Platanaceae

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Platanaceae
Temporal range: Cretaceous - Recent
Inflorescence of Platanus × hispanica
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
Order: Proteales
Family: Platanaceae
T. Lestib.[1]
Genera
  • †Macginitiea (Wolfe & Wehr)* Platanus L., 1753

Platanaceae is a family of flowering plants belonging to the order proteales. It has been recognized by almost all taxonomists, and is sometimes called the "plane-tree family". The family consists of only a single extant 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.

The plane-tree is referenced in Pliny the Younger's letter to Domitius Apollinaris as part of his description of his Tuscan Villa located somewhere in Tuscany in the 1st Century.

49 mya Fossil Macginitiea gracilis from the Klondike Mountain Formation, Washington

Description

Example of Platanus orientalis
  • Large, sympodial, deciduous tree, speckled bark that sheds in large irregular sheets, leaving a smooth surface that is mottled and pale, persistent bark at the base of the trunk. Indumentum with large glandular hairs, multicellular and uniserrate or short with uniserrate ramification (in candelabrum), in stellate fascicles; glandular hairs with unicellular, globular capitulum. Cuticular waxes without crystalloids, with rods and plates.
  • Leaves generally with very variable shapes and nervation, simple, alternate, more or less distichous, isobilateral palmate with 3-7 lobes (palmatifid to palmatisect) with whole edges or with glandular teeth (each one with a mid-vein that broadens towards the glandular apex, where it ends in an open hole), or penninerved and whole (Platanus kerrii), this shape is common in young, vernal leaves in other species, vernation folded, with the petiole usually sheathed, enclosing the axillary bud (the bud is free in Platanus kerrii), stipules foliose, large, intrapetiolar, tubular, normally caduceus, in Platanus kerrii scarious, small, basally fused to the petiole. Domatia present. Stomata irregularly anomocytic.
  • Stems with aggregated rays in the xylem, with nodes 7-lacunar, cork cambium present and superficial. Buds covered by a single scale.
  • Plants monocious, the flowers of each sex in separate inflorescences.
  • Inflorescences 1-7(-12) in large hanging peduncles, each one a unisexual, globular capitellum, pedunclulate or seated, with numerous flowers, derived from the condensation of a panicle, with a circular bract at the base and bracteoles among the flowers.
  • Flowers small, inconspicuous, hypogenous, regular unisexual. Receptacle short, smooth. Hypogynous disk absent. Perianth reduced. Sepals 3-4(-8), free or basally fused, shorter than the petals, triangular. Petals 3-4(-8), truncated-spatulate or vestigial, scarious, frequently absent in the female flowers. Male flowers with androecium haplostemonous, isostemonous, oppositisepal, with 3-4(-8) stamens, gynostemium short or vestigial, anthers basifixed, not versatile, dithecous, tetrasporangiate, elongated, connectivum apically widened, peltate, dehiscence along longitudinal valves; pistillidium sometimes present. Female flowers with superior gynoecium of (3-)5-8(-9) carpels apocarpous in 2-3 whorls, imperfectly closed apically, surrounded by large petals, linear stylodious, stigmas internal, decurrent in two ridges, more or less dry, two ovules per carpel but one nearly always aborts, orthotropous, bitegmic, crassinucellated, pendulous, apical to marginal placentation. Staminodes 3-4. No nectaries.
  • Fruits in achene, clavate, grouped in a globular capituliform infructescence, each fruit is surrounded by long hairs.

  • Fruiting body of Platanus orientalis (Oriental plane tree).

  • Fruiting body of American sycamore (Platanus occidentalis) with some achenes removed.

  • An achene.

  • Cross section of an achene with the seed shown in brown.

  • Seeds small with thin testa with little endosperm, oily and proteinaceous, embryo thin and straight with 2 linear cotyledons, often uneven.
  • Pollen in subprolate monads, 16-22 μm in length, tricolpate, sometimes 6-rugate, tectate-columellate, reticulated surface, the base layer as thick as the tectum.
  • Chromosomal number: 2n = 14, 16, 21, 42; x probably equal to 7 or 8.

Ecology

Pollination is anemophilous. Flowering begins at the start of spring when the new leaves are sprouting.

The heads that sustain the fruit normally shed the year after they have matured, during the autumn. Dispersion of the individual fruiting bodies, with their thistledown, is anemocorous (they are sometimes dispersed by water as a secondary mechanism).

The plants grow in cool situations in temperate climates and are frequently found on the banks of rivers and streams. They are totally absent from dry or excessively cold areas.

Phytochemistry

They contain cyanogenic glycosides derived from tyrosine, flavonoids belonging to the proanthocyanidins group (eg prodelphinidin) and flavonols (kaempferol, quercetin, myricetin), in addition to triterpenols (including betulinic acid). They lack ellagic acid, saponins and sapogenins.

Cultivation

Morphological details of Platanus occidentalis

The main use for a number of the species is to provide shade in pedestrian areas in temperate regions, particularly the London planetree (Platanus x hispanica), which is widely distributed throughout Europe and North America. It is highly resistant, probably due to so-called hybrid vigour, although its use requires caution due to their allergy-producing thistledown. The parent species are also grown for the same effect but with poorer results as they are less resistant to contamination, among other reasons. The wood is used in cabinetmaking, panelling and other interior work, and is also prized for its long burn time.

Fossils

A large number of fossils of this family have been recorded from the Lower Cretaceous (98-113 million years ago, Platanocarpus), the examples from that time had very small pollen (8-10 μm) and a developed perianth and they lacked hairs at the base of the nucule. It is thought to have had entomophilous pollination. During the Middle Cretaceous the fossilized forms with platanoid leaves became mixed with pinnate leaves (Sapindopsis) or pedatisect leaves (Debeya, Dewalquea), and these forms lasted until the Eocene. The leaves with typical stipules belonging to the sub-genus Platanus are very common in Palaeocene formations (60 M years ago). It is thought that the only modern genus, Platanus, is a relict that can be considered a living fossil. It must have been polyploidy, during its evolution judging by the size of its stomata.

Systematic position

The APG II system (2003; unchanged from the APG system of 1998) allows the option of including it in the family Proteaceae, or treating it as distinct as a segregate family. In as far as APG II accepts the family it is placed in the order Proteales, in the clade eudicots. This represents a slight change from the APG system, of 1998, which did accept this family. The Cronquist system of 1981 recognized the family and placed it in order Hamamelidales, in subclass Hamamelidae [sic] in class Magnoliopsida (dicotyledons). The Dahlgren system and Thorne system (1992) also recognized this family and placed it in the order Hamamelidales in superorder Rosanae in subclass Magnoliidae sensu Dahlgren and Thorne (dicotyledons). The Engler system, in its 1964 update, also recognized the family and placed it in the order Rosales in subclass Archichlamydeae of class Dicotyledoneae. The Wettstein system, last revised in 1935, also recognized the family and placed it in the order Hamamelidales in the Monochlamydeae in subclass Choripetalae of the class Dicotyledones. Based on molecular and morphological data the APW (Angiosperm Phylogeny Website) places the family in the order Proteales as a sister family to the proteaceae, making them the northern hemisphere version of this family (cf. AP-website).

Taxa included

Theoretical introduction to Taxonomy

The only genus, Platanus L., 1753, has the type species Platanus orientalis L., 1753. It is divided into two sub-genera: the sub-genus Castaneophyllum J.-F. Leroy, 1982, with elliptical, penninerved leaves with small scarious, stipules, that only includes Platanus kerrii Gagnep., 1939, an isolated relict species that represents the genus’ evolutionary basal branch and which is a sister genus and is the sister group of the other species, including the sub-genus Platanus.

Scientific name Common name Distribution Flowers Notes
Platanus acerifolia Willd.—Sp. Pl., ed. 4 [Willdenow] 4(1): 474. 1805 Maple-leaved Plane ?
Platanus algeriensis Hort. ex K.Koch—Dendrologie 2(1): 468. 1872 [dic 1872] - ?
Platanus chiapensis Chiapas Plane south east of Mexico ? Sub-genus Platanus
Platanus gentryi Nixon & J.M. Poole, 2003 Gentry’s Plane western Mexico ? Sub-genus ‘‘Platanus’’
Platanus × hispanica
(P. occidentalis × P. orientalis;
sin. P. × acerifolia, P. × hybrida) 		London Plane, Hybrid Plane Origen cultivated 1-6 Sub-genus ‘‘Platanus’’
Platanus kerrii Gagnep., 1939. Kerr’s Plane Laos, Vietnam, probably south China 10-12 Sub-genus Castaneophyllum
Platanus mexicana Moric., 1837[2] Mexican Plane north east and central Mexico 2-4 Sub-genus ‘‘Platanus’’
Platanus oaxacana Oaxaca Plane southern Mexico ? Sub-genus ‘‘Platanus’’
Platanus occidentalis L., 1753[3] American Sycamore, American Plane, Buttonwood, Occidental Plane East of North America 1-2 Sub-genus ‘‘Platanus’’
Platanus orientalis L., 1753 [4] Oriental Plane South east Europe, Near East, Iran, central Asia, Pakistan, India 3-6 Sub-genus ‘‘Platanus’’
Platanus racemosa Nutt., 1842 (= P. californica Benth., 1844) California Sycamore, Western Sycamore, Aliso California and Mexico 3-7 Sub-genus ‘‘Platanus’’
Platanus rzedowskii Nixon & J.M.Poole, 2003 Rzedowski’s Plane eastern Mexico ? Sub-genus ‘‘Platanus’’
Platanus wrightii S. Watson, 1875 Wright’s Plane Arizona Sycamore or Alamo Arizona, New Mexico, north west Mexico 2-4 Sub-genus ‘‘Platanus’’

Hybrids

Bark of Platanus orientalis

The London planetree or hybrid plane has long been considered a hybrid derived from the cross between Platanus occidentalis and Platanus orientalis, despite this its origin is not clear. Some experts think it originated in London and others in Spain or even in natural or cultivated hybrid form (or not) in Turkey. The question has not been investigated with modern molecular methods. As a consequence even its nomenclature is hotly debated, to the extent that Anglo-Saxon authors deny the priority of the name used in Spain (following Maria da Luz de Oliveira Tavares Monteiro da Rocha Afonso, 1990, see References). The plant is not found in the wild even though it appears in a naturalized form along the banks of rivers and streams.

Hybrid (?) Platanus × hispanica Mill. ex Münchh., 1770 (= P. orientalis var. acerifolia Aiton, 1789; P. hybrida Brot., 1804; P. vulgaris Spach, 1841, nom. illeg.; P. × acerifolia.

Other names proposed for hybrids that are probably synonymous with the above, which is the only name in English, and which represent smaller minorities are:

  • Hybrid Platanus × cantabrigensis A.Henry, 1919
  • Hybrid Platanus × parviloba A.Henry, 1919

Notes

The references consulted do not agree as to whether the fruit is a nucule or achene, the difference between the two ultimately depends on the size of the pericarp and the extent of its lignification. The fruit is dry, indehiscent, monocarpelar and monospermatic.

References

  1. ↑ Angiosperm Phylogeny Group (2009). "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III" (PDF). Botanical Journal of the Linnean Society 161 (2): 105–121. doi:10.1111/j.1095-8339.2009.00996.x. Retrieved 2013-07-06. 
  2. ↑ Other names: P. lindeniana M. Martens & Galeotti, 1843; P. mexicana var. peltata Jaennicke, 1899; P. chiapensis Standl., 1919; P. oaxacana Standl., 1919; P. mexicana var. interior Nixon & J.M. Poole, 2003).
  3. ↑ Other names: P. lobata Moench, 1794; P. excelsa Salisb., 1796; P. vulgaris var. angulosa Spach, 1841; P. integrifolia Hort. ex K. Koch, 1872; P. orientalis var. laciniata Kuntze, 1891; P. orientalis var. palmeri Kuntze, 1891; P. pyramidalis Hort. ex Dippel, 1893; P. glabrata Fernald, 1901; P. densicoma Dode, 1908; P. occidentalis f. attenuata Sarg., 1919.
  4. ↑ Other names: P. palmata Moench, 1794; P. umbrosa Salisb., 1796; P. cuneata Willd., 1797; P. elongata Steud., 1821; P. undulata Steud., 1821; P. macrophylla Cree ex W.H. Baxter, 1839; P. nepalensis Hort. ex W.H. Baxter, 1839; P. digitata Hort. ex Steud., 1841; P. vulgaris Spach, 1841; P. algeriensis Hort. ex K.Koch, 1872; P. laciniata Hort. ex K.Koch, 1872; P. nana Hort. ex K.Koch, 1872; P. reuteri Hort. ex K.Koch, 1872; P. umbraculifera Hort. ex K. Koch, 1872; P. insularis Kotschy ex Koehne, 1893; P. pyramidalis Bolle ex Koehne, 1893; P. vitifolia Dippel, 1893; P. cretica Dode, 1908; P. orientalior Dode, 1908.

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