I have always been interested in the natural origins of plants. Where does a particular plant come from? How and when did it come to this country? Geographic botany investigates the distribution of plants around the world.

The purple catchfly (Silene armenia), an alien to Japan

You don't have to be a specialist to enjoy investigating, though; all you need are a guidebook, a notebook and a couple of pencils. Many libraries in Japan have a good collection of wildflower guides; children's nature guides are especially easy to read and have excellent illustrations. Take a pencil and notebook along when you go for a walk in a park or along a river and use them to take notes and sketch the plants you see. Special points to watch for:

* The leaf shape. Some leaves are simple in shape, while others are divided in lobes (compound leaves). A hosta leaf is a simple leaf, whereas the cloverleaf is a compound leaf.

* The shape of the stem. Some have a circular section, such as the kudzu (Pueraria lobata), while others, such as mint, have a square section.

* The size, shape and color of the flower. Note the number of petals and the calyx. Similar flowers may bloom at different times of the year, so noting the date is useful too.

The golden-yellow Coreopsis lanceolata

Many people in Japan do not have time or space for a garden, but it is still fun to examine plants growing along the roadside or on some neglected piece of ground. On the hills above the town where I live, an old quarry was turned into a large-scale condominium complex during the economic bubble years. On the slopes around it some interesting alien plants have taken up residence for free.

Since Japan was reopened to the outside world, near the end of the Edo Period, many foreign plants have been introduced here. Some liked the new environment so much that they soon naturalized.

Some aliens stick out like sore thumbs, like the goldenrod (seitaka awadachi-so, Solidago canadensis var. scabra). Its gaudy yellow flowers bloom in September, on stems up to 2 meters tall, on waste ground all over Japan.

Other aliens require up-close examination to confirm the country of origin.

Around this time of year the yellow flowers of coreopsis (okinkei-giku, Coreopsis lanceolata) can be seen on sunny slopes. The genus coreopsis is distributed through tropical Africa, Hawaii and North America and contains some 50 species. C. lanceolata is a North American escapee. The genus name is of Greek origin; koris means "bug" and opsis means "like, resembling." The seed or cypsela of a coreopsis looks like a bug or tick. (Cypsela is a technical word for seeds which remain joined, or adnate, to the calyx.)

Last year there was an article in a Japanese newspaper complaining that this plant is starting to take over. Unlike the goldenrod, though, the coreopsis is only locally abundant, and the pretty flowers cause no harm.

Catchfly (mushitoriko, Silene armenia), or none-so-pretty, is a commonly seen alien, originally brought to Japan from Europe sometime in the Edo Period and grown as a garden ornamental. Catchfly belongs to the carnation family, the Caryophyllaceae, which includes an estimated 80 genera and some 2,000 species, concentrated in the Mediterranean region.

Plants in the carnation family always have opposite leaves, simple and without teeth on the margin. The stem nodes are slightly swollen. The flowers are bisexual and the petiole is often fringed or notched at the top.

Catchfly is an annual or biennial plant. Its stems are normally unbranched and grow to 30-60 cm high. The leaves are ovate, 3-5 cm long, and glaucous, which means they have a greenish bloom that can be rubbed off with the fingers.

Catchfly's flowers are red, light red or sometimes white, and are borne in corymbs at the tips of the stems. Each flower is about 1 cm wide and has 5 petals; the tip of each petal is slightly lobed. Just below the petals there is a small sticky band. Flies and other tiny insects that land here get stuck and cannot fly away. Catchfly is not an insect-eating plant, but the sticky band may be to protect the delicate petals from being eaten.

Dandelions are found the world over, and there are estimated to be 400 species of these sun-loving perennials. In Japan alone there are approximately 20 species. Children love to pick the ripe seed heads and blow on them, sending the seed floating away on their tiny feathery parachutes.

The European dandelion (Seiyo tanpopo, Taraxacum officinale) was introduced in the Meiji Era (1868-1912). It has now spread all over Japan, and can be seen in all urban areas. One of the main reasons this plant can reproduce so fast is its long flowering season. Native Japanese dandelions usually bloom from March until May, but their European cousin blooms straight through to September. Moreover, the European dandelion can fertilize its own flowers and set seed all by itself, while the less adaptive Japanese dandelions rely on visiting insects to cross-pollinate them. Consequently, the native species are decreasing at an alarming rate.

To tell them apart, inspect the flower. The European dandelion is slightly larger, up to 5 cm across, a full centimeter broader than the native Kanto tanpopo (T. platycarpum). Then note the green, leaflike bracts beneath the flower head: the bracts of the Kanto tanpopo all hug the base of the flower tightly, but some of the bracts of the European dandelion hang raffishly downward.

The English name dandelion actually comes from Old French dent de lion (tooth of the lion), referring to the jagged edges of the leaves. The generic name taraxacum is more obscure. Two different Greek etymologies have been suggested. One combines taraxis, referring to "eye disorders" and akeomai, "to cure"; the herb is traditionally a specific against eye disorders. The second suggestion is taraxo, "I have caused," and achos, "pain," alluding to the medical efficacy of the plant.

In fact dandelion is rich in protein, sugar, vitamins and minerals. It is a diuretic, a mild laxative, a tonic, a blood purifier and an aid to digestion. All parts of the plant are edible and beneficial to health. The root can be roasted and ground to make a substitute for coffee, while the young green leaves make a tasty addition to a salad.