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Shrubs, subshrubs, or perennial herbs, with cystoliths, usually spiny. Leaves opposite, petiolate. Inflorescences axillary cymes (sometimes secund or reduced to dense clusters), terminal spikes, or flowers solitary; bracts present or absent; bracteoles 2, sometimes becoming spinose. Calyx deeply 4-lobed; outer 2 lobes larger [anterior lobe sometimes 2-cleft]; inner 2 lobes smaller. Corolla funnel-shaped, usually large; limb 5-lobed (usually with upper lip appearing 4-lobed); lobes subequal, quincuncial in bud. Stamens [2 or]4 and didynamous, one pair usually greatly reduced and/or sterile; anthers 2-thecous; thecae ± equal in size, equally inserted, lacking basal appendages; staminodes 1 or 3, sometimes bearing very small anthers. Ovary with 2 ovules per locule; stigma 2-cleft or entire. Capsule substipitate or lacking a distinct basal stalk, subellipsoid to ovoid, 2-4-seeded; retinacula present. Seeds discoid, pubescent with appressed hygroscopic trichomes.
Shrubs or herbs, erect, sometimes spiny. Leaves opposite, petiolate to nearly sessile, the cystoliths generally prominent and dense on both the surfaces, the margins entire. Inflorescence axillary or dense terminal bracted spikes. Flowers with the calyx deeply 4-lobed, the lobes unequal; corolla 5-merous, the broad, spreading lobes mostly subequal, bilabiate in Panama; stamens 4, didynamous, adnate to the base of the corolla tube, generally all stamens perfect, but American species with only 2 perfect stamens and 2 staminodes. Capsules ovate to oblong, flattened, with 2 seeds per locule; seeds flattened, ovate to suborbicular.
