Leaves either palmately 3-foliolate, or sometimes pinnately 3- or rarely to 9-foliolate; stipules partly united and fused to petioles, often sheathing.
Inflorescences often head-like, spicate or umbellate, usually many-flowered; bracts small or absent; bracteoles absent. Calyx tubular or campanulate, with 5 equal to unequal teeth. Corolla often persistent in pod; keel shorter than wings. Stamens diadelphous; all filaments, or 5 of them, dilated at apex; anthers uniform.
Pod usually indehiscent, ovoid to linear; seeds usually 1 or 2 (rarely 4–9), without a conspicuous aril.
Many species are widely cultivated as pasture plants and most of these have become naturalized, growing most commonly on disturbed sites such as roadsides, gardens, lawns and pastures.
| | Key to the species | |
| 1 | Leaves with terminal petiolule distinctly longer than lateral ones; corolla yellow | 2 |
| Leaves with terminal petiolule equal to lateral ones; corolla white, cream or pink to red | 3 |
| 2 | Standard spoon-shaped in pod; inflorescences globose, many-flowered | Trifolium campestre |
| Standard boat-shaped in pod; inflorescences semiglobose, 3–20-flowered
Back to 1 | Trifolium dubium |
| 3 | Inflorescences with 3–16 fertile flowers with corollas and numerous sterile ones without corollas | 4 |
| All flowers fertile
Back to 1 | 5 |
| 4 | Inflorescences with 3–6 fertile flowers; fruiting heads penetrating the ground; inflorescences axillary; corolla not persistent in fruit; pod exserted from calyx | Trifolium subterraneum |
| Inflorescences with 10–16 fertile flowers; fruiting heads aerial; inflorescences terminal; corolla persistent in fruit; pod included in calyx
Back to 3 | Trifolium globosum |
| 5 | Calyx tube inflated and vesiculous in pod | 6 |
| Calyx tube unchanged or distended in pod
Back to 3 | 8 |
| 6 | Flowers resupinate; corolla not persistent in fruit; annuals | 7 |
| Flowers not resupinate; corolla persistent in fruit; perennials
Back to 5 | 22 |
| 7 | Peduncles longer than subtending leaves; inflorescences globose; calyx teeth spiny; calyx throat glabrous | Trifolium resupinatum |
| Peduncles shorter than subtending leaves; inflorescences umbellate; calyx teeth blunt; calyx throat with a ring of hairs
Back to 6 | Trifolium tomentosum |
| 8 | Inflorescences sessile, overtopped by broad membranous stipules | Trifolium suffocatum |
| Inflorescences sessile or pedunculate, not overtopped by stipules
Back to 5 | 9 |
| 9 | Flowers pedicellate, often shortly so | 10 |
| Flowers sessile
Back to 8 | 15 |
| 10 | Inflorescences 1–5-flowered | Trifolium ornithopodioides |
| Inflorescences more than 8-flowered
Back to 9 | 11 |
| 11 | Peduncle shorter than subtending leaf, or inflorescence sessile | 12 |
| Peduncle longer than subtending leaf
Back to 10 | 13 |
| 12 | Pod included in calyx; calyx teeth blunt | Trifolium glomeratum |
| Pod exserted from calyx; calyx teeth spiny
Back to 11 | Trifolium cernuum |
| 13 | Pedicels of only the lower flowers deflexed after anthesis; calyx teeth equal to subequal; pod included in calyx | Trifolium ambiguum |
| Pedicels of all flowers deflexed after anthesis; calyx teeth unequal; pod exserted from calyx
Back to 11 | 14 |
| 14 | Calyx teeth erect in pod; plants not rhizomatous; calyx with 5 prominent and 5 inconspicuous veins | Trifolium hybridum |
| Calyx teeth spreading in pod; plants rhizomatous; calyx with 10 more or less equally conspicuous veins
Back to 13 | Trifolium repens |
| 15 | Leaflet margins entire, or nearly so | 16 |
| Leaflet margins toothed, sometimes finely so
Back to 9 | 18 |
| 16 | Peduncle longer than subtending leaf; calyx teeth equal | Trifolium arvense |
| Peduncle shorter than subtending leaf; calyx teeth unequal
Back to 15 | 17 |
| 17 | Leaves 3-foliolate; leaflets 1–2 times as long as broad; calyx throat narrowed by an annular thickening in pod; teeth blunt, erect in pod; corolla persistent in pod; stipules abruptly narrowed to a bristly apex | Trifolium pratense |
| Leaves 3-foliolate; leaflets 12–15 times as long as broad; calyx throat closed by a 2-lipped callosity in pod, teeth spiny, spreading in pod; corolla not persistent in pod; stipules subulate
Back to 16 | Trifolium angustifolium |
| 18 | Corollas persistent in pod | 19 |
| Corollas not persistent in pod
Back to 15 | 20 |
| 19 | Corolla 5–7 mm long, pink; calyx tube 10-veined, teeth spiny | Trifolium striatum |
| Corolla 15–17 mm long, purple; calyx tube 20-veined, teeth blunt
Back to 18 | Trifolium hirtum |
| 20 | Inflorescences sessile; calyx teeth unequal | Trifolium scabrum |
| Inflorescences pedunculate; calyx teeth equal to subequal
Back to 18 | 21 |
| 21 | Flowers cream, bracteolate; pod included in calyx; calyx teeth blunt | Trifolium alexandrinum |
| Flowers usually red to purple, without bracteoles; pod exserted from calyx; calyx teeth spiny
Back to 20 | Trifolium incarnatum |
| 22 | Corolla 6–8 mm long; calyx pilose. | Trifolium fragiferum |
| Corolla 12–15 mm long; calyx glabrous.
Back to 6 | Trifolium vesiculosum |
