THE PLANE TREE FAMILY (Platanaceae)

This family consists of only a single surviving genus Platanus, with seven accepted species of the more than 40 described. The plants are tall trees, native to temperate and subtropical regions of the Northern Hemisphere. The hybrid ‘London plane’ is widely planted in cities worldwide. It survives well, resisting air pollutants and contributing significantly to the improvement of air quality, giving shade and aesthetically enhancing our urban environments.

The leaves are simple with palmate veins and lobes with a toothed margin, similar to those of sycamores and maples. The base of the leaf stalk (petiole) is enlarged and completely wraps around the young stem bud in its axil. The axillary bud is exposed only after the leaf falls off. The mature bark peels off or exfoliates regularly in patches, producing a typical mottled, green and white scaly appearance. On old trunks, bark may not flake off, but thickens and cracks instead. Young leaves, bark and flowers are covered with woolly hairs that fall during the growing season and may cause allergic reactions in sensitive persons.

The flowers are reduced and are borne in balls (globose heads); 3–7 hairy sepals may be fused at the base, and the petals are 3–7 and are spatulate. Male and female flowers are separate, but borne on the same plant (monoecious). The number of heads in one cluster (inflorescence) is indicative of the species. The male flower has 3–8 stamens; the female has a superior ovary with 3–7 carpels. Plane trees are wind-pollinated. Male flower-heads fall off after shedding their pollen. After being pollinated, the female flowers develop achenes (dry fruit containing a single seed) that form an aggregate ball. Typically, the ball is 2.5 - 4 cm in diameter and contains several hundred conical achenes. There is also a tuft of many thin stiff yellow-green bristle fibers attached to the base of each achene that helps in wind dispersion of the fruits as in the dandelion.

(source: Wikipedia)