Oaks are strong trees, most are deciduous but some are evergreen, they produce very characteristic fruits (acorns). There are several hundred oak species which grow in Europe, North Africa, Southwest Asia, Central and North America. The European Oak (Quercus robur) and the American White Oak (Quercus alba) are quite similar in appearance and characteristics. Both are deciduous and frost hardy. Mature trees can become up to 40 meters (130ft) tall and 800 years old. The mighty trunks can reach a diameter of 120 cm (4ft). Oak wood is used for the construction of buildings, ships, tools and furniture since ancient times. Many wild animals eat the acorns. The heavy branches of the trees bend outwards and develop a characteristic zigzagging line. The crown gets wide in old age. The lobed leaves are 10 - 20 cm (6 inch) long, dark green and turn yellow and brown in autumn. Many southern and Mediterranean oaks are evergreen and not frost hardy, some are smaller trees or even shrubs. Oaks are very well suited for bonsai and easy to care for, but even the frost tolerant species need winter protection when they are planted in containers.