- Family: Pea Family – Fabaceae (Leguminosae)
- Growing form: Perennial herb. Rhizomatous.
- Height: 20–45 cm (8–18 in.). Stem ascending–erect, curved (zig-zagged), sparsely haired.
- Flower: Corolla zygomorphic, purple, 12–20 mm (0.48–0.8 in.) long, fused at base. Petals 5; the upstanding the ‘standard’, the lateral two the ‘wings’, the lower two united to form the ‘keel’, overall shape of corolla being butterfly-like. Calyx 5-lobed, calyx-tube glabrous, lobes hairy, lowest lobe longer than others. Stamens 10. A single carpel. Inflorescence a long-stalked, densely globose head.
- Leaves: Alternate, stalked, stipulate. Blade with 3 leaflets, leaflets lanceolate–elliptic, with entire–slightly toothed margins, without blotches. Stipules linearly lanceolate, long-tipped, mainly united with stalks.
- Fruit: Indehiscent pod, remains inside calyx.
- Habitat: Meadows, banks, roadsides, waste ground, broad-leaved forests, forest margins.
- Flowering time: June–August.
Zigzag clover is native to Finland. It demands light and heat and doesn’t survive in gloomy backwoods, and it also finds the going pretty tough in open places where it has to compete with meadow species. It thrives well in hillside forests as well as areas that have been storm-damaged and other areas that are open due to e.g. logging or fires. It seems to have exploited human activity such as forest clearing and the moderate change of hillside forest into grazing land, and it has spread from its original habitats to become a companion of people. Although zigzag clover looks very much like the king of useful plants red clover, it has never itself been a significant fodder crop.
Most clovers have to be cross-pollinated for the germinating seeds to sprout. Any old insect isn’t good enough to do the job, however: clover flowers are long-tubed and fused at the base so only quite large bumble bees, honey bees and certain butterflies have a proboscis long enough to reach the nectar. Sometimes a small hole can be found at the bottom of the calyx-tube. This is a sign of a visit from an insect with a short proboscis that has broken in to the nectar store – it goes without saying that this does nothing to pollinate the flower.
Zigzag clover differs from red clover (T. pratense) in that the former’s leaflets are longer, narrower and usually without the light-coloured V-shape that is typical of red clover. Additionally, red clover’s inflorescence is stalkless, slightly denser, and its corolla is a lighter colour, almost white.