Hydrangeaceae Dumort.

First published in Anal. Fam. Pl. 36, 38. 1829 (1829)nom. cons.
This family is accepted

Descriptions

Timothy M. A. Utteridge and Laura V. S. Jennings (2022). Trees of New Guinea. Kew Publishing. Royal Botanic Gardens, Kew

Distribution
A family of 8 genera with c. 200 species, distributed in warm temperate regions of the New and Old World but absent from Africa and Madagascar; a single genus in New Guinea.
[TONG]

Milliken, W., Klitgard, B. and Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics. http://creativecommons.org/licenses/by/3.0

Morphology General Habit
Shrubs, vines and lianas
Morphology Leaves
Leaves simple, opposite, stipules absent, entire, margins often crenate or serreate, stellate hairs often present
Morphology Reproductive morphology Inflorescences
Inflorescence terminal or axillary, cymose, in Hydrangea with sterile flowers at tips of outer branches
Morphology Reproductive morphology Flowers
Flowers showy or small, hermaphrodite, actinomorphic; sepals 4-5, united forming a short tube; petals 4-5,  free, white, or pink, sometimes with purple blotch at base in Philadelphus; stamens (4-)5-10 or >15, free, anthers 2-locular; ovary inferior, 2-4 carpellate, incompletely bi-locular, styles fused in Philadelphus, separate in Hydrangea and Deutzia, placentation axile and or parietal, ovules many.  Fruit capsular, variously dehiscent, many seeded; seeds small, testa reticulate .
Note
Notes on delimitation: Recent studies place this family close to the Cornaceae (APG II, 2003) in order Cornales. Number of genera: Deutzia Thunb. - Temperate Asia and North America south to Mexico, 2 - 3 species. Hydrangea L. - Temperate Asia, reaching Mexico, 5 - 10 species. Philadelphus L. - Temperate Asia and North America, reaching Mexico, 5 - 6 species.
Distribution
In the Neotropics the Hydrangeaceae is a marginal family with a few genera ocurring at high altitude and reaching Mexico from the West of the USA, and only Hydrangea (Hydrangea peruviana Moric. ex Ser.) reaching Peru and Chile. Apart from cultivated species, this family is absent from Brazil. Many cultivars of Hydrangea are popular plants in cooler climates in South America. The family as a whole is not a very expressive family in the region, with only a few species ocurring only marginally in the area.
Diagnostic
Key differences from similar families: The opposite leaves and inferior ovary might cause confusion with families included in the Gentianales (Rubiaceae and others), Caprifoliaceae, Lamiales. The free petals and stamens twice as many as petals found in Hydrangeaceae are good characters to separate them. Stellate hairs. Sterile flowers at the edge of inflorescences. Stamens often twice as many as petals or more. Distinguishing characters (always present): Rootclimbers or shrubs. Leaves opposite, simple, margin rarely entire. Flower 4-5-merous, petals free. Ovary inferior, often with separate styles. Key to genera of Neotropical Hydrangeaceae 1. Inflorescences in large terminal corymbs often with sterile outer flowers ... Hydrangea 1. Inflorescences smaller, axillary, flowers all fertile ... 2 2. Flowers pentamerous, petals 5 ... Deutzia 2. Flowers tetramerous, petals 4 ... Philadelphus
[NTK]

Gemma Bramley, Anna Trias-Blasi & Richard Wilford (2023). The Kew Temperate Plant Families Identification Handbook. Kew Publishing Royal Botanic Gardens, Kew

Recognition
Characters of similar families: Cornaceae: perianth 4(–5)-merous, stamens 4(–5), fruits drupaceous berries. Viburnaceae: flowers usually 5-merous, fruits drupes or berries. Caprifoliaceae: flowers usually 5-merous, synsepalous, synpetalous. Rubiaceae: interpetiolar stipules, margins always entire, flowers usually 5-merous.
Morphology General Habit
Trees, (sub)shrubs or vines, evergreen or deciduous
Morphology Leaves Stipules
Stipules absent
Morphology Leaves
Leaves simple, usually opposite; blade sometimes palmately lobed, margins entire, serrate, serrulate, dentate, denticulate, or crenate; venation pinnate or acrodromous
Morphology Reproductive morphology Inflorescences
Inflorescences terminal or axillary, cymes, panicles, racemes, or corymbs, or flowers solitary
Morphology Reproductive morphology Flowers
Flowers generally bisexual, radially symmetric; marginal flowers sometimes sterile and bilaterally symmetric with enlarged petaloid sepals; perianth with hypanthium completely adnate to ovary or adnate to ovary proximally, free distally; sepals 4–12, distinct or connate basally; petals 4–12, usually connate basally; nectary usually present; stamens 8–200, usually distinct, sometimes connate proximally; anthers dehiscing by longitudinal slits; pistil 1, 2–12-carpellate; ovary partly or completely inferior, 1–12-locular, placentation usually axile proximally, parietal distally; ovules 1–50 per locule, anatropous; styles 1–12, distinct or connate; stigmas (1–)2–12
Morphology Reproductive morphology Fruits
Fruit usually a capsule, dehiscence septicidal, loculicidal, interstylar, or intercostal, rarely a berry
Morphology Reproductive morphology Seeds
Seeds 1–50 per locule.
Distribution
Hydrangeaceae has its largest diversity in North America, also native from Asia to the Pacific Islands, and from Central to South America. Introduced in Europe. The family includes 9 genera (ca. 217 species). Major genera include Deutzia (ca. 73 species), Philadelphus (ca. 52 species) and Hydrangea (ca. 80 species).
Note
Woody plants. Stipules absent. Leaves simple, opposite. Flowers bisexual, sometimes marginal flowers sterile; perianth 4–12-merous; nectary usually present; stamens 8–200; pistil 1, styles 1–12. Fruit usually a capsule.
Description Author
Isabel Larridon
[KTEMP-FIH]

Sources

  • Kew Names and Taxonomic Backbone

    • The International Plant Names Index and World Checklist of Vascular Plants 2025. Published on the Internet at http://www.ipni.org and https://powo.science.kew.org/
    • © Copyright 2023 International Plant Names Index and World Checklist of Vascular Plants. http://creativecommons.org/licenses/by/3.0
  • Neotropikey

    • Milliken, W., Klitgard, B. and Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics.
    • http://creativecommons.org/licenses/by-nc-sa/3.0
  • Trees of New Guinea

    • Trees of New Guinea
    • http://creativecommons.org/licenses/by-nc-sa/3.0
  • The Kew Temperate Plant Families Identification Handbook

    • The Kew Temperate Plant Families Identification Handbook
    • http://creativecommons.org/licenses/by-nc-sa/3.0