The Japanese horse chestnut is in flower: Aesculus turbinata also とちのき (栃木･橡) see this page for good photos of various parts of the tree and fruit.
The common name horse chestnut is used for any of several trees of the Aesculus genus – there are 15 recognized species. Horse chestnuts are in an entirely different botanical family from the sweet chestnut tree, Castanea vesca. Horse chestnuts exist in nature both as a tree and a shrub and are found in all temperate regions of Asia, Europe and North America.
The name Aesculus is actually a misnomer, coming originally from the word esca, meaning food. It was applied by ancient peoples to a certain species of oak; somehow the name was transferred over the years to the horse chestnut. The name hippocastanum is thought to refer to the horse chestnut’s ability to heal horses and cattle of respiratory illnesses. Another possibility may be that it is named for the small horseshoe-like markings that are present on the branches of the horse chestnut tree. Horseshoe-shaped leaf scars are clearly visible at the base of a branch or twig; these may be the origin of the English name for the tree.
When pollinated, the flower develops into a fruit with a spiny green shell that usually contains two seeds. Mature fruit falls to the ground from September, the shell often breaking on impact.
The fruit are traditionally strung individually by English children and bashed together in the game of the same name. Whichever conker survives the collision unbroken wins, and may go on to other battles. A conker which has won once is known as a ‘one-er’, a two-time winner as a ‘two-er’ and so on. The wood of the horse chestnut is soft, and is used to make paper pulp and sometimes in carpentry. It is commonly used to make packing crates.
All the branches of the tree curve gracefully upwards in winter. In February or March, these buds open out into palmate leaves. Each leaf has five or seven leaflets with serrated edges. Weighed down by foliage, the crown of the tree gradually opens out in spring and summer. In April or May, the horse chestnut goes into bloom. Each candle-like inflorescence is made up of many four-petalled white or, in one variety, pink, flowers with a slight scent. The white variety has hints of red and yellow.
Each branch bears sticky brown buds in opposing pairs along its sides, topped off by an apical bud. The sticky sap, together with the bud scales, protects the buds from frost and insect damage.