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Centro is a perennial herb that can reach a height of 45 cm (17.5 in). The root system can reach up to 30 cm in depth, frequently in association with Rhizobium, nitrogen-fixing bacteria. Stems grow and branch rapidly, producing a dense mass of branches and leaves on the soil. Stems do not become woody until about 18 months after planting. Leaves are trifoliate, with elliptical leaflets approximately 4 cm × 3.5 cm (1.6 in × 1.4 in), dark-green and glabrous above but whitish and densely tomentose below. Flowers are generally pale violet with darker violet veins, born in axillary racemes. Fruit is a flat, long, dark brown pod 7.5–15 cm (3.0–5.9 in) long, containing up to 20 seeds. Seeds are spherical, about 4–mm (0.16–inches) in diameter, dark brown when ripe.