Blue Japanese oak (Quercus glauca Thunb.) is a medium-sized tree native of Asia used as fodder in Nepal and India.
Blue Japanese oak is an evergreen tree, 10 to 20 m high in its native Asia and slightly smaller (8-10 m) under Mediterranean conditions. It has a straight cylindrical bole, up to 45 cm in diameter, covered with greyish bark (Hélardot, 2015; Ducatillion, 2010; Orwa et al., 2009). The tree may be multi-stemmed (NC State University, 2015). The crown is oval to rounded. Its branches are widely spread, and young twigs are glabrescent, thick, stiff, dark olive green with pale lenticels. Blue Japanese oak is taprooted (Hélardot, 2015; Ducatillion, 2010; Orwa et al., 2009). The leaf blades are evergreen, alternate, simple, oblong to obovate-oblong, acuminate at the apex and broadly cuneate at the base, serrated, 7-13 cm long and 4-5 cm broad. The upper face of the leaf is glabrous and glossy green and the lower face is silky and hairy, blue green in colour (Hélardot, 2015; Ducatillion, 2010; Orwa et al., 2009; Forestry Nepal, 2005). New foliage is a rich green or bronze to purple green (Forestry Nepal, 2005). Flowers are dioecious catkins. Male flowers are silky, hairy, loose drooping catkins: they bear 4 stamens. Female catkins are shorter and bear 2-4 flowers. The fruits are 1.5-2 cm long x 0.9-1.4 cm broad, ovoid acorns, generally borne in clusters (3 fruits/cluster). A third or half of the fruit is enclosed in a ringed, scally silky cup (Hélardot, 2015; Forestry Nepal, 2005).
Blue Japanese oak acorns are edible, but their high tannin content makes it necessary to leach them prior to grinding. This can be done by thorough washing of the acorns or by burying them in the ground to overwinter. However, leaching the flour may be more efficient (Orwa et al., 2009). The acorns can be dried, ground into powder and used as flour when mixed with cereals to make breads. The powder can also be used as a thickening agent in stews. Roasted seeds can be used as a coffee substitute. Leaves can be cooked and eaten as a vegetable in times of scarcity (Orwa et al., 2009). The branches and twigs are good material for culturing mushrooms (for example, Pleurotus eryngii) (Ducatillion, 2010). Blue Japanese oak is subject to galls that are sources of tannin and dye. The wood is a good quality timber, finely textured, hard and durable, and is also valuable fuelwood (Orwa et al., 2009). The tree is regarded as an ornamental plant for gardens, parks and streets because it has a good shape and provides desirable shade (Orwa et al., 2009). The leaves and stems are valuable fodder, relished by deer in the USA. The leaves are used to feed oak tasar silkworms in the hilly regions of China and India (Arindam Basu, 2015; Ducatillion, 2010).