Iris japonica Thunb.

Flowering from March to April; fruiting from May to June.

Iris japonica is close relative of Iris formosana, but differs from the latter in flowering stems with 5-12 (vs. 4 or 5) branches, 4.5-5.5 cm (vs. 7-8 cm) flowers in diameter.

Iris japonica is occurring in Anhui, Fujian, Gansu, Guangdong, Guangxi, Guizhou, Hainan, Hubei, Hunan, Jiangsu, Jiangxi, Qinghai, Shaanxi, Shanxi, Sichuan, Xizang, Yunnan, Zhejiang of China, Japan, Myanmar.

Phylogenetic analyses of Iris representing all subgenera and all sections except Regelia, Brevituba, and Monolepis, were inferred from matK gene and trnK intron sequence data (Wilson, 2004). Sequence data show that Iris is paraphyletic because Belamcanda chinensis is resolved within the genus. The two largest subgenera, Iris and Limniris, are both resolved as polyphyletic. With the removal of section Hexapogon, subgenus Iris is weakly supported as monophyletic. Relationships within subgenus Limniris are more complex with the subgenus as currently circumscribed representing eight independent origins. Several potential monophyletic groups are identified including subgenus Scorpiris, series Spuria (subgenus Limniris section Limniris), and a clade of section Limniris species from North America and Asia.

Rhizomes dimorphic: suberect, thick; creeping, long, slender. Leaves basal, dark or yellowish green, glossy on 1 surface, dull on other, reddish purple at base, sword-shaped, 25-60 cm long, 1.5-3 cm wide, midvein absent. Flowering stems erect, with 5-12 short, slender branches near apex; spathes 3-5, broadly lanceolate, 0.8-1.5 cm, 2-4-flowered, apex obtuse. Flowers pale bluish, 4.5-5.5 cm in diameter; pedicel 1.5-2.5 cm, stiff, persistent. Perianth tube 1.1-1.5 cm; outer segments obovate or elliptic, 2.5-3 × 1.4-2 cm, limb spreading, with blue blotching around central, yellow patch around prominent, yellow crest, margin denticulate, undulate, apex retuse; inner segments spreading obliquely, elliptic or narrowly obovate, 2.8-3 × 1.5-2.1 cm, margin denticulate, undulate. Stamens 0.8-1.2 cm; anthers white. Ovary 7-10 mm. Style branches pale blue; terminal lobes fimbriate. Capsule ellipsoid-cylindric, 2.5-3 × 1.2-1.5 cm, apex not beaked. Seeds dark brown, with small aril.

The chromosomal number of Iris japonica is 2n = 24, 28, 34, 36, 54, 56 (Mao and Xue, 1986; Colasante and Sauer, 1993; Dong et al., 1994).

Growing in open forest margins, wet grasslands; 500-800 m (2400-3400 m in SW China).