| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### Hydrangeaceae Dum.

Including Kirengeshomaceae (Engl.) Nak.; excluding Philadelphaceae.

Habit and leaf form. Shrubs (or subshrubs), or herbs, or lianas (in Decumaria); non-laticiferous, without coloured juice. Plants green and photosynthesizing. Self supporting (usually), or climbing. Leaves persistent, or deciduous; alternate, or opposite; petiolate; when opposite connate to not connate; gland-dotted, or not gland-dotted; without marked odour; with blades ‘normally orientated’; 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. Leaf development not ‘graminaceous’. Domatia occurring in the family (in Hydrangea); manifested as hair tufts.

Leaf anatomy. The leaf lamina dorsiventral. Stomata at least sometimes paracytic (in Dichroa and Hydrangea). Hairs present, or absent (inadequately described). Complex hairs absent (?). Adaxial hypodermis present, or absent. Lamina with secretory cavities (sometimes, gland-dotted), or without secretory cavities. The mesophyll containing crystals. The crystals commonly raphides. Minor leaf veins without phloem transfer cells (Hydrangea).

Axial (stem, wood) anatomy. Secretory cavities absent. Cork cambium present; initially deep-seated. Primary vascular tissues in a cylinder, without separate bundles; collateral. Cortical bundles absent. Medullary bundles absent. Secondary thickening developing from a conventional cambial ring.

The wood ring porous to diffuse porous. The vessels very numerous, small; mainly solitary. The vessel end-walls scalariform, 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, or without libriform fibres; including septate fibres (rarely), or without septate fibres. The fibres without spiral thickening. The parenchyma absent or apotracheal (with a few cells around the vessels). The secondary phloem not stratified. ‘Included’ phloem absent. The wood not storied.

Reproductive type, pollination. Unisexual flowers present, or absent. 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 units 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. 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 (1–)3–5; free to partially joined; apical. Stigmas dorsal to the carpels; 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, phytochemistry. Cyanogenic, or not cyanogenic. Cynogenic constituents tyrosine-derived (triglochinin?), or phenylalanine-derived. Arbutin present. 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). 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 III core angiosperms; core eudicot; Superorder Asteranae. APG IV Order Cornales.

Species 115. Genera 10; Broussaisia, Cardiandra, Decumaria, Deinanthe, Dichroa, Hydrangea, Kirengeshoma, Pileostegia, Platycrater, Schizophragma.

Illustrations. • Le Maout and Decaisne: Hydrangea, Decumaria. • Deinanthe bifida: Hook. Ic. Pl. 19 (1889). • Deinanthe caerulea: Bot. Mag. 137 (1911). • Decumaria sinensis: Hook. Ic. Pl. 18 (1887). • Hydrangea virens: Lindley. • Hydrangea macrophylla var. hortensia: as H. japonica, Bot. Reg. 1844, 61. • Hydrangea petiolaris: Bot. Mag. 110 (1884). • Hydrangea robusta (as H. cyanema): Bot. Mag. 84 (1858). • Hydrangea wallichii (as Adamia cyanea): Bot. Mag. 58 (1831). • Kirengeshoma palmata: Bot. Mag. 130 (1904). • Schizophragma hydrangeoides: Bot. Mag. 139 (1913). • Schizophragma integrifolia: Hook. Ic. Pl. 20 (1890).

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: 8th June 2026. delta-intkey.com’.

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