ve now frozen at 23 for next year). Thanks for this six.

    Liked by 1 person

    1. That’s a good idea, and less expensive than the want-to-buy list—although there’s always a risk of plants moving from one list to the other.

      I’m hoping that other blogs will give me ideas for plant books to read when the weather is grotty. A series of short book reviews might be a good idea for a winter Six on Saturday.

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    1. That’s a large part of their appeal. It is completely mindboggling. I would suspect the tuber originated as a water storage organ, and ants probably sheltered underneath, since nesting sites would be limited in the trees. The existing ant plants vary in the complexity of their chambers, so one can almost envision some of the intermediate steps.

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  2. Very interesting Six! I have never heard of these plants either and the documentation and the stuff are fascinating. . Why am I answering today? … because of your last six (9-12) on the books. For me, as French, none of them I can read … so I went back to the past to discover your blog 😀

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