Flora of North America species comparison

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Hydrangeaceae

Hydrangea

hydrangea family, mock-orange family

graybeard, hortensia, hydrangea, sevenbark
Habit Subshrubs, shrubs, trees, or vines [herbs], evergreen or deciduous. Shrubs or trees.
Stems

erect, ascending, or spreading.
Bark

exfoliating in grayish, brown, or reddish brown sheets.
Branches

erect, ascending, or spreading, sometimes arching;

twigs with simple or branched trichomes.
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).

deciduous, opposite or 3-whorled;

petiole present;

blade ovate, elliptic-ovate, elliptic, or suborbiculate, sometimes lobed, herbaceous, margins serrate to serrulate, plane;

venation pinnate.
Inflorescences

terminal or axillary, cymes, panicles, racemes, or corymbs, or flowers solitary.

terminal, cymose panicles, 100–1000-flowered;

peduncle present.
Pedicels

present.
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.

bisexual or marginal ones often sterile (these with a petaloid, salverform calyx);

perianth and androecium epigynous or perigynous;

hypanthium campanulate or hemispheric, completely adnate to ovary, weakly or strongly 7–10(–11)-ribbed in fruit;

sepals persistent, 5, spreading or reflexed, deltate to shallowly triangular, usually glabrous, rarely abaxially sparsely hairy;

petals 5, valvate, spreading or reflexed, white to yellowish white, ovate-lanceolate, elliptic, oblong, spatulate, or narrowly ovate to ovate, base sessile, surfaces glabrous;

stamens 10;

filaments distinct, terete or flattened proximally, gradually or abruptly tapered from base to apex, apex not 2-lobed;

anthers depressed-ovoid or transversely oblong;

pistil 2–4-carpellate, ovary completely inferior or nearly so, or 1/2 inferior, 2–4-locular;

placentation axile proximally, parietal distally;

styles persistent, 2–4, distinct or connate to middle or distally.
Fruits

capsules [berries], dehiscence septicidal, loculicidal, interstylar, or intercostal.

Capsules

hemispheric, suburceolate, or oblong-ovoid, coriaceous, dehiscence interstylar, creating elliptic to circular pore at base of styles.
Seeds

1–50 per locule, funicular appendage present (Fendlerella, Whipplea) or absent.

10–40 per locule, light brown to dark brown, fusiform or ellipsoid.
x

= 18.

Hydrangeaceae

Hydrangea
Distribution
North America; Mexico; Central America; South America; Eurasia; Pacific Islands
[BONAP county map]
from USDA
United States; Mexico; Central America; w South America; e Asia
[BONAP county map]
Discussion

Genera 17, species ca. 240 (9 genera, 25 species in the flora).

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.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Species ca. 29 (5 in the flora).

Hydrangea enjoys considerable esteem as an ornamental shrub, especially for its prominent sterile flowers. North American species have been cultivated in Europe since before the mid 1700s (W. L. Stern 1978). Besides the species treated here, popular ornamentals in North America are H. anomala D. Don, H. aspera D. Don, H. heteromalla D. Don, H. involucrata Siebold, H. macrophylla (Thunberg) Seringe, and H. serrata (Thunberg) Seringe. Among these, H. macrophylla may be the most widely grown; M. A. Dirr (2004) listed nearly 170 cultivars of this species. Surprisingly, it has not escaped from cultivation.

Tubercles, comprising crystals of calcium carbonate, often are visible on leaf trichomes (G. W. Burkett 1932). They are observed most easily at magnifications greater than 30\x, and some taxonomic utility has been ascribed to their presence and abundance.

Toxic and medicinal properties are attributed to some native and cultivated species of Hydrangea (J. M. Kingsbury 1964; W. L. Stern 1978; D. E. Moerman 1998; G. E. Burrows and R. J. Tyrl 2001). These possibly are related to various alkaloids present in roots and leaves of some species.

Y. De Smet et al. (2015) found Hydrangea to be polyphyletic and promoted adoption of a broader, monophyletic concept of Hydrangea that includes all eight genera in tribe Hydrangeeae. Both North American genera in the tribe, Decumaria and Hydrangea, are circumscribed here in their traditional senses.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
1. Woody vines.
Decumaria
1. Subshrubs, shrubs, or trees.
→ 2
2. Twigs with stellate and simple trichomes.
Deutzia
2. Twigs glabrous or with simple or, sometimes, branched trichomes, never with stellate trichomes.
→ 3
3. Flowers both sterile and bisexual.
Hydrangea
3. Flowers all bisexual.
→ 4
4. Stamens (11–)13–90 or 150–200.
→ 5
5. Sepals 4; petals 4 (or 8+ in some horticultural forms); ovaries inferior to 1/2 inferior, 4-locular; styles 1 or 4; leaves deciduous; stamens (11–)13–90.
Philadelphus
5. Sepals 5–7; petals 5–7(–8); ovaries nearly superior, 5–7-locular; styles 1; leaves persistent; stamens 150–200.
Carpenteria
4. Stamens 8–12.
→ 6
6. Stems prostrate to decumbent.
Whipplea
6. Stems erect, ascending, or spreading.
→ 7
7. Filament apices 2-lobed, lobes prolonged beyond anthers; seeds (1–)2–4(–6) per locule.
Fendlera
7. Filament apices not 2-lobed; seeds 1 or 10–50 per locule.
→ 8
8. Inflorescences 100–1000-flowered; capsule dehiscence interstylar, creating pore at base of styles.
Hydrangea
8. Inflorescences 1–35-flowered; capsule dehiscence septicidal.
→ 9
9. Leaf blade margins usually crenate to dentate, rarely entire; blades ovate or broadly ovate to obovate, rhombic, or suborbiculate, venation pinnate; seeds 25–50 per locule.
Jamesia
9. Leaf blade margins entire; blades elliptic to lanceolate, oblanceolate, obovate, or linear-oblong, venation acrodromous; seeds 1 per locule.
Fendlerella
1. Leaf blades (3–)5(–7)-lobed, margins coarsely serrate; inflorescences ovoid to conic.
H. quercifolia
1. Leaf blades unlobed, margins dentate, serrate, or serrulate; inflorescences dome-shaped to hemispheric or conic to ovoid.
→ 2
2. Ovaries 1/2 inferior; inflorescences usually conic, sometimes ovoid.
H. paniculata
2. Ovaries completely inferior or nearly so; inflorescences dome-shaped to hemispheric.
→ 3
3. Leaf blade abaxial surfaces white or grayish, densely tomentose, trichomes at 40× either smooth, 1–3 mm, or sparsely tuberculate, 0.3–1 mm.
H. radiata
3. Leaf blade abaxial surfaces green, glabrous or glabrate, or grayish, uniformly velutinous, pilose, or tomentose, trichomes at 40× conspicuously tuberculate, 0.3–1 mm.
→ 4
4. Leaf blade abaxial surfaces green, glabrous or glabrate, or sparsely hirsute along midveins and sometimes along lateral veins.
H. arborescens
4. Leaf blade abaxial surfaces grayish, uniformly velutinous, pilose, or tomentose.
H. cinerea
Source FNA vol. 12, p. 462. Treatment author: Craig C. Freeman. FNA vol. 12, p. 486. Treatment author: Craig C. Freeman.
Parent taxa Hydrangeaceae
Subordinate taxa
Carpenteria, Decumaria, Deutzia, Fendlera, Fendlerella, Hydrangea, Jamesia, Philadelphus, Whipplea
H. arborescens, H. cinerea, H. paniculata, H. quercifolia, H. radiata
Name authority Dumortier Linnaeus: Sp. Pl. 1: 397. (1753): Gen. Pl. ed. 5, 189. (1754)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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