Herbs, annual (perennial in P. suffrutescens). Roots tuberous, fleshy, fibrous, or small taproots. Stems erect to prostrate, branched, fleshy or suffrutescent; trichomes in inflorescence or stem nodes absent or present, glabrous otherwise. Leaves: alternate or subopposite, congested and involucrelike immediately proximal to inflorescence; blade terete, subterete, or flattened. Inflorescences : terminal in clusters, or axillary on short branches. Flowers: sessile or subsessile, usually open only in sunshine; sepals broadly clasping at base, herbaceous to scarious, falling from top of capsule; petals ephemeral, 5-7, usually distinct, margins usually entire; stamens (4-)6-40(-100) Ovary : half inferior to inferior, plurilocular proximally to 1-locular distally, placentation free-central; style 1, short, stigmas 3-8(-18). Capsules : membranaceous, chartaceous, dehiscence circumscissile. Seeds many, brown to black or gray, reniform to cochleate; seed coat smooth or variously sculptured, granular to stellate-tuberculate or spiny. x = 4, 5, 8, 9. Species 100-125: nearly worldwide, primarily tropical and subtropical, also temperate.

PLANT: Annual or perennial herbs. STEMS: prostrate to ascending or erect. LEAVES alternate to subopposite, short-petioled or sessile, flat, cylindrical, subterete, linear or spatulate; margins entire; hairy nodes present or absent. INFLORESCENCE: typically a cyme subtended by involucral leaves with flowers crowded at the branch ends or rarely solitary. FLOWERS: perfect; sepals 2, united below, deciduous with the top of the capsule; petals mostly 5; ovary partly or wholly inferior; stamens 5 to many; stigmatic branches 2-9. CAPSULE: membranaceous, circumscissile. SEEDS: numerous, round-reniform, tuberculate, gray, brown, or black, often iridescent. NOTES: Ca. 125 spp. worldwide, mostly in the tropics and subtropics. (portula, latin for little door, referring to lid of capsule).