Hydrangea Family Hydrangea Family

Craig C. Freeman

Subshrubs, shrubs, trees, or vines [herbs], evergreen or deciduous. Leaves usually opposite, sometimes whorled [alternate], simple; stipules absent; petiole present or absent; blade sometimes palmately lobed, margins entire, serrate, serrulate, dentate, denticulate, or crenate; venation pinnate or acrodromous (Fendlera, Fendlerella, Philadelphus, Whipplea). Inflorescences terminal or axillary, cymes, panicles, racemes, or corymbs, or flowers solitary. Flowers bisexual [unisexual], or sometimes marginal ones sterile, radially symmetric (bisexual ones) or bilaterally symmetric with enlarged petaloid sepals (sterile ones); perianth and androecium nearly hypogynous, perigynous, or epigynous; hypanthium completely adnate to ovary or adnate to ovary proximally, free distally; sepals 4–12, distinct or connate basally; petals 4–12, connate basally [entirely, then calyptrate]; nectary usually present, rarely absent; stamens 8–200, usually distinct, sometimes connate proximally, free; anthers dehiscing by longitudinal slits; pistil 1, 2–12-carpellate, ovary less than 1/2 inferior, 1/2 inferior, or completely inferior, 1–12-locular, placentation usually axile proximally, parietal distally, rarely strictly axile or parietal; ovules 1–50 per locule, anatropous; styles 1–12, distinct or connate proximally to most of length; stigmas (1–)2–12. Fruits capsules [berries], dehiscence septicidal, loculicidal, interstylar, or intercostal. Seeds 1–50 per locule, funicular appendage present (Fendlerella, Whipplea) or absent.

Genera 17, species ca. 240 (9 genera, 25 species in the flora): North America, Mexico, Central America, South America, Eurasia, Pacific Islands.

A. Cronquist (1981) placed Hydrangeaceae among a group of woody families traditionally allied with Saxifragaceae. Phylogenetic studies consistently place Hydrangeaceae in the Cornales and sister to Loasaceae (A. L. Hempel et al. 1995; D. E. Soltis et al. 1995; L. Hufford et al. 2001; Hufford 2004). Within Hydrangeaceae, the western North American genera Fendlera and Jamesia form a clade (subfam. Jamesioideae L. Hufford) that is sister to the rest of the family (subfam. Hydrangeoideae Burnett) (Hufford et al.; Hufford). Subfamily Hydrangeoideae comprises two tribes: Philadelpheae de Candolle ex Duby and Hydrangeeae de Candolle. North American genera in the former are Carpenteria, Deutzia, Fendlerella, Philadelphus, and Whipplea. A molecular phylogenetic study by Y. De Smet et al. (2015) clarified relationships within Hydrangeeae, found Hydrangea to be polyphyletic, and promoted adoption of a broader concept of Hydrangea that includes the eight other genera in the tribe. The two North American genera in the tribe, Decumaria and Hydrangea, are circumscribed here in their traditional senses.

The Hydrangeaceae are well represented in the paleobotanical record dating back to the Upper Cretaceous but best represented in the Tertiary (L. Hufford 2004). Some genera are sources of popular introduced or native ornamentals, including Carpenteria, Deutzia, Hydrangea, and Philadelphus. Some ornamentals have become established outside of cultivation in the flora area. A few North American Hydrangeaceae have reputed medicinal (D. E. Moerman 1998) or toxicologic (G. E. Burrows and R. J. Tyrl 2001) properties.

Trichomes in most Hydrangeaceae consist of a long, unicellular portion, often borne on a multicellular base. The unicellular portion often bears tubercles on its surface. Sometimes instead of tubercles, it bears long extensions, making the trichome appear branched or dendritic. Such trichomes are here referred to as branched.

SELECTED REFERENCES De Smet, Y. et al. 2015. Molecular phylogenetics and new (infra)generic classification to alleviate polyphyly in tribe Hydrangeeae (Cornales: Hydrangeaceae). Taxon 64: 741–752. Hufford, L. 1995. Seed morphology of Hydrangeaceae and its phylogenetic implications. Int. J. Plant Sci. 156: 555–580. Hufford, L. 1997. A phylogenetic analysis of Hydrangeaceae based on morphological data. Int. J. Plant Sci. 158: 652–672. Hufford, L. 1998. Early development of androecia in polystemonous Hydrangeaceae. Amer. J. Bot. 85: 1057–1067. Hufford, L. 2004. Hydrangeaceae. In: K. Kubitzki et al., eds. 1990+. The Families and Genera of Vascular Plants. 10+ vols. Berlin etc. Vol. 6, pp. 202–215. Hufford, L., M. L. Moody, and D. E. Soltis. 2001. A phylogenetic analysis of Hydrangeaceae based on sequences of the plastid gene matK and their combination with rbcL and morphological data. Int. J. Plant Sci. 162: 835–846. Small, J. K. and P. A. Rydberg. 1905. Hydrangeaceae. In: N. L. Britton et al., eds. North American Flora.... 1905+. New York. 47+ vols. Vol. 22, pp. 159–178. Soltis, D. E., Xiang Q. Y., and L. Hufford. 1995. Relationships and evolution of Hydrangeaceae based on rbcL sequence data. Amer. J. Bot. 82: 504–514. Spongberg, S. A. 1972. The genera of Saxifragaceae in the southeastern United States. J. Arnold Arbor. 53: 409–498.