Korea Flora: Deciduous shrub. Height 1-1.5m. Branches gray or dark gray, with scattered lenticels. Branchlets hollow. Leaves opposite, broadly ovate, abruptly acuminate apex, cuneate or slightly cordate base, size 4-6(7)cm × 3-4(5)cm. Both surfaces hairless, upper surface dark green, lower surface grayish-green, margins with small teeth or almost entire. Petiole 8-10mm long. Flowers bisexual, 1(2) in leaf axils, but 6-8 clustered on opposing branches, flower stalks barely developed (1mm). Flowers appear before leaves. Flowers tetramerous, 3.5cm wide, petals 15-18mm long and oblong. Corolla tube 4mm long, bright yellow, sepals broadly ovate. Fruit and seed: ovoid, 10-13mm × 6-7mm, 5mm thick, flat and smooth, small fruit stalk 2-3mm long. Seeds polygonal, 5-6mm × 1.5-2mm.

Flowering mid-March (Gyeonggi-do), April (Gangwon-do area).

Fruiting August-September.

Distribution: Western Honshu, Japan; Northern Gangwondo and Hwanghaedo, Korea.

Taxonomic notes: According to Kim's (1999) recent study, among the Forsythia species in Korea, F. ovata is grouped with Japan's F. japonica and China's inland F. viridissima, while F. koreana is grouped with F. saxatilis and northeastern China's F. mandschurica Uyeki. Markgraf (1930), studying mainly cultivated specimens, treated F. ovata as a synonym of Japanese F. japonica, and following Rehder's opinion, treated F. koreana as a variety of F. viridissima and F. saxatilis as a synonym of F. viridissima. In contrast, Green (1997) recognized F. saxatilis as a variety of F. japonica based on the presence of hair, while recognizing the hairless F. ovata as a species. These research results show considerable disagreement, but Kim's cpDNA study results and Markgraf's opinions mostly agree, except for the relationship between F. viridissima and F. koreana. Here, Markgraf's opinion is largely accepted. The presence or absence of hair in F. koreana (vs. F. saxatilis) and F. ovata (vs. Japanese F. japonica) is not considered an important characteristic, and F. nakaii is viewed as a variation of F. ovata.

Japan Flora: Deciduous shrub; branches grayish yellow-brown, nearly terete, with 2 shdlow obscure grooves or indistinctly 4-striate, glabrous; leaves mem­branous, ovate to broadly so, 7-12(-15) cm. long, 4-6(-8) cm. wide, short-acuminate, usually toothed, glabrous, pale green and more or less white-hairy, especially on the nerves beneath, the petioles 6-8 mm. long, white-pubescent; pedicels 2-3 mm. long, slightly shorter than the bud-scales; calyx-lobes elliptic, 25-3 mm. long, ciliate; corolla about 2.5 cm. across, the lobes narrowly oblong, about 12 mm. long, 5-6 mm. wide; fruit broadly ovoid, about 1 cm. long.  Apr. Mountains.

Hon­shu (Chugoku Distr.); rare.