Including Castanaceae Link
Habit and leaf form. Trees and shrubs. Mesophytic. Leaves deciduous; medium-sized, or large; opposite; petiolate; compound; palmate (3-11 foliolate). Lamina palmately veined; cross-venulate. Leaves exstipulate. Lamina margins (of the leaflets) crenate, or serrate. Vegetative buds scaly (and usually sticky). Domatia recorded; represented by hair tufts.
Leaf anatomy. Lamina dorsiventral. Minor leaf veins with phloem transfer cells (Aesculus).
Stem anatomy. Cork cambium present. Nodes tri-lacunar, or multilacunar. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. `Included' phloem absent. Xylem with libriform fibres; with vessels. Vessel end-walls simple, or scalariform and simple. Wood ring porous; partially storied (VP, VPR); parenchyma apotracheal and paratracheal.
Reproductive type, pollination. Andromonoecious (usually, the upper, first-opening flowers male), or hermaphrodite, or polygamomonoecious (some flowers effectively female, by shedding of immature stamens). Gynoecium of male flowers vestigial. Entomophilous; via hymenoptera (bees).
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in `inflorescences'. The terminal inflorescence unit cymose. Inflorescences terminal; large racemes of cincinni. Flowers medium-sized to large; very irregular; zygomorphic. The floral asymmetry involving the perianth, or involving the perianth and involving the androecium (and often also the disk). Flowers cyclic; tetracyclic to pentacyclic. Free hypanthium absent. Hypogynous disk present; extrastaminal; annular (or unilateral).
Perianth with distinct calyx and corolla; (9-)10; 2 whorled; isomerous, or anisomerous. Calyx 5; 1 whorled; almost polysepalous (Billia), or gamosepalous (Aesculus); when gamosepalous, lobed; campanulate, or tubular; unequal but not bilabiate, or regular; imbricate. Corolla (4-)5 (the middle of the lower three members sometimes missing); 1 whorled; polypetalous; imbricate; unequal but not bilabiate; with contrasting markings (with yellow spots, which later turn red). Petals clawed.
Androecium (5-)6-8 (the inner whorl of five complete, the outer more or less reduced). Androecial members free of the perianth; markedly unequal; free of one another; 2 - whorled. Androecium exclusively of fertile stamens. Stamens (5-)6-8; reduced in number relative to the adjacent perianth to isomerous with the perianth; alternisepalous, or oppositisepalous. Anthers dorsifixed (near the base); versatile; dehiscing via longitudinal slits; introrse; tetrasporangiate. Microsporogenesis simultaneous. Tapetum glandular. Pollen grains aperturate; 3 - aperturate; colporate; 2-celled.
Gynoecium (2-)3(-4). Carpels reduced in number relative to the perianth. Gynoecium syncarpous; eu-syncarpous; superior. Ovary (2-)3(-4) locular. The `odd' carpel anterior. Ovary sessile. Gynoecium stylate. Styles 1; attenuate from the ovary; apical. Stigmas 1; 1 - lobed, or (2-)3(-4) - lobed; dry type; papillate; Group II type (B(i)). Placentation axile. Ovules 2 per locule; pendulous to ascending (sometimes the lower ascending, the upper pendulous); superposed; non-arillate; anatropous, or amphitropous, or orthotropous; bitegmic; crassinucellate. Outer integument contributing to the micropyle. Embryo-sac development Polygonum-type (?). Endosperm formation nuclear.
Fruit non-fleshy; dehiscent; a capsule (smooth to echinate). Capsules loculicidal (large, leathery, often one-loculed by abortion). Fruit 1 seeded (often, by abortion), or 2-5 seeded. Seeds non-endospermic; large (with a large hilum reflecting incorporation of the funicle in the placenta, and adnation of the placental obturator). Embryo well differentiated. Cotyledons 2 (often with one much larger than the other, often adherent face to face). Embryo chlorophyllous (1/1); curved.
Seedling. Germination cryptocotylar.
Physiology, biochemistry. Not cyanogenic. Iridoids absent. Proanthocyanidins present; cyanidin. Flavonols present; kaempferol, or kaempferol and quercetin. Ellagic acid absent (Aesculus). Arbutin absent. Saponins/sapogenins present, or absent. Aluminium accumulation not found. C3. C3 recorded in Aesculus.
Geography, cytology. Holarctic, Paleotropical, and Neotropical. Temperate to tropical. North temperate and Central and South America. X = 20.
Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren's Superorder Rutiflorae; Sapindales. Cronquist's Subclass Rosidae; Sapindales. Takhtajan's Subclass Rosidae; Rutanae; Sapindales. Species 15. Genera 2; Aesculus, Billia.
Economic uses, etc. Some cultivated ornamentals, notable horse-chestnut (Aesculus hippocastanum) which is widely planted in temperate regions.
Illustrations. hippo357.gif
