Rhynchostylis Gigantea (Lindley) Ridley - ช้างกระ

ORCHID SPECIES CULTURE
by Charles and Margaret Baker

AKA: Saccolabium giganteum Lindley, Vanda densiflora Lindley, Saccolabium harrisonianum Hooker, Saccolabium albolineatum Teijsmann and Binnendijk,Vanda densiflora var. petotiana Rchb. f., Vanda hainanensis Rolfe, Anota densiflora (Lindley) Schlechter, Anota harrisoniana (Hooker) Schlechter, Anota hainanensis (Rolfe) Schlechter, Rhynchostylis gigantea subvar.petotiana (Rchb. f.) Guillaum, Rhynchostylis densiflora (Lindley) L. O.Williams, Anota gigantea (Lindley) Fukuyama, Rhynchostylis gigantea var. harrisoniana (Hooker) Holttum.

ORIGIN/HABITAT: Burma, Thailand, Malaya, Laos, Cambodia, Vietnam, China, Borneo, and Indonesia. In Burma, plants grow near Rangoon and Toung-ngoo as well as elsewhere in the north, but they are not found in the Tenasserim Provinces in the south. In Thailand, plants are found throughout most of the mainland from the eastern areas around Prachinburi northward through Nakorn Sawan and Loei to near Chiengmai in the north, where plants have been collected at 870 ft. (265 m), they are also found in the Kanburi district in the southwest, just north of peninsular Thailand. In Malaya, plants are known to grow in Singapore and surrounding islands. In Laos, plants are found on the Vientiane Plain and in the Bolovens region. In Cambodia, Rhynchostylis gigantea has been found on Mt.Camchay. In Vietnam, it is known from near Ho Chi Minh City (Saigon) and near Quangtri. In China, the type specimen for Vanda hainanensis was found on Hainan Island. In Indonesia, plants grow on Anambas Island and other
islands in the China Sea. In Borneo, plants are found in the lowlands at numerous locations.

Cultural Recommendations:

LIGHT: 3000-4000 fc. Light should be bright but indirect light may be best, and full mid-day sun might sunburn the plant. Strong air movement should be provided at all times.

TEMPERATURES: Summer days average 90-91F (32-33C), and nights average 76-77F (24-25C), with a diurnal range of 14F (8C). The warmest temperatures of the year occur in spring during the relatively clear weather at the end of the dry season. Spring days average 93-95F (34-35C), and nights average 76-78F (24-26C), with a diurnal range of 16-17F(9-10C).

HUMIDITY: Near 80% most of the year, dropping to 70-75% in winter and early spring.

WATER: Rainfall in the habitat varies from heavy to very heavy starting in late spring and lasting into autumn. Averages then decrease rapidly into the dry season that lasts for 3-4 months in winter and early spring. Cultivated plants should be watered heavily while actively growing, but aeration around the roots must be excellent, allowing the roots to dry rapidly after watering. For plants grown in pots or baskets, the medium must never become water logged or soggy.

FERTILIZER: 1/4-1/2 recommended strength, applied weekly when plants are actively growing. Many growers prefer to use a balanced fertilizer throughout the year, but others use a high-nitrogen fertilizer from spring to midsummer, then switch to a high-phosphate formula in late summer and autumn.

REST PERIOD: Winter days average 88-91F (31-33C), and nights average 68-73F (20-23C), with a diurnal range of 18-21F (10-12C). Although these temperatures are fairly common throughout the range of distribution, plants from northern Thailand and Burma commonly experience winter minimum temperatures 8-10F (4-6C) cooler than indicated, so cultivated plants should adapt to winter night temperatures as low as 60F (16C) to as warm as 70F (21C). Rainfall in the habitat is low for 3-4 months in winter and
early spring. Humidity remains relatively high, however, so some moisture is available from heavy dew and late-night mist. Cultivated plants need less water in winter, and they should become rather dry between waterings.

If winter humidity in the growing area is high, an occasional early-morning mistings between infrequent light waterings should provide sufficient moisture in most growing areas. If humidity in the growing area is low, however, the early-morning mistings should be increased. Plants should never dry out completely. Fertilizer should be reduced or eliminated until heavier watering is resumed in spring.

GROWING MEDIA: Rhynchostylis are reported to be singularly intolerant of stale conditions around the roots but neither do they like being disturbed for repotting. They are, therefore, best grown in a manner that allows the numerous aerial roots to hang free. Growers may place them in wooden baskets without any supplemental potting medium or else mount them on tree-fern or cork slabs with no padding around the roots. If grown in this manner, however, humidity must be high and plants should be watered at least once daily in summer and plants may need several waterings a day
when conditions are hot and dry. Because many growers have trouble keeping their plants adequately moist, they are often grown in pots or baskets using a very open, fast draining medium, which allows the roots to dry rapidly after watering. Using a mixture of medium- to large-sized fir bark with an equal amount of medium- to large-sized hardwood charcoal produces good results. Charcoal may be used alone.

Rhynchostylis do not respond well when disturbed, but if plants are grown in a container filled with a bark mix, they should be repotted every year because any break-down of the medium will cause a rapid decline of the root system. Because the
inflorescence emerges at the base of the stem, plants should be placed high in the pot. Plants become reestablished faster with less stress if they are mounted or repotted just as new root growth is starting. See also the note under Flowers.

MISCELLANEOUS NOTES: The bloom season shown in the climate table is based on cultivation records. In the habitat, plants normally bloom in winter.

Plant and Flower Information:

PLANT SIZE AND TYPE: A fairly large, 24 in. (61 cm) monopodial epiphyte.

PSEUDOBULB/STEM: Up to 4 in. (10 cm) long. The stem is robust but very short. It is densely leafy and produces numerous very stout roots. Stems frequently branch, however, and older, well-grown plants may be have many stems.

LEAVES: To 12 in. (30 cm) long by 2-3 in. (5.0-7.5 cm) wide. The dark green, strap-shaped leaves are very thick and leathery, unequally bilobed at the tip, and frequently marked with prominent, pale green, longitudinal stripes.

INFLORESCENCE: To 15 in. (38 cm) long. The pendulous, densely flowered spike emerges from the stem at the base of the leaves.

FLOWERS: Up to 50 on each inflorescence. Aa medium-sized plant may produce 3-4 inflorescences, and a large, well-grown plant may produce even more. Kamemoto and Sagarik (1975) reported that in Bangkok a large, many-branched specimen has produced as many as 30 flower spikes. Individual flowers are 1.0-1.5 in. (2.5-3.8 cm) across. The waxy blossoms are highly fragrant and last about 2 weeks. Flowers usually are white, with red-violet, amethyst-purple, or magenta spotting, and they often have
a well-defined apical blotch of the same color. The lip is red-violet, amethyst-purple, or magenta which usually fades to a whitish color at the base and toward the middle. Some all white clones have been found, and very occasionally, plants with all red flowers are found.

Sepals and petals are elliptic-oblong, spreading, more or less sharply pointed, and often rather wavy. Sepals are about 0.6 in. (1.5 cm) long by 0.3 in. (0.8 cm) wide. Petals are about 0.6 in (1.4 cm) long by 0.2 in.(0.5 cm) wide and are widest near the apex. The almost oblong lip is 3-lobed at the apex with small, rounded lateral lobes and a much smaller but also rounded midlobe. The blade of the lip is 0.5 in. (1.2 cm) long by 0.3 in. (0.7 cm) wide, fleshy, and slightly hairy. It points straight
forward, is nearly oblong, and widens somewhat from the base. The disc consists of 2 hairy ridges that descend into the spur. The short spur, which is 0.2-0.3 in. (0.6-0.7 cm) long, is inflated but somewhat laterally compressed, backward-pointing, and bluntly tipped.

Red-flowered clones have been crossed with other red clones by growers in Thailand. About 80% of the progeny produced by this breeding were red, which has resulted in red clones being more readily available. Kamemoto and Sagarik (1975) reported that the red color of these flowers is affected by temperatures preceding the flowering season. When autumn temperatures are warmer than normal, the red coloring does not develop fully and some of the normally red-flowered plants will produce flowers
with large white blotches.

HYBRIDIZING NOTES: The chromosome count is 2n = 38 as reported by Kamemoto and Sagarik (1975). They further stated that compared to plants from other regions, those from near Chiengmai in the north have heavier stems; shorter, thicker, and darker green leaves; and larger flowers, even though the chromosome count is the same as plants from other regions.

REFERENCES:

Bechtel, H., P. Cribb, and E. Launert. 1980. Manual of cultivated orchid species. MIT Press, Cambridge, Mass.
Hamilton, R. 1988. When does it flower? 2nd ed. Robert M. Hamilton, 9211 Beckwith Road, Richmond, B.C., Canada V6X 1V7.
Hawkes, A. [1965] 1987. Encyclopaedia of cultivated orchids. Faber and Faber, London.
Kamemoto, H., and R. Sagarik. 1975. Beautiful Thai orchid species. Orchid Society of Thailand, Aksornsampan Press, Bangkok, Thailand.
Pridgeon, A. ed. 1992. The illustrated encyclopedia of orchids. Timber Press, Portland, OR.
Seidenfaden, G. 1988. Orchid genera in Thailand XIV. Fifty-nine vandoid genera. Opera Botanica 95, Copenhagen, Denmark.
Seidenfaden, G. 1992. The orchids of Indochina. Opera Botanica 114,Copenhagen, Denmark.
Seidenfaden, G., and J. J. Wood. 1992. The orchids of peninsular Malaysia and Singapore. Published in association with The Royal Botanic Gardens, Kew and Botanic Gardens, Singapore. Olsen & Olsen, Helstedsvej 10, DK-3480 Fredensborg, Denmark.
Wood, J. J. and P. Cribb. 1994. A checklist of the orchids of Borneo. Royal Botanic Gardens, Kew.

Copyright 1999, Charles O. Baker and Margaret L. Baker
Sheet version 64817872

ช้างกระ

ชื่อวิทยาศาสตร์ : Rhynchostylis gigantea (Lindl.) Ridl.
ชื่อวงศ์ : ORCHIDACEAE
ชื่ออื่นๆ : เอื้องต๊กโต
อาณาจักร: Plantae
ส่วน: Magnoliophyta
ชั้น: Magnoliopsida
ตระกูล: Rhynchostylis
สกุล: Vandoideae
สปีชีส์: Rhynchostylis gigantea

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