Tsukuba National Botanic Gardens in Ibaraki, part of the Tokyo National Museum, were opened to the public in October 1983. The garden, which covers 14 hectares, was constructed primarily for experimental research and for botanical education. Divided into 14 different plant zones, it contains approximately 4,000 species of plants. Trees, shrubs and herbs (both perennial and annual) are grown in conditions as close to natural as is possible.
|An endangered species, the jade vine has flourished and propagated — with a little help — at the Tsukuba National Botanic Gardens.|
If you’d like to know more about Japanese flora, this garden is a must, and repeated visits over the seasons should provide a much better understanding of the country’s diverse flora.
In the garden’s fine tropical greenhouse is the jade vine (Strongylodon macrobotrys), a climber native to the tropical rain forests of the Philippines. The common name is derived from the purple color of the seed pods. Other English names include Gray’s jade vine (after Asa Gray [1810-1888], the American botanist who described and named this vine in 1854) and emerald creeper. In Japanese it is known by the name hisuikazura and also by the katakana form makurobotorisu.
The jade vine actually belongs to the pea family (mame-ka, Leguminosae). It has some 27 recognized species, naturally distributed from Madagascar across the islands of the Indian Ocean, including Sri Lanka, New Guinea and the Philippines. The generic name, Strongylodon, comes from strongylos, the ancient Greek word meaning round, and odous, a tooth, referring to the rounded teeth found on the flower’s calyx. The species name, macrobotrys — “large grapelike clusters” — refers to the seeds’ appearance.
The jade vine can climb up to 40 meters. Its bluish-green flowers are borne in long hanging racemes, as much as 90 cm long. Its leaves are dark green and trifoliate, with individual leaflets 12.5 cm long.
In its natural habitat in the Philippines, S. macrobotrys is in grave danger of extinction. The vine only grows in the deepest, darkest tropical rain forest, which is being felled for timber.
This endangered species of Strongylodon was first introduced from Singapore in 1964 to Koishikawa Botanical Garden in Tokyo (Japan’s oldest botanic garden), and cuttings were given to Tsukuba Botanic Gardens. The plant flourished, flowering well every year, but failed to produce any seed. The Tsukuba botanists then conducted a histological examination.
A close examination of an individual flower reveals a slightly protruding stigma and anthers at the keel-shaped petal’s apex. The researchers found that pollen (male gametophyte) from the anthers’ pollen sacs was deposited on the tip of the stigma at flowering time. The pollen grains failed to enter the stigma, however, because of the presence of a dome-shaped cuticle layer, so the botanists artificially broke this cuticle. They found that if the flower’s base is lightly squeezed, it will push down the base of the stamen and pistil, and the stigma and anther will protrude together and rub off the pollinator. Clearly, the jade vine is dependent on an insect or animal to pollinate its flowers — but what?
To discover the answer to this question, plants were sent to Nagasaki Bio-Park, where a tropical ecosystem has been artificially reproduced in a dome-shaped greenhouse. Among the bird life in the dome was the scarlet parrot (Eos bornea), and in due course, by careful observation, it was caught in the act of pollinating the jade vine. Whether the same bird is responsible in the wild is still unknown, but as a case study it is instructive: The protection or propagation of rare plants is not enough, as whole ecosystems are necessary for endangered plants and animals to survive. As the case of the jade vine shows, botanists still have much to discover about the plant kingdom.
Tsukuba National Botanic Gardens are located in Tsukuba Science City, Ibaraki. Take the JR Joban Line from Ueno to Tsuchiura Station. Immediately outside the station, board the Kanto-Tetsudo bus bound for Tsukuba Technopark and get off in front of the botanic gardens. Admission is 210 yen for adults, 60 yen for children. Open daily 9 a.m.-4:30 p.m. except Mondays. For further information, call (0298) 51-5159.
Here’s a new plant for your garden. The common English name is kenaf, but it is also known as ambari, Deccan hemp and Bimlipatum jute. Introduced to Japan in the last four or five years, it is called kenafu in katakana here. The botanical name is Hibiscus cannabinus, from the hemplike leaves, but despite the resemblance there is no point in trying to smoke them.
Its yellow or pale purple flowers with a red-purple blotch at the base appear in late summer. Probably the tallest annual cultivated in Japan, it will grow to well over 2 meters. Native to tropical Africa and long cultivated in India, China and southeastern Europe, kenaf’s virtue is its prickly, fibrous stem, from which cordage and sacking have long been made; it is now used increasingly to make paper, and promises to be stronger and cheaper than wood pulp paper. In addition, its seeds yield high-quality oil.
Kenaf is easily cultivated from Hokkaido to Okinawa, whether as a commercial fiber crop or a potted plant on a balcony. In spring or early summer young plants are sold in garden centers. No special soil is required, but it does best in a sunny location. Next spring perhaps you can grow some in your own garden, while reflecting on the fact that kenaf fiber could help save the rain forests.