Herbs annual [perennial], 0.3–2(–3)[–8] dm. Leaves mostly opposite, <basal soon withering, sometimes in rosettes, distal cauline sometimes alternate>, stipulate or estipulate, petiolate or sessile; blade usually 3[–5]-veined from base, margins sometimes revolute, <surfaces hairy [glabrous], hairs sometimes clustered (stellate)>. Inflorescences racemiform [helicoid, scorpioid] cymes. Pedicels present; bracts [present or] absent. Flowers chasmogamous and cleistogamous, <nodding or pendulous in bud>. Chasmogamous flowers: sepals <persistent>, 5, <outer smaller than [equaling] inner>; petals 5, yellow, sometimes purple to brown at or near bases; stamens 10–15+; <filaments distinct, outer stamens often sterile>; carpels 3; styles 0; stigmas 1, <± sessile, hemispheric [obconic]>. Cleistogamous flowers similar; petals 0; stamens 5–12. Capsules 3-valved. Seeds 6–50+ per capsule. x = 9.
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