Ferns are very old plants that long predate the dinosaurs and were already abundant during the Carboniferous Period 350 million years ago, when many species grew in treelike form. Nowadays, they are perfect for bringing a natural feeling to gardens, and complementing trees and shrubs.

Though they are primarily shade lovers, ferns have a wide range of chracteristics -- from the delicate and intricate foliage of some species to the tough leathery leaves of others. This, and the fact that they come in both deciduous and evergreen forms, allows them to grow in a variety of situations, from woods and fields to marshes, mountains and cliffs.

Mostly terrestrial, some ferns will even grow in direct sunlight, while others clamber over rocks and some of them scale tree trunks. However, there are also aquatic ferns such as o-aka-uki-kusa (water fern; Azolla japonica), which grows in ponds and paddy fields in Honshu, Kyushu and Shikoku.

Throughout Japan, though, there are hundreds of native species, and from early times, some of them have been cultivated in gardens. In turn, Japanese ferns are now often grown in European and American gardens.

Long ago, people were baffled about how ferns reproduced without bearing any flowers, and it was only with the invention of microscopes that the mystery began to be understood. After close study, it was realized that ferns produce microscopic, dustlike spores (sporangium) by the million. Each of the spores is a single-celled organism, and when spores released from ferns drop to the ground, or are dispersed far away by the wind, they go through a two-stage life cycle before becoming true ferns.

Needing light and water, the spores at first start to grow by cell-division until tiny, green, flattened, heart-shaped plants known as prothallus are formed. These tiny plants attach themselves to the soil by rhizoids, which are single-celled, hairlike structures serving as roots that help to anchor the plants to the ground and search for moisture and nutrients.

The underside of the prothallus bears both antheridia (male) and archegonia (female) reproductive organs. With the aid of moisture, motile male sperm cells (spermatozoids) swim to the antheridia to fertilize the egg cell. Fertilized cells divide numerous times to form sporophytes, which develop tiny unfernlike leaves before, finally, true fern leaves develop.

Despite such a seemingly complex reproductive cycle, ferns -- together with horsetails and clubmosses -- comprise an ancient division of plants known as Pteridophyta. Today, they are widely distributed around the world, with the greatest concentration in the tropics.

Technical terms used to describe ferns differ from those used to describe flowering plants. Their leaves, for example, are called fronds, while their stems are known as rhizomes. These unique aspects make them fascinating to observe and study, and whenever you are out for a walk in your local park or in the countryside, it can be interesting to take note of the varieties you come across. Woods are ideal places to see where ferns grow, before the leaf canopy unfolds. Then, during summer, it is interesting to examine the same area again to see how much shade they can tolerate.

The first Japanese fern I really took note of was the mamezuta (Lemmaphyllum microphyllum). This is an evergreen that creeps over rocks and up tree trunks and is known as an epiphyte, meaning a plant that uses another plant or structure for support, though not being parasitic and taking no nourishment.

Fronds on the mamezuta are orbicular to elliptic, 1-2 cm long and 6-15 mm wide. There are no teeth on the margin of the fronds, which are leathery with shiny upper surfaces and light-brown sporangium on the undersides of fertile ones. Mamezuta can be seen growing on hills and low mountains throughout Honshu.

Another epiphytic fern is the hitotsuba (Pyrrosia lingua), known as the Japanese felt fern, tongue fern or creeping fern. This evergreen is often seen in traditional Japanese gardens, with its leaves looking like green tongues 10-27 cm long.

Beni-shida (Dryopteris erythrosora), also known as Japanese red shield fern or autumn fern, and oni-yabu-sotetsu (Crytomium fortunei), also known as Japanese holly fern, are two evergreens that will tolerate a wide range of sites, from sun to light shade. The Japanese shield fern, in particular, is a beautiful variety with delicately pinnate, 30-70 cm fronds that is often cultivated in the United States. Growing best in moist, well-drained and fertile soil, its young fronds are reddish, hence the common name.

The fronds on the holly fern are 30-60 cm long, pinnate and leathery, with glossy upper surfaces. Holly ferns are often seen growing on old walls in gardens.

Perhaps one of the most cosmopolitan ferns, though, is oba-no-i-no-moto-so (Pteris cretica; brake fern). This species' native range extends right across the tropics and the warm temperate regions of the northern hemisphere, and along the way it has collected other popular names, including the warm fern, stove fern and Old World fern. However, the fern's species-name, Pteris cretica, alludes to the Mediterranean island of Crete where it also grows, and the generic name pteris is also of Greek origin, meaning fern.

Pteris is an evergreen with 1-5 pairs of simple or forked, thin pinnate fronds that are 20-40 cm long and leathery with tiny awn-shaped teeth on the margins. Cultivate by growing in semi-shade in soil with good drainage.

One of my personal favorites is urajiro (Gleichenia japonica), a tall evergreen brackenlike fern that grows on dry poor soil in lightly shaded woodlands and spreads by creeping rhizomes. It is native to western Honshu, Okinawa, China and Southeast Asia, extending all the way down to Australia. This magnificent fern's fronds can be 50-100 cm long and are pinnate, with white undersides.

Unfortunately, this fern is not easy to cultivate, but it is worth trying. Recently, I managed to move some urajiro from a shaded bank that was about to be flattened by earthmovers to large pots filled with akadama, the popular, reddish horticultural soil. Right now, I'm hoping for the best.

So, next time you're out strolling, keep your eyes peeled for ferns. Equip yourself with a pocket-sized reference book, and you'll then be able to learn more fascinating facts about these ancient plants.