Autumn in Japan is a colorful season, and not only because of the famed koyo foliage of its trees. In gardens, fields and roadsides, too, flowers burst forth as if to celebrate the return of sensible weather after the long, sweaty rigors of summer. However, some of the best-known blooms of this fall season aren't native plants at all, but alien species from the Americas and China.

Perhaps foremost among these are kosumosu (cosmos), beautiful multihued flowers that really bring joy to people's hearts. Easy and trouble-free to cultivate all over the country, cosmos thrive in sunny spots with fertile, well-drained soil. And if you're ever in the southern Hyogo Prefecture city of Takarazuka around this time of year, the dwarf cosmos along its river banks, and the fields and fields in the area given over to cultivating cosmos, are truly a sight to behold.

However, cosmos, a member of the chrysanthemum family (Compositae), is native to faraway Mexico, with an estimated 28 to 30 species in its natural range from Arizona south to Bolivia. This explains why its name, derived from kosmos, the Greek for "beautiful," was bestowed by a Spanish priest in 1791 -- and why its common (though now rarely used) name is Mexican aster.

Having been introduced to Japan during the Edo Period via Europe, nowadays the most commonly cultivated species is C. bipinnatus, an annual whose botanical name refers to the delicate, lacelike foliage. Among the numerous cultivars offered for sale, one of the most popular is dwarf cosmos, which only reaches 25 to 30 cm high -- compared with the regular 2 meters -- and is ideal for balcony gardens.

The featherlike leaves of C. bipinnatus are up to 11 cm long and bipinnate, meaning they are bisected twice, while the flowers are 6 to 10 cm wide and range in color from white through pink to red. In fact, the flowers are composed of two parts, an outer row of eight petals known as ray florets whose function is to attract pollinating insects, and numerous tiny male and female tube florets in the center of the flower.

During the Taisho Period (1912-26), more colors were added to the cosmos palette in Japan with the introduction of kibana-kosumosu (C. sulphureus), whose blooms range from rich orange to pale yellow-red; while chocolate cosmos (C. atrosanguineus) is another more recently introduced perennial species whose flowers, borne on meter-high stems, are vanilla scented and deep velvety black to maroon in color.

Fast and bulbous

Meanwhile, another contribution from the Americas -- this time originally from further south, in marshland around the River Plate in Argentina -- is the indestructible tama-sudare (fairy lily; Zephyranthes candida), whose family name derives from the Greek words meaning "west-wind flower," while the species-name candida comes from the Latin for "white and shining."

Tama-sudare is a bulbous plant that likes full sun and a moisture-retentive soil. Between July and October, it bears snow-white flowers 4 to 5 cm wide on 30-cm stems, with each flower having six petals with six golden stamens in the center. Interestingly, the plant does not produce seed, but instead reproduces through its readily multiplying bulbs.

Before coming to Japan, I had never seen or heard of shion (Aster tataricus), but I soon came to love this autumn-flowering perennial. The botanical name "aster" comes from the Latin for "star," in reference to the flowers' shape.

Like cosmos, aster belongs to the Compositae family, though its origin is not across the Pacific, but nearer at hand in China, from where it was brought long ago in the Heian Period (794-1185). Nowadays, cultivation is centered on the Chugoku region of western Honshu, and also on Kyushu.

What I like about this aster is its stately, 1 to 2 meter height and its attractive purple to blue daisylike flowers in the form of flat-topped corymbs. Each flower is 3.5 to 5 cm in diameter and, like the cosmos flower, it has an outer row of ray florets and a center made up of numerous tube flowers. Shion asters grow well in full sun and soil rich in leaf mold -- and as an extra bonus for gardeners, they are not invasive. Propagation is by dividing plants in spring or autumn.

However, some people believe the shion aster was traditionally grown here not only for its flowers, but also for its medicinal value. As was first mentioned in Chinese medical literature in AD 200, the roots yield a medicine known as zi-wan in Chinese. This is extracted by boiling and is a stimulant, expectorant herb for the bronchial system that helps clear infection and is often taken raw with honey to increase the expectorant effect.

Another familiar autumn bloom here is the shumeigiku or kibune-giku (Japanese anemone; Anemone hupehensis var. japonica), which is also a very popular plant with gardeners in the British Isles. Indeed, no garden should be without this wonderful Chinese perennial that has been growing on these shores, too, for hundreds of years. However, those of you with balcony gardens, be warned: Shumeigiku will not be your easiest flower to grow, as really it prefers soil enriched with lots of leaf mold.

Shumeigiku and its numerous cultivars, including semidouble-flowered forms, bloom between September and October, when the plant will be 50 to 80 cm high and displaying a heavy crop of its characteristic leaves with 3 to 5 lobes. The flowers themselves, however, have no petals, but instead the sepals are modified into petaloids, of which around 30 make up every bloom. Though shumeigiku cannot produce seed, propagation is easy by plant division and by taking root cuttings in spring.

Finally, two more imports from the Americas that add to the autumn colors in Japan are the perennials kiku-imo (Jerusalem artichoke; Helianthus tuberous) and inu-kiku-imo (H. strumosus). Both these species of sunflower in the Compositae family were once widely cultivated as fodder crops, and for human food in wartime, while in the United States the tubers of Jerusalem artichokes are sold as "sunchokes."

Naturalized in style

Altogether there are estimated to be 70 species of Helianthus native to North and South America, though both these species have now naturalized in this country and can even be found growing outside the Imperial Palace on the banks of the Sakurada-bori Moat.

Unfortunately, though, kiku-imo is not a plant that is suitable for balcony gardens, as it is very vigorous and grows to an average height of 1.5 to 3 meters. However, as sunflowers go, the golden-yellow flowers are small, being only 6 to 8 cm across with 10 to 20 outer ray florets surrounding numerous tube flowers.

It all makes for a delightful, if (strictly speaking) an alien show of color as the days draw in, and I hope the sight of at least some of these will add to your delight in this autumn season, too.