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; without marked odour; simple; epulvinate. Lamina entire (usually), or dissected; when dissected, palmatifid (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 occurring in the family (Hydrangea); manifested as 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. Plants 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 ultimate 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); blunt-lobed to toothed; regular (except in outer,sterile flowers when these present); imbricate, or valvate. Epicalyx absent. 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; unappendaged. Pollen shed as single grains. Pollen grains aperturate; 3 aperturate; colpate, or colporate.
Gynoecium (2–)3–5 carpelled. Carpels reduced in number relative to the perianth to isomerous with the perianth. The pistil 1–5 celled. Gynoecium syncarpous; synovarious to synstylovarious; partly inferior to inferior. Ovary 1 locular (‘incompletely plurilocular’), or 2–3(–5) 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. Micropyle not zigzag.
Physiology, biochemistry. Cyanogenic, or not cyanogenic. Cynogenic constituents tyrosine-derived (triglochinin?), or phenylalanine-derived. Iridoids detected; ‘Route I’ type (normal and seco). 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. APG 3 core angiosperms; core eudicot; Superorder Asteranae; Order Cornales.
Species 115. Genera 10; Broussaisia, Cardiandra, Decumaria, Deinanthe, Dichroa, Hydrangea, Kirengeshoma, Pileostegia, Platycrater, Schizophragma.
• Technical details: Hydrangea, Decumaria.
• Technical details: Hydrangea (Lindley).
• Hydrangea macrophylla var. hortensia: as H. japonica, Bot. Reg. 1844, 61.