5. Deutzia Thunberg, Nov. Gen. Pl. 19. 1781.
[For Johann van der Deutz, ca. 1743–1784, Dutch merchant and patron of Carl Peter Thunberg] [For Johann van der Deutz, ca. 1743–1784, Dutch merchant and patron of Carl Peter Thunberg]
Ronald L. McGregor†
Shrubs. Stems erect to spreading. Bark exfoliating in grayish, brownish, or reddish sheets or flakes. Branches erect, ascending, spreading, or arching; twigs with stellate and simple trichomes. Leaves deciduous or semideciduous, opposite; petiole present; blade lanceolate, elliptic, or ovate, herbaceous, margins serrulate to crenate-denticulate, plane; venation pinnate. Inflorescences terminal, corymbose cymes, panicles, or racemes, usually (2–)5–60-flowered, rarely flowers solitary; peduncle present or absent. Pedicels present. Flowers bisexual; perianth and androecium epigynous; hypanthium completely adnate to ovary, campanulate or ovoid, not ribbed in fruit; sepals deciduous, 5, erect, triangular to broadly ovate, glabrous or abaxially short-hairy or stellate-pubescent; petals 5 [10 in some cultivars], valvate or imbricate, spreading, white, pink, or purplish, elliptic to oblong, base clawed, surfaces glabrous or hairy; stamens 10, in 2 whorls; filaments distinct, dorsiventrally flattened or terete, gradually or abruptly tapered medially or filiform, apex 2-lobed or not lobed; anthers globose; pistil 3–5-carpellate, ovary completely inferior, 3–5-locular; placentation usually axile proximally and parietal distally, sometimes strictly parietal; styles persistent, 3(–4), distinct. Capsules hemispheric, cartilaginous, dehiscence acropetally septicidal along septum at base of fruit and also apically. Seeds 10–20 per locule, dark brown, ellipsoid. x = 13.
Species ca. 60 (3 in the flora): introduced; Mexico, Asia (China, Himalaya, Japan, Korea), Pacific Islands (Philippines).
A. J. Rehder (1940) recognized 23 species (including eight named hybrids), 27 varieties, and about 27 cultivars of Deutzia growing mostly at the Arnold Arboretum. L. H. Bailey et al. (1976) listed taxa only in the horticultural trade and cited 34 species and 36 cultivars that had been listed in the previous two decades. M. A. Dirr (1998) reported that Deutzia has lost favor as an ornamental over the years. He noted that identification of species, particularly cultivars, borders on the impossible, and nothing is clear-cut in the world of Deutzia identification. He listed seven species and 22 cultivars, including nine cultivars of D. scabra.
In cultivation, deutzias may spread by suckers; several species have escaped and become marginally naturalized. M. L. Fernald (1950) reported that Deutzia gracilis and D. scabra were beginning to spread to thickets and roadsides; there is no evidence that either species has become widely naturalized. H. A. Gleason and A. Cronquist (1991) noted that D. scabra rarely escapes from cultivation.