Platanus (Genus) Plane trees
Common names: Planes or plane trees (English), Sycamores (Some North American species
Platanus is a genus comprising a number of tall (30–50m) dicotyledon tree species native to the Northern Hemisphere. They are the sole living members of the family Platanaceae. There are about 10 species. Platanus kerrii is the only tropical species and the only one that is deciduous. Platanus orientalis is found from western Asia and southern Europe. Several others, including Platanus occidentalis, Platanus racemosa, Platanus wrightii, Platanus lindeniana and perhaps others are from North America. Most are found in riparian or other wetland habitats in the wild, though proving drought-tolerant in cultivation. The hybrid London Plane has proved particularly tolerant of urban conditions.
Platanus leaves are simple, large, broad, palmate shaped leaves with a leaf blade length of 120–250 mm and a leaf blade width of 100–240 mm and are borne alternately on the stem. 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 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 become an achene (small dry indehiscent (remaining closed at maturity) one-seeded fruit), which united with the others on the flower-head to form the spherical fruit up to 4cm in diameter. These fruits ripen to a brown colour and persisting into winter, usually borne in pairs, hanging from long, thin stalks.
There is a tuft of many thin stiff yellow-green bristle fibres attached to the base of each achene. These bristles help in wind dispersion of the fruits as in the dandelion.
A common characteristic of the Platanus species is that the bark peels off easily in irregularly shaped patches, producing a mottled, scaly appearance of creamy, olive and yellow patches. This is due to a lack of flexibility in the bark which doesn't grow at the same speed as the trunk and hence exfoliates from it.
The green fruit.
"Fruits of Platanus orientalis". Licensed under Public domain via Wikimedia Commons.
Bole of an aged Platanus
The exfoliating bark.
Photo of a ripened fruit cut open to show the many achene inside.
Photo showing bristle fibres attached to the base of each achene.
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