Spiraea chamaedryfolia
Sp. Pl. 1: 489. 1753.
Shrubs, 10–20 dm. Stems erect, densely branched. Leaves: petiole 5–10 mm; blade ovate to ovate-lanceolate, 4–8 × 1.5–4 cm, membranous, base obtuse, margins usually coarsely, irregularly, sharply serrate to serrulate in distal 2/3, sometimes 2-serrate, venation pinnate simple craspedodromous, secondary veins not prominent, apex acute, surfaces glaucous, glabrous. Inflorescences mostly axillary, racemiform, corymbiform, or hemispheric panicles, (2–)3–10 × 2–5 cm; branches glabrous. Pedicels 5–10 mm, glabrous. Flowers 5–12 mm diam.; hypanthia campanulate, 1.5–2 mm, abaxial surface glabrous, adaxial glabrous to puberulent; sepals ovate-triangular, 2.5–3 mm; petals white, broadly ovate, 4–6 mm, apex notched or erose; staminodes 0; stamens 35–50, 2 times petal length. Follicles asymmetrical fusiform, 2–3 mm, glabrous or pubescent. 2n = 18.
Phenology: Flowering May–Jul; fruiting Jun–Oct.
Habitat: Old pastures, homestead sites
Elevation: 0–700 m
Distribution
Ont., Conn., N.Y., se Europe, Asia (China, Japan, Russia), introduced also in w Europe.
Discussion
Two frequently mentioned varieties of Spiraea chamaedryfolia are var. ulmifolia (Scopoli) Maximowicz, which has primarily ovate leaves with an obtuse base and a frequently doubly-serrate margin and inflorescences 7–10 cm diam., treated as a species by Rydberg, and var. flexuosa (Fischer ex Cambessèdes) Maximowicz, which has ovate-lanceolate leaves with cuneate base and entire or singly-serrate margin with fewer teeth and inflorescences 4–6 cm diam. Variation in the leaf and inflorescence characters is inconsistent in plants established in North America. C. Sterling (1966) described the carpel anatomy of this species but did not examine enough taxa from Europe or Asia for comparison. W. J. Bean (1970–1988, vol. 4) and H. S. Maxwell and S. G. Knees (1989) are useful references for additional information on varieties and hybrids of this Eurasian native.
Selected References
None.