Acer pseudoplatanus
Acer pseudoplatanus, known as the sycamore in the British Isles and as the sycamore maple in the United States, is a species of maple native to Central Europe and Western Asia. It is a large deciduous, broad-leaved tree, tolerant of wind and coastal exposure.
Although native to an area ranging from France eastward to Ukraine, northern Turkey and the Caucasus, and southward to the mountains of Italy and northern Iberia, the sycamore establishes itself easily from seed and was introduced to the British Isles by 1500. It is now naturalised there and in other parts of Europe, North America, Australia and New Zealand, where it may become an invasive species.
The sycamore can grow to a height of about and the branches form a broad, rounded crown. The bark is grey, smooth when young and later flaking in irregular patches. The leaves grow on long leafstalks and are large and palmate, with five large radiating lobes. The flowers are greenish-yellow and hang in dangling flowerheads called panicles. They produce copious amounts of pollen and nectar that are attractive to insects. The winged seeds or samaras are borne in pairs and twirl to the ground when ripe. They germinate freely in the following spring.
In its native range, the sycamore is associated with a biodiverse range of invertebrates and fungi, but these are not always present in areas to which it has been introduced. It is sometimes planted in urban areas for its value as an ornamental. It produces a hard-wearing, creamy-white close-grained timber that is used for making musical instruments, furniture, joinery, wood flooring and kitchen utensils. It also makes good firewood. The rising sap in spring has been used to extract sugar and make alcoholic and non-alcoholic drinks, and can be processed into a syrup similar to that of the sugar maple. Bees often collect the nectar to make honey.
Taxonomy and etymology
Acer pseudoplatanus was first described by the Swedish naturalist Carl Linnaeus in his Species Plantarum in 1753. It is the type species in the maple genus Acer, which is in the soapberry family Sapindaceae. Many forms and varieties have been proposed, including natural varieties such as var. macrocarpum Spach, var. microcarpum Spach, and var. tomentosum Tausch, and forms such as f. erythrocarpum Pax, f. purpureum Rehder, and f. variegatum Rehder. These are all now considered to be synonyms of Acer pseudoplatanus L.The specific name pseudoplatanus refers to the superficial similarity of the leaves and bark of the sycamore to those of plane trees in the genus Platanus, the prefix pseudo- meaning "false". However, the two genera are in different families that are only distantly related. Acer and Platanus differ in the position in which leaves are attached to the stem and in their fruit, which are spherical clusters in Platanus and paired samaras in Acer.
The common name "sycamore" was originally applied to the fig species Ficus sycomorus, the sycamore or sycomore referred to in the Bible, that is native to Africa and Southwest Asia. Other common names for the tree include false plane-tree, great maple, Scottish maple, mount maple, mock-plane, or Celtic maple.
Description
The sycamore is a large, broad-leaved deciduous tree that reaches tall at maturity, the branches forming a broad, domed crown. The bark of young trees is smooth and grey but becomes rougher with age and breaks up into scales, exposing the pale-brown-to-pinkish inner bark.The buds are produced in opposite pairs, ovoid and pointed, with the bud scales green, edged in dark brown and with dark brown tips,. When the leaves are shed they leave horseshoe-shaped marks called leaf scars on the stem. The leaves are opposite, large, long and broad, palmate with 5 pointed lobes that are coarsely toothed or serrated. They have a leathery texture with thick veins protruding on the underside. They are dark green in colour with a paler underside. Some cultivars have purple-tinged or yellowish leaves. The leaf stalk or petiole is long, is often tinged red with no stipules or leaf-like structures at the base.
The functionally monoecious or dioecious yellow-green flowers are produced after the leaves in early summer, in May or June in the British Isles, on pendulous panicles long with about 60–100 flowers on each stalk. The fruits are paired winged seeds or samaras, the seeds in diameter, each with a wing long developed as an extension of the ovary wall. The wings are held at about right angles to each other, distinguishing them from those of A. platanoides and A. campestre, in which the wings are almost opposite, and from those of A. saccharum, in which they are almost parallel. When shed, the wing of the samara catches the wind and rotates the fruit as it falls, slowing its descent and enabling the wind to disperse it further from the parent tree. The seeds are mature in autumn about four months after pollination.
The sycamore is tetraploid, whereas A. campestre and A. platanoides are diploid.
Botany
Sycamore trees produce their flowers in hanging branched clusters known as panicles that contain a variety of different flower types. Most are morphologically bisexual, with both male and female organs, but function as if they were unisexual. Some are both morphologically and functionally male, others morphologically bisexual but function as males, and still others are morphologically bisexual but function as females. All of the flower types can produce pollen, but the pollen from functionally female flowers does not germinate. All flowers produce nectar, the functionally female flowers producing it in greater volume and with a higher sugar content.Sycamore trees are very variable across their wide range and have strategies to prevent self-pollination, which is undesirable because it limits the genetic variation of the progeny and may depress their vigour. Most inflorescences are formed of a mixture of functionally male and functionally female flowers. On any one tree, one or other of these flower types opens first and the other type opens later. Some trees may be male-starters in one year and female-starters in another. The change from one sex to the other may take place on different dates in different parts of the crown, and different trees in any one population may come into bloom over the course of several weeks, so that cross-pollination is encouraged, although self-pollination may not be completely prevented.
The sycamore may hybridise with other species in Acer section Acer, including with A. heldreichii where their natural ranges overlap and with A. velutinum. Intersectional hybrids with A. griseum are also known, in which the basal lobes of the leaf are reduced in size, making the leaves appear almost three-lobed.
Distribution
The sycamore is native to central and eastern Europe and western Asia. Its natural range includes Albania, Austria, Belgium, Bulgaria, Czech Republic, France, Georgia, Germany, Greece, Hungary, Italy, Lithuania, Netherlands, Poland, Portugal, Romania, southern Russia, Spain, Switzerland, East Thrace and the former Yugoslavia. Reports of it occurring in eastern Turkey have been found to refer to A. heldreichii subsp. trautvetteri.It was probably introduced into Britain in the Tudor period by 1500 and was first recorded in the wild in 1632 in Kent. The date of its first introduction into Ireland is unclear, but the oldest specimen in Ireland is in County Cavan and dates from the seventeenth century. It was introduced into Sweden around 1770 with seeds obtained from Holland.
The lack of old native names for it has been used to demonstrate its absence in Britain before introduction in around 1487, but this is challenged by the presence of an old Scottish Gaelic name for the tree, fior chrann which suggests a longer presence in Scotland at least as far back as the Gaelic settlement at Dál Riata in the late 6th and early 7th centuries. This would make it either an archaeophyte or perhaps native if it can be seen to have reached Scotland without human intervention. At the moment it is usually classified as a neophyte, a plant that is naturalised but arrived with humans on or after the year 1500. Today, the sycamore is present in 3,461 of hectads in Britain, more than any native tree species.
The sycamore has been introduced to suitable locations outside Europe as an attractive tree for park, street or garden. These include the United States, Canada, Australia, Chile and New Zealand, Patagonia and the laurel forests of Madeira and the Azores. At the time of its introduction it was probably not appreciated that its prolific production of seeds might one day cause a problem to the landscape as it spread and out-competed native species. The tree is now considered to be an environmental weed in some parts of Australia and also Mount Macedon, near Daylesford, parts of the Dandenong Ranges, where it is naturalised in the eucalypt forests. The sycamore is also scattered in north-eastern Tasmania and also at Taroona, near the Derwent River, in southern Hobart. It is considered to be an invasive species in New Zealand, Norway, and environmentally sensitive locations in the United Kingdom.
In about 1870, the sycamore was introduced into the United States, and was planted in New York state and New Jersey. It was later cultivated as a park or street tree in New England and the Mid-Atlantic states. By the early part of the 21st century, it was naturalised in fourteen states, and in the Canadian provinces of British Columbia, New Brunswick, Nova Scotia and Ontario. The United States Department of Agriculture considers it an invasive species.