The woodlands on the valley slopes contain many native deciduous trees, which are just starting to change color. From high above most of the trees can be readily identified by their distinctive hues. The ubiquitous oaks, for example, show up as yellowish with a slight orange tinge; while the maples are already displaying a promise of deep scarlets to come.The keyaki, or zelkova, are busy developing into a rusty reddish-brown.
These keyaki zelkova (Zelkova serrata) are native woodland trees that flourish from the coast well up into the mountains. They are one of the most common and well-known trees on Honshu, Shikoku and Kyushu, and also grow on the Korean Peninsula and the Asian mainland. In addition, keyaki are widely planted as street and park trees, and around Shinto shrines and Buddhist temples. In protected environments they live long and prosper, often growing into tall, thick specimens that are officially designated as protected natural monuments.
Keyaki are classified in the Elm Family, or Ulmaceae (nire-ka), and are sometimes confused with true elms in the genus Ulmus (nire-zoku). True elms, however, reproduce by distinctive wafer-like fruits called samara, which consist of hard, flat seeds surrounded by paper-thin membranes that help them disperse on the autumn winds. The keyaki seeds, however, are tiny (about 2 to 3 millimeters in diameter), very hard and nearly round. Also, the rock-hard seeds offer no soft nutritious flesh to attract birds and other animals that might carry them around. By themselves they would just fall to the ground underneath the parent tree and lay there.
But the keyaki have a neat trick up their sleeves. The seeds form in the leaf joints on special twigs that drop off as a single piece. The leaves on these twigs are much smaller than the regular branch leaves, but when dry are more than enough to act as sails and catch the wind. On a strong breeze the whole twig, often with up to six seeds attached, goes sailing for kilometers across farms and fields.
Most Japanese identify the local keyaki by their unique shape. The main trunk is usually very short, but divides into numerous branches that rise into the air at a steep angle, producing a silhouette that resembles an inverted witch’s broom. This shape makes the keyaki especially useful for planting along narrow streets where there is little room for trees to spread their branches out to the side.
The keyaki bark is thin, and in young trees an unattractive gray. As the tree ages, however, the bark begins to fall off in palm-size flakes. The new bark that grows in the flake scars is usually silver, giving the trunk a beautiful sheen that can noticed from a great distance. The thin leaves are shaped like a spear-point, with sharp teeth along the edges, and are attached to the branch in an alternate (noticeable gap between leaves on the right and left sides) pattern. Keyaki wood is hard, durable, with attractive grain, and dries true without twisting or warping. Many of Japans superb lacquerware crafts are made by lacquering urushi (a sumac tree) sap onto keyaki bases. The wood is also excellent for carving. My favorite keyaki product is the big usu mortars used for pounding sticky rice into mochi paste.
Be careful not to mix the keyaki up with the mukunoki (Aphananthe aspera), a similar looking woodland tree also in the Elm Family. The mukunoki tends to spread out wider, and the trunks of older trees are usually buttressed at the base. Keyaki and mukunoki leaves look identical at first, but can readily be told apart by the shape of the edge teeth and also by the pattern of side veins. Mukunoki fruits are soft, berrylike, and tart and delicious when ripened into a deep blue-black color. These trees are very common in native woodlands, but are not nearly as popular as keyaki for street or park planting.
Source: Excerpted from “A view from my veranda over keyaki zelkova and mukunoki trees” by Kevin Short
(Yomiuri Shimbun Nov. 20, 2009)
NATURE IN JAPAN 