Plant Hunting in Yakushima

Rhododendron yakushimanum             in cultivationTo many keen gardeners the name Yakushima is known only by association with Rhododendron yakushimanum. This beautiful plant is noted for its unique combination of compact size, good foliage and pristine white flowers that develop from rosy-pink buds. It was described in 1921 but came to the notice of Western gardeners only when awarded a First Class Certificate in 1947 - the clone 'Koichiro Wada', named after its introducer.

Some other good plants from Yakushima, mostly very dwarf alpine variants, have also become established in our gardens, notably Viola verecunda var. yakusimana, Lysimachia japonica var. minutissima, and Shortia soldanelloides var. minima. These horticultural gems give only a hint of the diversity of plants on the island. Its vegetation is far too diverse to do justice to in a brief article, especially one based on a visit of a mere four days, but I hope to give a taste of it.

Map of Yakushima

Yakushima is the small, almost circular dot on the map, 70km south of Kyushu, which is the southernmost of the four main islands of Japan. It is about 27km in diameter -- rather smaller than the Isle of Wight -- yet has 20 peaks over 1,500m, the highest, Miyanoura-dake, being 1,935m. Rainfall is high throughout but varies much with altitude, from 3,000mm to over 7,000mm per annum -- the locals claim they get 35 rainy days in a month. The rainfall certainly is spread throughout the year but with a strong peak in early summer and a relatively dry late autumn and winter. At the time of my visit in November, indeed, there had been no rain for over 40 days, but this is most exceptional.

As the island is predominantly mountainous, the one proper road is confined to the 2-3km wide coastal fringe that is less than 100m in altitude. This road covers about three quarters of the island's circumference but numerous forestry tracks, some partially tarmacadam but most with tyre-shredding loose stony surfaces, twist their way into the mountains to about 1,300m. The local taxi drivers, nearly always friendly and helpful, are happy to deposit hikers at the end of the track and to collect them again in the evening.

The island's population of around 25,000 is scattered among about 20 villages and small towns on the north, east and south coasts. There is little obvious industry apart from forestry, fishing, farming, crafts and, increasingly, tourism. At Nakama in the south-west is Yakushima Fruits Garden and this is excellent indicator of the climate. Bananas of various kinds, passion fruits, guavas and papayas thrive without protection except from the wind. The owner has started producing preserves and here, as elsewhere, freshly-pressed juices are sold. Hardly surprisingly fish, both raw and cooked, predominates in the local food, which is among the most enjoyable I have had in Japan.

Coastal scene near O-no-Aida, Yakushima The most remarkable thing about the island is the range of vegetation types represented in such a tiny area - bear in mind the comparison with the Isle of Wight. A local wild-flower guide includes a stylised cross section of the island alongside a map of mainland Japan (about 1,500km from north to south). Lines link similar vegetation zones: the coastal area below 600m to the warm-temperate broad-leaf evergreen forests of southern Japan, and the mountains over 1,500m to the sub-alpine southern part of Hokkaido. In between, the vegetation parallels that of central and northern Honshu. The comparison is based on annual mean temperatures -- obviously the vegetation matches in broad terms rather than precisely. Indeed, Yakushima is noted for its numerous endemic species and subspecies.

Because of the island's small size, a day's walk can take one with relative ease from luxuriant subtropical coastal scenes to cool temperate mountain vegetation and back again.

Travelling along the coastal road in autumn, the eye is caught by by cultivated and native plants. Bushes of the flamboyant crimson Hibiscus rosa-sinensis seem to mark the approach to each village, whilst the more restrained H. mutabilis forms large, compact bushes with pink and white flowers that deepen in colour as they age. The term 'invasive' took on a new significance for me in a garden that had totally disappeared under dozens of square metres of Thunbergia laurifolia.

A giant specimen of Ficus microcarpa a striking roadside feature at Nakama, its festoons of aerial roots straddling a car-width drive. From bridges over steep-sided ravines, glimpses could be snatched of tree ferns (Cyathea fauriei). In these deep valleys the large number of epiphytic plants emphasises the high rainfall. Branches and tree trunks are dripping with several species of ferns: Pyrrosia lingua, filmy ferns, the narrow pendulous fronds of species of Vittaria and the ubiquitous bead fern (Lemmaphyllum microphyllum). Selaginellas and lycopodiums abound and Hoya carnosa, here near the northern limit of its range, trails and twines vigorously.

Farfugium hiberniflorum in Yakushima On the ground many curiosities await the searching eye: the bizarre parasites Balanophora tobiracola and B. japonica flower in the form of stubby little phalluses, cream and scarlet respectively. Several species of Asarum are here, notably A. yakusimense, with shiny green heart-shaped leaves, and another with often handsomely mottled and speckled leaves and rather dull brownish-purple flowers. Farfugium japonicum (Ligularia tussilaginea) is quite well known in Western gardens in its cultivar 'Aurea Maculata', with rather worrying creamy blotches on the leaves. It was therefore reassuring to see the healthier-looking green-leaved form. More exciting was its ally F. hiberniflorum with beautiful, begonia-like, deeply toothed oval leaves, often with a silvery sheen. Endemic to Yakushima and neighbouring Tanegashima, this also has a branched head of yellow daisies. Another composite, but of very different appearance, is the elegant little Ainsliaea linearis, often growing on mossy rocks. This is loved by those Japanese who love to grow small plants, and its wispy palest pink flowers have a delicate spicy scent.

In any Japanese forest beautiful tree barks may be seen -- Betula, Clethra and Stuartia for example. Here a dramatic addition to the list is a species of Lagerstroemia (probably L. fauriei) forming a moderate tree with red and orange patchwork bark. A curiosity is the apple camellia, C. japonica var. macrocarpa, with shiny red and green fruits 5cm across. Numerous orchids abound, include species of Calanthe, of which only the yellow and white C. venusta was flowering during my brief visit. At low altitudes the shrubby local variety of Acer capillipes, var. morifolius, provided the relief of red and orange autumn colour dotted amongst the lush greenery.

One tree the island is famous for is the yakusugi -- Cryptomeria japonica. Strictly, the name is restricted to gigantic trees of great age in the mountains, for ample at 'Yakusugi land' west of Ambo. Here, at an altitude of about 1,000m, are found many enormous trees including some of the largest the island. The real monsters among these reach 30m in height, with girth at breast height of up to 16m. They are slow-growing, giving a handsome and relatively hard timber of beautiful colour and fine even grain -- the basis of a local crafts industry that produces everything from postcards (wooden veneer) to chopsticks, furniture and figures of Buddha. One local landmark is known as Wilson's stump (uiruson kabu) having been felled in the 17th century, but rediscovered by E.H. 'Chinese' Wilson during his visit to Japan in 1914. These large sugi are very impressive trees and often support a considerable population of epiphytes, including even trees such as Sorbus commixta. The ages stated for such giants vary considerably and many appear to be wildly exaggerated, but the more probable estimates suggest figures of 1,000 to 2,000 years.

In the sugi forests, at altitudes over 600m, are found two species that are fairly familiar in Western gardens as attractive evergreen shrubs - Distylium racemosum in the witch-hazel family and Trochodendron aralioides in its own monotypic family. Interestingly, both are fine trees in their native region, growing to 20m in height. The Trochodendron has a curious habit of growing almost as a 'strangler', often on Cryptomeria, with numerous large sinuous roots tightly embracing the lower two to three metres of the sugi.

Mountain scenery from Kuromidake, Yakushima

In the upper parts of the sugi forest, at Hana-no-Ego for example, the trees become much smaller. Many sun-bleached dead or near-dead ones stand out on the hillsides, the latter an inspiration to bonsai enthusiasts. Particularly striking among them is Daphniphyllum macropodum, whose crimson-stalked leaves appear whorled at the branch tips. Similar foliage of Rhododendron metternichii appears to intergrade with R. yakushimanum at still higher altitudes -- indeed most Japanese botanists consider the latter to be a variety of the former rather than a distinct species. In autumn, there is good colour -- the pink and red leaves and red or black berries of Viburnum furcatum; the yellow leaves of the daphne-like Wikstroemia kudoi; the small ericaceous shrub Tripetaleia paniculata with leaves aflame, near the pale yellow of Hydrangea anomala subsp. petiolaris, both often found clinging to exposed rock faces.

An alpine meadow scene and a welcome fresh breeze greet the weary hiker as he emerges from the last of the forest. Here is a patchwork of Juniperus chinensis var. sargentii, Rhododendron yakushimanum and Pseudosasa owatarii (an endemic dwarf bamboo) all forming a low scrub, interspersed with a narrow-leaved dwarf Miscanthus. Also among these are found the tiny Smilax biflora whose leaves and shiny red fruits are only 5 to 10mm in diameter; and an equally dwarf rose, Rosa onoei, with straight prickles, tiny lanceolate leaflets that turn scarlet before falling and heps 5mm in diameter. This local form has been separated as R. yakualpina but is not always recognised as distinct.

On the upper slopes of Miyanouradake, the tallest peak, which I did not visit, very dwarf forms of Rhododendron keiskei occur, from which the clone 'Yaku Fairy', now well established in our gardens, was selected. Elsewhere, it forms a taller and more lax bush. Another high mountain speciality, which flowers in August, is the handsome Gentiana yakushimensis: alas, although I was on the right mountain I did not see it. Some consolation came in the diminutive form of Shortia soldanelloides var. minima, with very glossy purple-brown leaves 6-8mm wide. Sharing its crevice in a rock were two unlikely congeners: a small polypody fern with an undivided fleshy frond, and a plant of the local race (var. platypetala) of Alectorurus yedoensis, a liliaceous plant with flower stems 10cm tall bearing very small brown-tinged white flowers. Tufts of rather leathery oblanceolate leaves nearby belonged to its ally Aletris spicata.

From the bare granite summit of Kuromi-dake, the northern coast could glimpsed as the mountain mists dissolved and re-gathered. It is only 13km away as the crow might fly but, terms of its climate and plants, almost like another continent.

The beauty of Yakushima and its plants is breathtaking in its diversity and is an obvious cliché to liken it to a jewel or pearl. The local economy will undoubtedly benefit if the tourist trade (at present, mainly visitors from mainland Japan) continues to expand. However, by its very nature this is a fragile jewel and much could be irretrievably lost to uncontrolled development. It is somewhat reassuring to know that the central third or so of the island is part of the Kirishima-Yaku National Park which, it is to be hoped, will provide adequate protection for the delights and treasures of the island and do much to conserve its very special ecosystems.

My visit to Japan was encouraged and assisted by the Royal Horticultural Society. To the Society and to the friends who helped me so much in Yakushima I am deeply grateful.

This article was first published in The Garden 114 (12): 598-604 (1989)