Family Platanaceae

Platanaceae Dum.

Habit and leaf form. Large trees; 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. Leaves without a persistent basal meristem. Domatia occurring in the family (8 species); manifested as pockets.

Leaf anatomy. Stomata more or less anomocytic.

Lamina isobilateral (but the abaxial palisade cells shorter). Minor leaf veins without phloem transfer cells.

Stem anatomy. Cork cambium present; initially superficial (the bark scaling off in large flakes, leaving the trunk smooth). Nodes multilacunar (7). Internal phloem absent. Secondary thickening developing from a conventional cambial ring. ‘Included’ phloem absent. Xylem with fibre tracheids; with vessels. Vessel end-walls scalariform and simple. Vessels without vestured pits. Wood parenchyma apotracheal (diffuse or in uniseriate bands). Sieve-tube plastids S-type.

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

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 3 core angiosperms; peripheral eudicot; Superorder Proteanae; Order Proteales.

Species 10. Genera 1; only genus, Platanus.

Illustrations.
• Technical details: Platanus.