Japan Flora: Glabrous or nearly glabrous shrub, branches terete; leaves rhombic-ovate, broadly ovate, oblong or narrowly obovate, 1.5-35 cm. long, 1-3 cm. wide, obtuse to subrounded or subacute at apex, broadly cuneate to obtuse at base, irregu­larly toothed or incised except on the lower half, sometimes 3-lobed, the lateral nerves slightly impressed above, raised beneath, tlie petioles 3-10 mm. long; inflorescence umbellate, rather many-flowered; pedicels 10-15 mm. long, slender; flowers white, 6-8 mm. across; calyx-teeth erect, narrowly deltoid, acute; petals orbicular, as long as or slightly shorter than the stamens; fruiting carpels glabrous or slightly hairy on ventral side. May. Mountains;

Honshu (Kinki Distr. and westw.), Shikoku, Kyushu. Very variable.

var. pubescens (Koidz.) Ohwi. Young branches and inflorescence short-pubescent. Shikoku.

var. hayatae (Koidz.) Ohwi. Leaves gla­brous or slightly pubescent beneath; inflorescence, young branchlets, and fruit pubescent. Honshu (Chugoku Distr.).

Korea Flora: Deciduous shrub, 1m tall. Branchlets glabrous; previous year’s branches reddish-brown. Leaves alternate, ovate or nearly orbicular, shallowly lobed in the upper half, obtuse apex, rounded or broadly cuneate base, 2-3.5(4)cm × 2.5-3cm; glabrous on both surfaces. Upper surface dark green, lower surface grayish-green, veins prominent, 3-5 pairs of lateral veins; margins with rounded teeth but apically acute. Petioles 5mm long, glabrous. Inflorescences umbellate-racemose, bearing 15-20 flowers per cluster, 3cm across. Flowers 8mm in diameter, white; pedicels 10mm long, glabrous. Calyx lobes acuminate, 2mm long, glabrous; petals orbicular or broader than long; stamens shorter than petals. Fruits follicles, 1.5-2mm long.

Chromosome number: 18, 36.
Flowering: Mid-May to late July.
Fruiting: Mid-October.

Distribution: Southern to northern China, southern Honshu to Kyushu (Japan); Hwanghae , Gangwon , and Ulleungdo Island (Korea).

Ecological note: Forms small clusters on rocky ridges in mountainous areas.

Taxonomic note: Spiraea trilobata shows some variation in leaf shape and pedicel length but is likely an individual variation of Spiraea blumei. While it is recognized as a distinct species in Russia and China, the limited specimen analysis suggests that synonymy should be considered cautiously. Differences between S. blumei and S. trilobata show significant overlap in variation. Some populations with narrowly elliptic leaves and entire margins, or with slight serrations only at the distal end, have been referred to as S. pseudocrenata Nakai. However, these are also likely individual variations within S. blumei.