An erect perennial herb; stolons creeping; stems terete, with small black spots, 30-60 cm high, simple or with few branches above. Leaves subopposite or alternate, elliptical or lanceolate, 4-7 cm long, 1-2 cm wide, the apex acute or obtuse, entire, sessile or subsessile. Racemes terminal, densely many-flowered, 10-20 cm long, glabrous or minutely glandular hairy, the pedicels short, about 3 mm long; the bracts acicular 3-5 mm long. Flowers white, 5-6 mm across; calyx 5-parted, segments ovate-oblong, acute or obtuse, membraneous and ciliate at margine, with black glandular dots, ca. 2 mm long; corolla-lobes oblong, rounded, obtuse, ca. 3-5 mm long; stamens 5, inserted on the petals, filaments short, ca. 0.5 mm long; anthers broadovate, ca. 0.6 mm long; ovary globose, style ca. 1 mm long. Capsules globose, 2-2.5 mm in diameter, style persistent. Flowers: May-Jul.
TAIPEI: Linkou, Peng 8585; Pinghsi, Wang 1377. ILAN: Taipingshan, Suzuki s. n. 1925. TAOYUAN: Yangmei, Kuo 11119; Taoyuan, Suzuki 4638. HSINCHU: Lienhuashih, Peng 7231; Hukou, Peng 7244. NANTOU: Sun Moon Lake, Kudo & Sasaki 15399.
Distributed inJapan, Korea, the Ryukyus, Indo-China, and SE China. Taiwan, in wet places by rivers and ponds in lowlands, in northern part of the island.
Phenology: perennial
Life form: herb
Root: rooting at node or not: not rooting at node
Stem: present
Stem: type: erect
Stem: shape: terete
Stem: indumentum: glabrous
Leaf: position: cauline
Phyllotaxy: opposite
Leaf: petiole: sessile
Leaf: blade shape: elliptic, lanceolante
Leaf: blade apex: acute
Leaf: blade base: attenuate
Leaf: blade margin: entire
Leaf: blade surface: glabrous
Leaf: blade texture: herbaceous
Leaf: blade length (mm): 40-70
Leaf: blade width (mm): 10-20
Inflorescence: raceme
Inflorescence: position: terminal
Scape: absent
Peduncle: length (mm): 1.2-3
Bract: present
Bract: length (mm): 2-5
Bract: width (mm): 0
Calyx: shape: 5-parted
Sepal: shape: ovate, oblong
Sepal: margin: ciliolate
Sepal: length (mm): 1.2-1.8
Sepal: width (mm): 0.8-1.3
Corolla: color: white
Corolla: shape: rotate
Lobe: margin: entire
Lobe: length (mm): 2-5
Lobe: width (mm): 1-1.5
Filament fused into a ring or not: filament free
Filament inserted position: base of corolla lobe
Filament: indumentum: glabrous
Filament and anther relative length: filament obviously longer than anther
Stamens protruding from corolla or not: Stamens protuding from corolla
Capsule: dehiscence type: longitudinal
Distribution: wet places by rivers and ponds
