Japan's national government has never formally named a "national flower", as with other symbols such as the green pheasant, which was named as national bird (by a non-government body) in 1947, but it wasn't until 1999 that the national flag and national anthem were officially passed into law.
A de facto national flower for Japan for many is the sakura or cherry blossom, while a stylised picture of a chrysanthemum is used as the official seal of the Japanese Imperial Family.
A cherry blossom is the flower of any of several trees of genus Prunus, particularly the Japanese Cherry, Prunus serrulata, which is sometimes called sakura after the Japanese (桜 or 櫻; さくら). Many of the varieties that have been cultivated for ornamental use do not produce fruit. Edible cherries generally come from cultivars of the related species Prunus avium and Prunus cerasus.
In Japan cherry blossoms also symbolize clouds due to their nature of blooming en masse, besides being an enduring metaphor for the ephemeral nature of life, an aspect of Japanese cultural tradition that is often associated with Buddhistic influence, and which is embodied in the concept of mono no aware. The association of the cherry blossom with mono no aware dates back to 18th-century scholar Motoori Norinaga. The transience of the blossoms, the extreme beauty and quick death, has often been associated with mortality; for this reason, cherry blossoms are richly symbolic, and have been utilized often in Japanese art, manga, anime, and film, as well as at musical performances for ambient effect. There is at least one popular folk song, originally meant for the shakuhachi (bamboo flute), titled "Sakura", and several pop songs. The flower is also represented on all manner of consumer goods in Japan, including kimono, stationery, and dishware.
The Sakurakai or Cherry Blossom Society was the name chosen by young officers within the Imperial Japanese Army in September 1930 for their secret society established with the goal of reorganizing the state along totalitarian militaristic lines, via a military coup d'état if necessary.
During World War II, the cherry blossom was used to motivate the Japanese people, to stoke nationalism and militarism among the populace. Even prior to the war, they were used in propaganda to inspire "Japanese spirit," as in the "Song of Young Japan," exulting in "warriors" who were "ready like the myriad cherry blossoms to scatter." In 1932, Akiko Yosano's poetry urged Japanese soldiers to endure sufferings in China and compared the dead soldiers to cherry blossoms. Arguments that the plans for the Battle of Leyte Gulf, involving all Japanese ships, would expose Japan to serious danger if they failed, were countered with the plea that the Navy be permitted to "bloom as flowers of death." The last message of the forces on Peleliu was "Sakura, Sakura" — cherry blossoms.
Japanese pilots would paint them on the sides of their planes before embarking on a suicide mission, or even take branches of the trees with them on their missions. A cherry blossom painted on the side of the bomber symbolized the intensity and ephemerality of life; in this way, the aesthetic association was altered such that falling cherry petals came to represent the sacrifice of youth in suicide missions to honor the emperor. The first kamikaze unit had a subunit called Yamazakura or wild cherry blossom. The government even encouraged the people to believe that the souls of downed warriors were reincarnated in the blossoms. In its colonial enterprises, imperial Japan often planted cherry trees as a means of "claiming occupied territory as Japanese space".
The most popular variety of cherry blossom in Japan is the Somei Yoshino. Its flowers are nearly pure white, tinged with the palest pink, especially near the stem. They bloom and usually fall within a week, before the leaves come out. Therefore, the trees look nearly white from top to bottom. The variety takes its name from the village of Somei (now part of Toshima in Tokyo). It was developed in the mid- to late-19th century at the end of the Edo period and the beginning of the Meiji period. The Somei Yoshino is so widely associated with cherry blossoms that jidaigeki and other works of fiction often depict the variety in the Edo period or earlier; such depictions are anachronisms.
Winter sakura (fuyuzakura/Prunus subhirtella autumnalis) begins to bloom in the fall and continues blooming sporadically throughout the winter. It is said to be a cross between Tokyo Higan cherry (edohiganzakura/P. incisa) and Mamezakura/P. pendula.
Other categories include yamazakura, yaezakura, and shidarezakura. The yaezakura have large flowers, thick with rich pink petals. The shidarezakura, or weeping cherry, has branches that fall like those of a weeping willow, bearing cascades of pink flowers.
Japan gave 3,020 cherry blossom trees as a gift to the United States in 1912 to celebrate the nations' then-growing friendship, replacing an earlier gift of 2000 trees which had to be destroyed due to disease in 1910. These trees were planted in Sakura Park in Manhattan and famously line the shore of the Tidal Basin in Washington, D.C. The gift was renewed with another 3,800 trees in 1965. The cherry blossom trees continue to be a popular tourist attraction (and the subject of the annual National Cherry Blossom Festival) when they reach full bloom in early spring. Also, Balboa Park of San Diego has 2,000 cherry blossom trees that blossom in mid to late March. In Los Angeles, over 2,000 trees are located at Lake Balboa in Van Nuys.
These trees were donated by an anonymous Japanese benefactor and were planted in 1992. They originated from a single parent tree and were developed to grow in warm climates. Philadelphia is also home to over 2000 flowering Japanese cherry trees, half of which were a gift from the Japanese government in 1926 in honor of the 150th anniversary of American independence, with the other half planted by the Japan America Society of Greater Philadelphia between 1998 and 2007. Philadelphia's cherry blossoms are located within Fairmount Park, and the annual Subaru Cherry Blossom Festival of Greater Philadelphia celebrates the blooming trees. The University of Washington in Seattle also has cherry blossoms in its Quad.
Other US cities have an annual Cherry Blossom Festival (or Sakura Matsuri), including the International Cherry Blossom Festival in Macon, Georgia, which features over 300,000 cherry trees. Belleville, Bloomfield, and Newark, New Jersey celebrate the annual Branch Brook Park Cherry Blossom Festival in April, which attracts thousands of visitors from the local area, Japan, and India. As of April 2009, Branch Brook Park has a cherry tree collection with over 4,000 cherry blossoms in more than fourteen different varieties. Branch Brook Park will soon have more flowering cherry trees than Washington, D.C., thanks to an ongoing replanting program. The Brooklyn Botanic Garden in New York City also has a large, well-attended festival. Portsmouth, New Hampshire, is the site of the peace conference that produced the Treaty of Portsmouth, for which the original Washington, DC cherry trees were given in thanks. Several cherry trees planted on the bank of the tidal pond next to Portsmouth City Hall were the gift of Portsmouth's Japanese sister city of Nichinan - the hometown of Marquis Komura Jutarō, Japan's representative at the conference.
· The blossoms are pickled in salt and Umezu (Ume vinegar), and is used for coaxing out flavor in Wagashi, (a traditional Japanese confectionery,) or Anpan, (a Japanese sweet bun, most-commonly filled with red bean paste.)
· Salt-pickled blossoms in hot water is called Sakurayu, and is drunk at festive events like weddings in place of Green tea.
· The leaves, mostly from the Ōshima cherry because of the softness, are also pickled in salted water and used for Sakuramochi.
Since the leaves contain Coumarin, however, it is not recommended that one eats them in great quantities, due to its toxicity.
Source, Images: http://en.wikipedia.org/wiki/Sakura