Herbs, shrubs, or subshrubs, annual (perennial in P. striatulum), homophyllous or heterophyllous, sometimes heterocarpic; roots fibrous or woody. Stems prostrate to erect, glabrous, smooth or sometimes papillous-scabridulous. Leaves cauline, alternate (opposite in P. humifusum), petiolate or sessile; ocrea with distal part persistent, often hyaline, white or silvery, 2-lobed, chartaceous, glabrous, disintegrating into fibers, or disintegrating completely; petiole base articulated with ocrea or not; blade linear, lanceolate, elliptic, ovate, or subround, margins entire. Inflorescences axillary or axillary and terminal, spikelike, or flowers solitary; peduncle absent. Pedicels present or absent. Flowers bisexual, 1-7(-10) per ocreate fascicle, base not stipelike; perianth nonaccrescent, white or greenish white to pink, campanulate to urceolate, glabrous; tepals 5, connate 3-70% of their length, petaloid or sepaloid, monomorphic or, rarely, dimorphic, the inner usually flat, the outer flat or sometimes keeled and cucullate distally, sometimes of different length than the inner; stamens 3-8 (some may be reduced to staminodes); filaments distinct, free or adnate to perianth tube, glabrous; anthers whitish yellow, pink to purple or orange-pink, elliptic to oblong; styles (2-)3, mostly spreading, distinct or connate proximally; stigmas 2-3, capitate. Achenes included or exserted, yellow-green, brown, or black, unwinged, (2-)3-gonous, glabrous. Seeds: embryo curved. x = 10.