1	Flower yellow; leaves reniform to broadly ovate, apex rounded or obtuse		Viola biflora
+	Flower purple or white		(2)
2 (1)	Plants without stems or stolons; stipule adnate to petiole more than 1/2 of length		(3)
+	Plants with stems or stolons		(7)
3 (2)	Stipule adnate to petiole, less than 2/3 of length; basal petal rounded at apex; rhizome long creeping, nodose; leaves triangular-ovate		Viola senzanensis
+	Stipule adnate to petiole, up to 3/4 of length; basal petal truncate or emarginate at apex; rhizome short, stout		(4)
4 (3)	Roots dark brown		Viola mandshurica
+	Roots white or yellowish brown		(5)
5 (4)	Spur slender, 2.5-6 mm long, lateral petals usually beardless		Viola confusa
+	Spur short, up to 3.5 mm long, lateral petals bearded		(6)
6 (5)	Upper petals usually bearded		Viola betonicifolia
+	Upper petals beardless		Viola inconspicua ssp. nagasakiensis
7 (2)	Petioles winged; basal petal shortest, acute or acicular at apex		(8)
+	Petiole wingless		(11)
8 (7)	Flower less than 1.5 cm across; plants with stems and stolons		(9)
+	Flower more than 1.5 cm in diameter; plants without stems		(10)
9 (8)	leaves cuneate or shallowly cordate at base; lateral petals usually bearded		Viola diffusa
+	Leaves cordate at base; lateral petals usually beard-less		Viola tenuis
10 (8)	Leaves ovate, lateral petals beardless		Viola nagasawai var. nagasawai
+	Leaves triangular-ovate, lateral petals bearded		Viola nagasawai var. pricei
11 (7)	Basal petal truncate or emarginate at apex		(12)
+	Basal petal rounded or obtuse at apex		(16)
12 (11)	Flowers small less than 1.5 cm in diameter		Viola arcuata
+	Flowers large, more than 2 cm in diameter		(13)
13 (12)	Spur slender, more than 4 mm long; basal petal longest, emarginate at apex		(14)
+	Spur rounded, less than 2 mm long, basal petal shortest, truncate or emarginate at apex		(15)
14 (13)	Leaves orbicular or orbicular-cordate, rounded or obtuse at apex		Viola formosana var. formosana
+	Leaves cordate, acute at apex		Viola formosana var. stenopetala
15 (13)	Leaves membraneous, usually hirsute; lateral petals usually bearded		Viola adenothrix var. adenothrix
+	Leaves chartaceous to subcoriaceous, usually glabrous; lateral petals usually beardless		Viola adenothrix var. tsugitakaensis
16 (11)	Lateral petals bearded; style papillose at apex; capsule globose		Viola shinchikuensis
+	Lateral petals beardless; style smooth at apex; capsule ellipsoid		(17)
17 (16)	Leaf-blades cordate, usually as long as or shorter than wide		Viola grypoceras
+	Leaf-blades triangular ovate, usually longer than wide		Viola obtusa var. tsuifengensis