Shinyleaf meadowsweet, dwarf spiraea

Spiraea betulifolia Pallas var. corymbosa (Rafinesque) Maximowicz; S. ostryfolia Rafinesque; S. repens Rafinesque; S. sororia Penny ex G. Don

Shrubs, 3–10(–15) dm. Stems erect to arching, branched. Leaves: petiole 3–8 mm, ˂sparsely hairy˃; blade ovate to elliptic or suborbiculate, 2–10 × 1–2.5 cm, coriaceous, base obtuse, rounded, or subcordate, margins irregularly, coarsely and sharply doubly serrate from midpoint to apex, ˂teeth acute and mucronate, number of primary and secondary serrations 1 times number of secondary veins (excluding inter-secondary veins)˃, venation pinnate cladodromous, secondary veins not prominent, apex acute, obtuse, or rounded, abaxial surface mostly glabrous, adaxial glabrous. Inflorescences mostly terminal, corymbiform, 2–5 × 3–10 cm ˂height 0.4–1.1 times diam.˃; branches ˂rarely in axils of leaves˃, glabrous or glabrate. Pedicels 1–3 mm, glabrous or glabrate. Flowers 4–7 mm diam.; hypanthia hemispheric, 0.8–1 mm, abaxial surface glabrous or pubescent, adaxial glabrous; sepals triangular, 0.5–1 mm; petals chalky white to pink, orbiculate, 1.3–1.5 mm; staminodes 5–15 ˂reduced to serrations˃; stamens 15–20, 2 times petal length. Follicles nearly fusiform, 2–3 mm, ˂shiny˃, glabrous. 2n = 36.

Flowering May–Oct; fruiting Jun–Nov. Open rocky soil, rocky, lightly wooded sites, dry or fast draining slopes, rocky edges of woods; 0–500 m; N.S., Ont.; Ga., Md., Mass., N.J., N.C., Pa., Tenn., Va., W.Va.; introduced in e Europe.

H. A. Gleason and A. Cronquist (1963) and L. J. Uttal (1974) considered Spiraea corymbosa to be a variety of S. betulifolia. K. Sax (1936) found S. corymbosa to be a triploid with complete pollen sterility and hypothesized that it must exist as a diploid, or form viable egg cells, because it is involved in hybrids. If so, these cytological differences may be correlated with some morphological variation.