Apple trees are generally small trees, and a given variety can be grafted onto dwarfing or semi-dwarfing rootstocks for smaller and less vigorous plants. If left untrimmed, a tree grown with standard (seedling) rootstock will often reach a height of 9 metres (30 feet) with an equally large crown diametre. The bark is usually brown and scaly. The simple leaves are roughly oval in shape and usually have fine teeth along the margins. Apple flowers are showy with five white petals, often tinged with pink, and numerous stamens. The flowers are pollinated by bees and other insects, and most varieties require cross-pollination for fertilization