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The families of flowering plants

L. Watson and M.J. Dallwitz

Platanaceae Dum.

Habit and leaf form. Large trees. Plants green and photosynthesizing. Leptocaul. Mesophytic. Leaves deciduous; medium-sized, or large; alternate (sometimes to subopposite on vigorously growing shoots); spiral; flat; petiolate (the petiole base enclosing the axillary bud); sheathing (via the stipules); simple. Lamina nearly always dissected (merely toothed in P. kerrii); nearly always palmatifid; palmately veined (nearly always), or pinnately veined (P. kerrii); cross-venulate. Leaves stipulate. Stipules concrescent (around the stem); ochreate; scaly; caducous. Lamina margins dentate; flat. Vegetative buds scaly. Leaf development not ‘graminaceous’. Domatia occurring in the family (recorded in 8 species); manifested as pockets.

Leaf anatomy. The leaf lamina bifacial (but the abaxial palisade cells shorter). Stomata more or less anomocytic. Hairs present; eglandular, or eglandular and glandular (the former including those constituting the dense, woolly tomentum of deciduous candelabra hairs (see illustration) which can inflame human mucous membranes, as well as less branched and occasional uniseriate forms; the latter, when present, are represented by simple capitate glands and sometimes by hairs with gland-tipped branches). The mesophyll containing crystals. The crystals druses. Minor leaf veins without phloem transfer cells.

Axial (stem, wood) anatomy. Cork cambium present; initially superficial (the bark scaling off in large flakes, leaving the trunk smooth). Nodes multilacunar (7). Primary vascular tissues comprising a ring of bundles (the xylem being dissected by broad rays, the widened ends of which separate the groups of phloem); collateral. Internal phloem absent. Cortical bundles absent. Medullary bundles absent. Secondary thickening developing from a conventional cambial ring. Primary medullary rays wide, or wide and mixed wide and narrow.

The vessels moderately small; mainly solitary and in radial to tangential pairs and threes. The vessel end-walls scalariform and simple. The vessels without vestured pits. The axial xylem with fibre tracheids; without libriform fibres; without septate fibres. The fibres without spiral thickening. The parenchyma apotracheal (diffuse or in uniseriate bands). ‘Included’ phloem absent. The wood not storied. Tyloses present (often), or absent.

Reproductive type, pollination. Fertile flowers functionally male and functionally female. Plants monoecious (the unisexual clusters in separate inflorescences). Female flowers with staminodes (commonly, 3–4), or without staminodes (?). Gynoecium of male flowers vestigial, or absent. Pollination anemophilous.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in heads. Inflorescences consisting of pendulous strings of up to 12 dense, globose, sessile or pedunculate heads of flowers, each infloresence exclusively either male or female. Flowers bracteate, or ebracteate (depending on interpretation of the ‘scales’); small; regular; cyclic. Floral receptacle not markedly hollowed. Free hypanthium absent. Hypogynous disk absent.

Perianth with distinct calyx and corolla (or at least, so interpretable, in male flowers), or sepaline (the female flowers lacking any semblance of a corolla); 3–4(–7), or 6–8(–14); free, or joined; 1 whorled, or 2 whorled; isomerous; different in the two whorls. Calyx 3–4(–7) (not vascularized); 1 whorled; polysepalous, or gamosepalous (sometimes united basally); regular. Corolla in male flowers 3–4(–7) (tiny or vestigial); 1 whorled; polypetalous.

Androecium 3–4(–7). Androecial members free of the perianth; all equal; free of one another; 1 whorled. Androecium exclusively of fertile stamens. Stamens 3–4(–7); isomerous with the perianth; oppositisepalous; filantherous (the filaments very short), or with sessile anthers. Anthers basifixed, or adnate; non-versatile; dehiscing by longitudinal valves; latrorse; bilocular; tetrasporangiate; appendaged (via the peltate connective). Microsporogenesis simultaneous. Tapetum probably glandular. Pollen grains aperturate; 3 aperturate, or 4 aperturate (rupate), or 6 aperturate; colpate (3-), or rugate (6-); 2-celled.

Gynoecium (3–)5–8(–9) carpelled. Carpels isomerous with the perianth, or increased in number relative to the perianth. Gynoecium apocarpous; eu-apocarpous (in 2–3 whorls); superior. Carpel incompletely closed (distally); non-stylate; apically stigmatic (the papillate stigma decurrent along the apical style); 1(–2) ovuled. Placentation apical to marginal. Ovules pendulous; orthotropous; bitegmic; crassinucellate.

Fruit non-fleshy; an aggregate. The fruiting carpel indehiscent; an achene, or nucular (with accrescent, pappose hairs from the base). Gynoecia of adjoining flowers combining to form a multiple fruit. Fruit 1 seeded. Seeds scantily endospermic. Endosperm oily. Embryo well differentiated. Cotyledons 2. Embryo straight (slender).

Seedling. Germination phanerocotylar.

Physiology, phytochemistry. C3. C3 physiology recorded directly in Platanus. Cyanogenic. Cynogenic constituents tyrosine-derived. Alkaloids absent (2 species). Arbutin absent. Iridoids not detected. Saponins/sapogenins absent. Proanthocyanidins present; cyanidin and delphinidin. Flavonols present; kaempferol, quercetin, and myricetin. Ellagic acid absent (2 species). Aluminium accumulation not found. Sieve-tube plastids S-type.

Geography, cytology. Temperate (warm). Scattered, North temperate, North America, Southeast Europe, Southern and Eastern Asia. X = 7. Supposed basic chromosome number of family: 7.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Rosiflorae; Hamamelidales. Cronquist’s Subclass Hamamelidae; Hamamelidales. APG III core angiosperms; peripheral eudicot; Superorder Proteanae. APG IV Order Proteales.

Species 10. Genera 1; only genus, Platanus.

Illustrations. • Le Maout and Decaisne: Platanus. • Platanus orientalis: Hutchinson. • Leaf hair of Platanus occidentalis: Solereder, 1908.

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 15th April 2018.’.