Shrubs and suffrutescent plants, unarmed, terrestrial, with raphides in the tissues, often unbranched. Leaves opposite, petiolate to subsessile, entire, with the higher-order venation not lineolate, without domatia; stipules interpetiolar, ligulate to ovate in profile, entire ot usually deeply 5--17-laciniate or -multifid, erect and pressed together in bud, persistent. Inflorescences terminal and/or pseudoaxillary, subcapitate to cymose, 1--several-flowered, subsessile to pedunculate, bracteate with bracts entire to multifid. Flowers sessile to shortly pedicellate, bisexual, homostylous, apparently protandrous, small to medium-sized, perhaps fragrant, perhas diurnal; hypanthium ellipsoid to turbinate; calyx limb well developed, (4)5-lobed, with lobes sometimes unequal and/or spatulate but without calycophylls; corolla salverform with well developed tube, white, glabrous inside, lobes 5, triangular, valvate in bud, without appendages or with surfaces and/or margins markedly verrucose; stamens 5, inserted in upper part of corolla tube, anthers narrowly oblong, dorsifixed near base, dehiscent by linear slits, included, sometimes with connective prolonged into linear apical appendage; ovary fully or partially 2-locular, with ovules numerous in each locule, in fully 2-locular ovaries with axile peltate placenta and in incompletely 2-locular ovaries with basal placentas, stigmas 2, linear to ellipsoid, included to partially exserted. Fruit baccate but apparently indehiscent, subglobose to ellipsoid, fleshy, perhaps green, with calyx limb persistent and frequently enlarged; seeds numerous, small (0.3--0.5 mm), angled to subglobose, reticulated.

Key to Species of Amphidasya

1. Stipules entire; erect branched shrubs.....Amphidasya venezuelensis

1'. Stipules laciniate; herbs, low sparsely branched shrubs, or unbranched shrubs.

    2. Calyx lobes 4, stipitate, with an ovate to lanceolate limb on a narrow stipe-like basal portion.....Amphidasya spathulata

    2'. Calyx lobes 5, narrowly triangular to triangular, elliptic, oblanceolate, ligulate, or obovate, without a stipe-like basal portion.

        3. Leaf blades oblanceolate to obovate, widest above the middle, at base acute to acuminate.

            4. Calyx lobes at anthesis 15-24 mm long, linear to narrowly oblanceolate, acute to acuminate; stipules with the stipule body (i.e., the undivided basal portion) 2-12 mm long...Amphidasya ambigua

            4. Calyx lobes at anthesis 6-15 mm long, narrowly triangular to narrowly oblanceolate, narrowly ligulate, obovate, or spathulate; stipules with the stipule body 1-4 mm long.

                5. Inflorescences subsessile; calyx lobes acute to acuminate.....Amphidasya longicalycina

                5'. Inflorescences with peduncles 0.5-2 cm long; calyx lobes acute to obtuse, rounded, or truncate.

                    6. Stipule lobes 5-13 mm long; western Colombia to Amazonian Peru....Amphidasya colombiana

                    6'. Stipule lobes 4-5.5 mm long; Sierra de la Neblina, Venezuela....Amphidasya neblinae

        3'. Leaf blades elliptic, elliptic-oblanceolate, narrowly elliptic, elliptic-oblong, or ovate, widest variously below, at, or just above the middle, at base truncate, obtuse, rounded, cuneate, or acute but not or only shortly acuminate along petiole;

            7. Corolla tube ca. 8 mm long; stipules with the stipule body (i.e., the undivided basal portion) 0.5-2 mm long and with 1-3 lobes....Amphidasya amethystinae

            7'. Corolla tube 11-42 mm long (but unknown in Amphidasya brevidentata); stipules with the stipule body 1-15 mm long and with 4-11 lobes.

                8. Stipules with the stipule body 2 or more times as long as the lobes....Amphidasya brevidentata

                8'. Stipules with the stipule body about half as long or less as the lobes.

                    9. Corolla tube 11-15 mm long; calyx lobes at anthesis oblanceolate, obovate, or spathulate, 0.8-4 mm wide.

                        10. Leaves with secondary veins 10-15 pairs; corolla tube 13-15 mm long....Amphidasya colombiana

                        10'. Leaves with secondary veins 16-18 pairs; corolla tube 11-11.5 mm long....Amphidasya intermedia

                    9'. Corolla tube 25-42 mm long; calyx lobes at anthesis linear to narrowly elliptic, narrowly ligulate, narrowly triangular, or oblanceolate, 0.5-15 mm wide.

                        11. Calyx lobes at anthesis 9-10 mm long; corolla lobes smooth on the margins and adaxial surfaces.....Amphidasya umbrosa

                        11'. Calyx lobes at anthesis 9-19 mm long; corolla lobes markedly verruculose on the margins and adaxial surfaces, sometimes these projections giving the appearance of laciniate.

                            12. Corolla tube 36-40 mm long; eastern and central Panama.....Amphidasya panamensis

                            12'. Corolla tube 25-30 mm long; northwestern South America.

                                13. Corolla in bud acute to acuminate at apex; leaves with secondary veins 10-16 pairs.....Amphidasya bullata

                                13. Corolla in bud truncate at apex; leaves with secondary veins 22-30 pairs.....Amphidasya elegans