Sensitive-pea

Chamaecrista nictitans is a slender, erect to ascending annual herb of the Fabaceae family (subfamily Caesalpinioideae), 15-60 cm tall, with a wiry taproot and finely pubescent stems that branch sparingly from the base. The leaves are alternate, even-pinnately compound, 3-7 cm long, on a short petiole bearing a small saucer- or pedicel-shaped extrafloral nectary; each leaf has 10-22 pairs of small oblong, asymmetrical leaflets 6-15 mm long and 2-4 mm wide, which fold together when touched or at nightfall — the trait giving the species its English and Latin names. Small subulate stipules persist at the leaf base. The flowers are produced singly or in small axillary clusters on short pedicels and are noticeably smaller than those of the related C. fasciculata, with five somewhat unequal bright yellow petals 6-10 mm long; ten stamens of unequal size are exposed, with four to five longer than the others. The fruit is a flat oblong linear legume 3-5 cm long and 4-6 mm wide, finely pubescent, that splits elastically at maturity to discharge several flattened dark brown angular seeds. Native to the eastern and central United States, southward through Mexico into Central and South America, on dry open soils, sandy roadsides, fields and pinewoods.