Before the Nara period (AD 710 to 794), Yanagi (“willows”) which were called “Nagira” were planted for viewing pleasure. There was a custom to hang a prayer over branch of willow for person who goes on journey for safe traveling in Tyouan in China. From that past time, willow has had connections with human life.
A willow is a sun tree and has a stipule and short leaf stalk alternate leaf forms alignment or ovoid figure and it is a deciduous tree of varying height, the tallest of which reaches 20m.
A willow belongs to Salix genus inner of salicaceae family a part of Salicales order a portion of Magnoliopsida class. It is Magnoliophyta division part of Plantae kingdom. This plant is hermaphrodite and makes a capsule which putts a number of small seed in wool to scatter widely to use wind and have dormant buds covered with one scale which fuses into 2 scales and makes amentum a kind of indefinite inflorescence which is formed by gathering a small apetalous flower. It has male flower’s petal and female flower’s one. A male flower only has several stamen and a female flower alone has several pistil and both have small bract and secretory portion.
Mainly willow is living the temperate zone but it can live the polar region so they can live a lot of the northern hemisphere such as the mountain, the water’s edge and the tundra. A willow lives in the high mountains and in the tundra becomes lower than flatland’s one. In Japan, a lot of willows live in the mountain and the water’s edge. In Kochi, mainly they are living 2km around riverside area of upriver of the Shimantogawa bridge in Shimanto city and Kagami river accumulates silt and fine sand in Kochi city such as Salix chaenomeloides, S. gracilistyla, S. yoshinoi and S. koriyanagi.
They are 4 advantages to living by the riverside. The one is that they produce large number of seeds short time before next disturbance comes and seed is very right so it can spray more widely. The second is the seed has high germination rate so as long as there is water. The third is because seed’s early time growing is very fast, they can get enough light to grow. The fourth is they have strong vital force, for example even if they are buried by earth and sand, they can continue growing. Therefore, they can endure that difficult environment and become a dominant species in that place. But their seed can’t remain dormant and they don’t make seed banks. Moreover, good place for willow is different from species to species so chance to get good place is only once time per season of seed scatter, and various willow’s patches are formed every season by the current of river. When willow grows in the riverside, sand piles up around their roots and become a footing for other plants. Because of 4 advantages and that they like mist area and have strong roots, they are usually planted on riverside and lakeside to prevent flood damage.
Also, a willow’s constituent that is called “salicylic acid” is useful for human beings as an antipyretic-analgesic. A fact that salicylic acid is contained in branches and leafs was discovered by Hippocrates who is called the father of medical as the oldest medicine of the world. It is said he used for bark to relieve pain and alleviate of fever and leaf to ease pain for childbirth. From the above mentions, we can say we live by willow’s favor.