The mountains of western Thailand and Myanmar are home to a long described, yet rare species of cane orchid, Thunia bensoniae. This genus, totally confided to southeast Asia, has only 6 known species and a handful of hybrids. These orchids have a bamboo-like look about them, and are deciduous in the winter months. T. bensoniae is one of the more showy species, sporting large Cattleya-like purple/pink flowers.
In late winter or early spring new growths sprout from the base of completely leafless, sheath covered canes. These canes are dark brown and life-less looking. Their base is slightly bulbous and by winter’s end the previous season’s roots are all dead. The curious new growths start as bunches of short leafy bracts and are a light blue green color. As the season progresses, they expand to form an elongated cane-shaped growth with 10 or more lanceolate, yet broad leaves, soft to the touch. The newly formed cane within remains relatively soft as well until full maturity in the fall at which point it hardens off, becoming tough and fibrous.
At the end of their growing cycle buds form at the terminus of the cane. Each cane can sport up to 5 large flowers. The flowers are very showy, yet hang every which way, especially downward. The word “floppy” comes to mind. Not surprisingly, they are best viewed from below. They give off what might be termed an acrid odor – thankfully it is not very strong.
Each flower has the classic orchid blossom shape, as in the genus Cattleya, and is purple/pink. The lip is tubular, with a broad trumpet shape and is lightly frilled with many striations on its inner surface. The inner surface is also covered in yellow-orange tufts and ridges (lamellae) – an aid to ensure pollination. The remaining flower segments are very similar in shape and length and usually are a much paler color than the lip itself, but can be edged in dark purple/pink. In nature they are said to flower in early summer, however, at my house they start growth later than in their native homes and so don’t flower until mid summer.
By late fall the leaves begin to die back. This is not necessarily a function of colder weather, but rather is a natural cycle of their growth. By Christmas time they are fully deciduous and remain dormant for 3 or more months.
Thunia bensoniae is native to the western mountains of Thailand and adjacent areas of Myanmar. Some sources list it also native as far east as India and into southern China, but I cannot confirm this.
In nature it can be found growing terrestrially, lithophyically, and epiphytically in monsoonal forest. It is said that the roots of plants growing epiphytically are in thick mats of moss and roots of other epiphytes and not on bare bark. The canes typically grow at a ninety degree angle from their perch or hang down at a slight angle.
I first grew this species two years ago when a friend in Thailand sent me a couple plants. They were in complete dormancy, and except for a trace of green on the bulbous base of the canes, they appeared completely life-less. I called my friend and he laughed and said, “Ah, Thunia are tough as old boots. Don’t worry, they will grow.” I wasn’t much reassured by this, but planted them out in pure sphagnum moss with the hope they might revive. Some weeks later I was surprised at finding new, chubby growths at their bases.
As the plant develops you wonder where the heck it is getting its energy from to put on such impressive growth. New leaves form quickly along the developing cane and roots shoot out in large masses off the base of the new canes. I have found sphagnum to be an excellent choice for growing roots on these plants. By midsummer the flower sheaths begin to form at the end of the newly grown canes.
The flowers themselves are not a disappointment, but their odd hanging habit is a bit disconcerting. At first I tried to stake the canes in an upward position, but found the flowers oriented themselves any which way – some hung downward and even flopping backward such that they presented themselves upside-down. Clearly, staking wasn’t a good idea. Another plant I allowed to develop naturally, with the canes hanging nearly perpendicular to the ground. This plant’s flowers hung in a more natural manner.
I’ve found this plant to be straightforward in cultivation. In the winter the canes should be kept cool and relatively dry. In early spring I repot them into fresh sphagnum and begin to water them frequently. Soon the new growths begin and at this point I fertilize on a regular basis to ensure plump canes. The mature leaves are rather soft and easily damaged by the elements and insect attack. For that reason I grow them either inside or in a protected place near the eves of my house. Like other orchid plants from monsoonal rain forests, it requires high humidity at all times when in growth. One thing – though this plant hates dry winds it also needs lots of air movement or leaf rots easily form. When in growth keep it on the warm side – between 20 and 30 C being optimal. In winter the dormant canes can handle nearly freezing temperatures, but warmer is better.
Propagation of Thunia is supposed to be easy as well. It is said that all you need do is cut an old cane up into pieces such that each has a leaf node. Place these “cuttings” onto a moist surface and new plants will grow out from the nodes. I have not tried this since I have only two plants, but I have noticed that occasionally new plants (called keikis in orchids) will form on uncut canes, usually in late summer or early autumn. I have so far been unsuccessful in separating them to make new plants however – they seem quite tender.
All in all, this is a neat orchid species to keep. Given its relative rarity and somewhat odd flower positioning though, I’d say it will remain mostly a plant for species nuts – self included.