Most easily mistaken for Slender Trefoil (Trifolium micranthum) which is similarly small but Slender Trefoil has smaller leaves and all leaflets in a triplet have equal length stalks. The flowers of Slender Trefoil are also a deeper yellow and at 2-3mm long each, are also smaller than the 3-4mm of Lesser Trefoil and on a longer stalk to and with fewer in a bunch (between 2 to 6) [but can be as low as just one or as many as 10] those of the otherwise similar Lesser Trefoil.
Easily mis-identified as : Black Medick (Medicago lupulina) (when not in fruit) and with several other similar species:
Compared to Lesser Trefoil, which has (3)5 to 20 yellow flowers in a cluster, which is 3-4mm across and a hairless calyx, the flowers themselves being 3-4mm long, and sepals fused together with un-equal sepal teeth :
Large Trefoil (Trifolium aureum) has >20 golden-yellow flowers in a cluster, which are much larger at 12-20mm across (larger than all the others), the flowers themselves being 5-8mm long (longer than all the others), and much larger but still un-equal sepal teeth which are also toothed on the edges.
- Hop Trefoil (Trifolium campestre) has >25 pale-yellow flowers in a cluster, which are larger at 8-15 mm across, the flowers themselves being 4-7mm long, and larger but still un-equal sepal teeth.
- Slender Trefoil (Trifolium micranthum) has 1(2)-6(10) yellow flowers in a cluster, which are 4mm across (smaller than all the others, except for Black Medick whose cluster size can overlap); the flowers themselves being 1.5-3mm long (smaller than all the others), but with sepal teeth all equal length. But un-like all the others has fruits which are 1-2 seeded (rather than just 1-seeded of all the others)
- Black Medick (Medicago lupulina) has 'numerous' (10-50) yellow flowers in a cluster, which is 3-6mm across, the flowers themselves being 2-3mm long, the fused-together sepals being hairy, the leaves being downy with a minute 'prickle' at the tip, the big difference being in the spirally coiled fruits, which again like all but Slender Trefoil have but one seed.
Grows in bare places, rocky outcrops, and open ground dry grassland.