Key to Common Annual Clovers

The key works by selecting one of the two choices given for each pair of descriptions, which lead to either another pair of descriptions or the identification of your species.

1.	Leaves with the terminal leaflet having a distinctly longer stalk than the lateral leaflets, flowers yellow	2
1.	Leaves with the stalk of the terminal leaflet being more or less equal to the lateral leaflet stalks, flowers white or pink	3
2.	Flower-heads nearly globular, 30-50 flowered and flowers closely overlapping	Hop Clover (Trifolium campestre)
2.	Flower-heads hemispherical, 3-20 flowered and flowers not closely overlapping	Suckling Clover (Trifolium dubium)
3.	Flower-heads of 3-6 fertile, white with pink striped flowers; fruiting heads pushed into the ground by the hardened and deflexed calyces (sepal whorls)	Subterranean Clover (Trifolium subterraneum)
3.	Flower-heads of at least 8 fertile, white, pink or purple flowers; fruiting heads not pushed into the ground	4
4.	Calyx (outer leaf-like flower whorl) tube inflated, bladdery in fruit	5
4.	Calyx tube not inflated or bladdery in fruit	6
5.	Flower stalks longer than the leaves at their base; flower-heads nearly globular, flowers pink to purplish; calyx teeth spiny	Persian Clover (Trifolium resupinatum)
5.	Flower stalks shorter than the leaves at their base; flower-heads umbrella-like, flowers pink; calyx teeth blunt	Woolly Clover (Trifolium tomentosum)
6.	Leaves long and narrow, 5-15 times as long as wide; flowers white, pink or purplish	7
6.	Leaves not long and narrow, less than 4 times as long as wide; flowers usually pink	8
7.	Flower-heads 30-80 mm long; flower-stalks shorter than the leaves at their base; calyx tube as long as the teeth	Narrow-leaf Clover (Trifolium angustifolia)
7.	Flower-heads 10-20 mm long; flower stalks longer than the leaves at their base; calyx tube much shorter than the teeth	Hare’s-foot Clover (Trifolium arvense)
8.	Flower stalks longer than the leaves at their base	Balansa Clover (Trifolium michelianum)
8.	Flower stalks shorter than the leaves at their base	9
9.	Plants hairy	Knotted Clover (Trifolium striatum)
9.	Plants hairless except occasionally for a few hairs at the base of the leaflets and on the calyx	10
10.	Individual flower-stalks about 2 mm long and becoming recurved in fruit; calyx teeth erect with maturity	Drooping-flower Clover (Trifolium cernuum)
10.	Individual flower-stalks less than 1 mm long or stalkless and not reflexing in fruit; calyx teeth spreading with maturity	Clustered Clover (Trifolium glomeratum)

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