Tree spotlight no:8 – Plane Tree

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2033 year old Plan Tree in Azerbaijan

Platanus is a genus consisting of a small number of tree species native to the Northern Hemisphere. They are the sole living members of the family Platanaceae. All members of Plantus are tall, reaching 30–50 m (98–164 ft) in height. All except for P. Kerrii are deciduous, and 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.

They are often known in English as planes or plane trees. Some North American species are called Sycamores (especially Platanus Occidentalis), although the term sycamore also refers to the Ficus Sycomorus, the plant originally so named, and to the Sycamore maple Acer Pseudoplatanus.

london plane leaves and fruit.job

Botany:

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 (see table below). 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 achenes that form an aggregate ball. Typically, the core of the ball is 1 cm in diameter and is covered with a net of mesh 1 mm, which can be peeled off. The ball is 2.5–4 cm in diameter and contains several hundred achenes, each of which has a single seed and is conical, with the point attached downward to the net at the surface of the ball. There is also a tuft of many thin stiff yellow-green bristle fibers attached to the base of each achene. These bristles help in wind dispersion of the fruits as in the dandelion.

plane tree seed head

The leaves are simple and alternate. The mature bark peels off or exfoliates easily in irregularly shaped patches, producing a mottled, scaly appearance. On old trunks, bark may not flake off, but thickens and cracks instead.

Uses

The principal use of these trees is as ornamental trees, especially in urban areas and by roadsides. The London plane is particularly popular for this purpose. The American plane is cultivated sometimes for timber and investigations have been made into its use as a biomass crop. The oriental plane is widely used as an ornamental and also has a number of minor medicinal uses.

Cultural history

Most significant aspects of cultural history apply to Platanus orientalis in the Old World. The tree is an important part of the literary scenery of Plato’s dialogue Phaedrus. Because of Plato, the tree also played an important role in the scenery of Cicero’s De Oratore.

Champion Trees of Ireland

Champion Trees - a selection of Ireland's Great Trees- the tree council of Ireland

Two of the trees from Trinity College Dublin feature in this beautifully illustrated book Champion Trees, a selection of Ireland’s great trees.

Platanus orientalis (Oriental Plane Tree), Trinity College Dublin – 4.98 x 11.5 meters.

Acer macrophyllum (Oregon Maple Tree), Trinity College Dublin – 3.68 @ 1.05 x 16 meters – 2nd greatest girthed of its kind in Ireland.

Of note is that the two Oregon Maples in the main square are also thought to be the oldest trees on the Trinity College Dublin campus.

Science Notes: Plane Tree Nodules

The nodules on the plane trees give them an unusual knobbly shape. They are also unusual when viewed at high magnification in the scanning electron microscope. This SEM photo shows a rather messy, chaotic structure…

Plane Tree Nodules fig1 …which is very different from that of normal wood. For example here’s a picture Clodagh took of a twig from the Oregon maple, at the same magnification:

 Plane Tree Nodules fig2 This remarkably regular pattern of cells makes the wood very strong and light. The nodule is also made of cells, but they have grown in a chaotic, random pattern, creating material which is much weaker. This explains why these trees have made very thick trunks to support their weight. Nodular wood is much sought-after by woodturners because it makes a beautiful patterned surface when made into, for example, a bowl, but they know to treat it very carefully because it breaks easily.

Not all the wood in the plane trees is chaotic though. Clodagh found this area where the tree has managed to get back to something approaching a regular cellular structure:

Plane Tree Nodules fig3

David