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The families of flowering plants

L. Watson and M.J. Dallwitz

Hippocastanaceae DC.

~ Sapindaceae.

Including Aesculaceae Lindl., Aesculaceae Berchtold & Presl, Castanaceae Link, Paviaceae Horan.

Habit and leaf form. Trees and shrubs. Mesophytic. Leaves deciduous; medium-sized, or large; opposite; petiolate; not gland-dotted; 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 occurring in the family; manifested as hair tufts.

Leaf anatomy. The leaf lamina dorsiventral. Hairs present; unicellular and multicellular. Unicellular hairs simple. Multicellular hairs uniseriate. Complex hairs absent. The mesophyll containing crystals. The crystals druses and solitary-prismatic. Main veins vertically transcurrent, or embedded. Minor leaf veins with phloem transfer cells (Aesculus).

Axial (stem, wood) anatomy. Cork cambium present. Nodes tri-lacunar, or multilacunar. Primary vascular tissues in a cylinder, without separate bundles; collateral. Internal phloem absent. Cortical bundles absent. Medullary bundles absent. Secondary thickening developing from a conventional cambial ring. Primary medullary rays narrow (uniseriate only, or some biseriate in Billia).

The wood ring porous. The vessels usually numerous, very to moderately small; solitary, radially paired, in radial multiples, and clustered. The vessel end-walls simple, or scalariform and simple. The vessels without vestured pits; with spiral thickening, or without spiral thickening. The axial xylem with tracheids, or without tracheids; without vasicentric tracheids; with fibre tracheids, or without fibre tracheids; with libriform fibres; including septate fibres, or without septate fibres. The fibres without spiral thickening. The parenchyma apotracheal and paratracheal. The secondary phloem not stratified. ‘Included’ phloem absent. The wood storied, or partially storied (VP, VPR). Tyloses present, or absent.

Reproductive type, pollination. Plants 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. Pollination entomophilous; via hymenoptera (bees).

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’. The ultimate inflorescence units cymose. Inflorescences terminal; large racemes of cincinni. Flowers medium-sized to large; very irregular; zygomorphic. The floral irregularity 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, blunt-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) carpelled. Carpels reduced in number relative to the perianth. The pistil (2–)3(–4) celled. 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); when not orthotropous, apotropous (Engler); 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; thick and fleshy, often with one much larger than the other, often adherent face to face. Embryo chlorophyllous (1/1); curved.

Seedling. Germination cryptocotylar.

Physiology, phytochemistry. C3. C3 physiology recorded directly in Aesculus. Sugars transported as sucrose. Not cyanogenic. Arbutin absent. Iridoids not detected. Saponins/sapogenins present, or absent. Proanthocyanidins present; cyanidin. Flavonols present; kaempferol, or kaempferol and quercetin. Ellagic acid absent (Aesculus). Aluminium accumulation not found.

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. APG III core angiosperms; core eudicot; Superorder Rosanae; malvid. APG IV Order Sapindales (as a synonym of Sapindaceae).

Species 15. Genera 2; Aesculus, Billia.

General remarks. Separable from Sapindaceae by the opposite, palmate leaves and relatively large flowers, otherwise differing only in characters relying on limited sampling (leaf phloem transfer cells and stigma details).

Economic uses, etc. Some cultivated ornamentals, notably the horse-chestnut (Aesculus hippocastanum) which is widely planted in temperate regions.


Under the spreading chestnut tree

Horse Chestnuts are given to horses . . . to cure them of coughe, shortnesse of winde, and other such diseases
(Parkinson, 1640. But the name more likely indicated their inferiority to Sweet Chestnuts, and ‘by a process only too well known in early botanical literature, was afterwards taken as proof of their medicinal value’: Edward Step, ‘Wayside and Woodland Trees’, 1905)

Then the prickly balls are bursting
On the bending chestnut trees
(George Heath, ‘September’, c. 1865)

Illustrations. • Le Maout and Decaisne: Aesculus. • Aesculus glabra: as A. ohiotensis, Bot. Reg. XXIV, 51 (1838). • Aesculus hippocastanum: Hutchinson.

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.’.