Hydrangeaceae Dum.

Including Kirengeshomaceae (Engl.) Nak.

Excluding Philadelphaceae

Habit and leaf form. Shrubs (or subshrubs), or herbs, or lianas (in Decumaria). Plants non-succulent. Self supporting (usually), or climbing. Leaves evergreen, or deciduous; alternate, or opposite; petiolate; when opposite connate to not connate; gland-dotted, or not gland-dotted; simple; epulvinate. Lamina entire (usually), or dissected; when dissected, palmately lobed (e.g. Kirengeshoma); pinnately veined, or palmately veined; cross-venulate. Leaves exstipulate. Lamina margins entire, or serrate, or dentate. Vegetative buds scaly. Leaves without a persistent basal meristem. Domatia recorded (Hydrangea); represented by hair tufts.

Leaf anatomy. Hairs present, or absent. Complex hairs absent.

Adaxial hypodermis present, or absent. Lamina dorsiventral; with secretory cavities (sometimes, gland-dotted), or without secretory cavities. The mesophyll containing calcium oxalate crystals. The mesophyll crystals commonly raphides. Minor leaf veins without phloem transfer cells (Hydrangea).

Stem anatomy. Cork cambium present; initially deep-seated. Secondary thickening developing from a conventional cambial ring. Xylem with tracheids. Vessel end-walls scalariform, or scalariform and simple. Wood parenchyma absent or apotracheal (with a few cells around the vessels).

Reproductive type, pollination. Hermaphrodite (or sometimes the outer flowers of the aggregates sterile), or polygamodioecious (Broussaisia).

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in `inflorescences'; in cymes, or in heads, or in corymbs, or in racemes (by reduction). The terminal inflorescence unit cymose. Inflorescences cymose or corymbose, sometimes capitate, sometimes racemose by abortion; pseudanthial (with more or less petal-like outer flowers), or not pseudanthial. Flowers small, or medium-sized; regular, or somewhat irregular; 4-10 merous; cyclic. Free hypanthium present (brief), or absent.

Perianth with distinct calyx and corolla; 8-24; 2 whorled; isomerous. Calyx 4-5(-10); 1 whorled; polysepalous (rarely), or gamosepalous (usually); lobed to toothed; regular (except in outer,sterile flowers when these present); imbricate, or valvate. Corolla 4-5(-10); 1 whorled; polypetalous; imbricate, or contorted, or valvate; regular.

Androecium 4, or 8, or 10-200. Androecial members branched (when `many', from a limited number of `trunks'), or unbranched; when stamens numerous, maturing centripetally; free of the perianth; free of one another, or coherent (sometimes the filaments slightly connate basally); (1-)2-15 - whorled (sometimes in `several series'). Androecium exclusively of fertile stamens. Stamens 4-100 (i.e. to `many'); isomerous with the perianth, or diplostemonous to polystemonous (more often). Filaments not appendiculate. Anthers dorsifixed (Kirenghesoma), or dorsifixed to basifixed; versatile; dehiscing via longitudinal slits; introrse. Pollen shed as single grains. Pollen grains aperturate; 3 - aperturate; colpate, or colporate.

Gynoecium (2-)3-5. Carpels reduced in number relative to the perianth to isomerous with the perianth. Gynoecium syncarpous; synovarious to synstylovarious; partly inferior to inferior. Ovary 1 locular (`incompletely plurilocular'), or 2-3 locular. Epigynous disk usually present (atop the ovary). Gynoecium stylate. Styles (2-)3-5; free to partially joined; apical. Stigmas dry type; papillate; Group II type ((b)). Placentation when unilocular, intrusive parietal; when plurilocular, axile. Ovules in the single cavity (when unilocular) 20-100 (`many'); (when plurilocular) 15-50 per locule (`many'); anatropous; unitegmic; tenuinucellate. Endothelium differentiated. Polar nuclei fusing prior to fertilization. Synergids hooked. Endosperm formation cellular.

Fruit fleshy (rarely), or non-fleshy; dehiscent (usually), or indehiscent; a capsule (usually), or a berry. Capsules when capsular, loculicidal. Fruit many seeded. Seeds endospermic; winged, or wingless. Embryo well differentiated. Cotyledons 2. Embryo achlorophyllous (1/1); straight.

Physiology, biochemistry. Cyanogenic, or not cyanogenic. Cynogenic constituents tyrosine-derived (triglochinin?), or phenylalanine-derived. Iridoids recorded; carbocyclic and seco-compounds. Proanthocyanidins present, or absent; cyanidin, or delphinidin. Flavonols present; quercetin, or kaempferol and quercetin. Ellagic acid absent (3 genera, 3 species). Arbutin present. Aluminium accumulation demonstrated.

Geography, cytology. Holarctic and Neotropical. Temperate to sub-tropical. Widespread North temperate and subtropical, and Andes from Mexico to Chile. X = 13-18(+).

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren's Superorder Corniflorae; Cornales. Cronquist's Subclass Rosidae; Rosales. Takhtajan's Subclass Rosidae; Rosanae; Saxifragales. Species 115. Genera 10; Broussaisia, Cardiandra, Decumaria, Deinanthe, Dichroa, Hydrangea, Kirengeshoma, Pileostegia, Platycrater, (Pottingeria?), Schizophragma.

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