Leaves alternate, cauline or radical; lamina ± circular to lanceolate, margins toothed, crenate or ± entire, petiolate; stipules present, usually leafy.
Flowers solitary on axillary scapes with a pair of bracteoles near or below the middle. Sepals produced into small basal appendages. Lower petal spurred or pouched at base, lateral petals often bearded within. Anthers with a flat membranous appendage; the 2 lowest anthers with a spur at the base. Ovary glabrous or hairy; style usually bent.
Key in part modified from Thiele & Prober (2003) New Species and a new hybrid in the Viola hederacea species complex, with notes on Viola hederacea Labill. Muelleria 18: 7–25
| | Key to the species | |
| 1 | Annual or biennial; stipules to 4 cm long, green, deeply lobed; lower petal broad-cuneate | Viola arvensis |
| Perennials; stipules small, often brownish, translucent; lower petal ovate to linear-oblong | 2 |
| 2 | Plants not stoloniferous but stems sometimes elongated and decumbent; lower petal spurred; flowers scentless; styles thickened towards apex | 3 |
| Plants stoloniferous, stems rarely elongated; lower petal shallowly pouched but lacking a spur or if spurred then flowers sweetly scented;style not apically thickened
Back to 1 | 5 |
| 3 | Stems lax, elongated; leaves cauline, lamina heart-shaped | 4 |
| Stems erect, short; leaves radical, lamina lanceolate to oblong, the base cuneate or shallowly cordate
Back to 2 | Viola betonicifolia |
| 4 | Stipules frimbriate; corolla blue violet; uncommon garden escape (recorded only in Central Tablelands in NSW) | Viola riviniana |
| Stipules entire or sparcely toothed; corolla white or rarely pale violet (recorded from coast and tableland regions of NSW)
Back to 3 | Viola caleyana |
| 5 | Petiole with short deflexed hairs, flowers strongly scented; lower petal spurred; capsule hairy | Viola odorata |
| Petiole glabrous, or if hairy the hairs not deflexed; flowers scentless or faintly scented; lower petal not spurred; capsule usually glabrous
Back to 2 | 6 |
| 6 | Flowers on short scapes hidden among the leaves; petals scarsely exceeding the sepals | 7 |
| Flowers on scapes as long or longer than the leaves; petals clearly longer than the sepals
Back to 5 | 8 |
| 7 | Flowers blackish-violet; lower petal c. 2 mm wide, obovate or elliptic; usually montaine plants | Viola fuscoviolacea |
| flowers cream or white, often with a purplish tinge towards the centre; lower petal c. 1 mm wide, linear to oblong; lowland plants
Back to 6 | Viola cleistogamoides |
| 8 | Well developed leaves twice as wide as long or wider; flowers concolorous pale bluish; stems often caulescent; habitat on sandstone in New South Wales | Viola silicestris |
| Leaves not much wider than long, or, if about twice as wide as as long then flowers distinctly discolourous
Back to 6 | 9 |
| 9 | Anterior petal more or less rectangular | 10 |
| Anterior petal ovate, almost circular or obovate-obcuneate
Back to 8 | 11 |
| 10 | Flowers more or less concolorous pale blue; plants small; leaf base usually cuneate, tapering to petiole | Viola sieberiana |
| Flowers discolorous dark violet and paler violet; plants robust, often trailing; leaf base usually broadly cordate
Back to 9 | Viola sp. Sassafras (K.R.Thiele 5425) |
| 11 | Anterior petal broadest in the distal third, its venation usually somewhat irregular, petals petals with indistinct demarcation between violet and white colouration; seeds dull, cream to brown, usually mottled | 12 |
| Anterior petal broadest in the proximal third or the middle, regularly triplinerved, petals with distinct demarcation between violet and white colouration; seeds glossy purple-black
Back to 9 | 13 |
| 12 | Leaves usually more or less semicircular, glabrous to sparsely hairy; flowers usually discolorous, deep violet in the centre, gradually blending into white at the tips | Viola hederacea |
| Leaves suborbicular to reniform with a deep sinus, softly hairy; flowers more or less concolorous, violet to the tips but often white in the centre
Back to 11 | Viola perreniformis |
| 13 | Anterior petal broadest in the middle; leaves reniform to orbicular, about as long as wide, often with a deep, narrow sinus; lowland, often coastal plants | Viola banksii |
| Anterior petal usually broadest in the proximal third; leaves reniform, wider than long, with a broad sinus or truncate; alpine to montaine plants in eastern Australia (at lower altitudes in SA)
Back to 11 | Viola eminens |
