Herbs,-perennial, caulescent (subscapose in-P. humilis), glabrous.-Roots-sometimes tuberous, fleshy to woody.-Stems-ascending to erect, simple or branching, sometimes suffrutescent.-Leaves-alternate or subopposite, sometimes subrosulate, petiolate or sessile, articulate at base, not clasping but sometimes with auriculate, membranous to chartaceous basal enations, attachment point round; blade terete, semiterete, or narrowly planate, 1-3 (10-20 in-P. aurantiacus) mm wide, succulent (semisucculent in-P. aurantiacus, P. sediformis, and-P. spinescens).-Inflorescences-lateral and/or terminal (lateral sometimes appearing terminal due to congestion of leaves on very short stems), cymose or cymulose, not appearing secund, few- to many-flowered, or flowers solitary and axillary; peduncle very short to elongate, sometimes scapelike.-Flowers-pedicellate (sometimes subsessile or sessile in-P. parviflorus), each opening for 2-4 hours from afternoon to early evening of a single day, sometimes facultatively cleistogamous; sepals promptly deciduous after anthesis or persistent through capsule development, distinct; petals fugacious, 5 or rarely more, distinct or sometimes basally connate; stamens 4-many, distinct or with filaments basally shortly coherent in several clusters, anther 2-locular, oblong (subglobose in-P. rugospermus); gynoecium 3[-5]-carpelled, placentention free-central; style 1 [absent]; stigmas 1 or 3[-5].-Capsules-longitudinally dehiscent from apex, 3-valved; valves deciduous, erect, exocarp and endocarp not evidently differentiated and not separating.-Seeds-many, black or brown, - compressed, with or without - parallel, arcuate ridges, estrophiolate, circular-reniform, small; seed coat lustrous, smooth (corrugate-rugulose in-P. rugospermus), covered with pale white or gray, thin, dull, fleshy to chartaceous pellicle.-x-= 12.

Taxonomic tree:

Kingdom: Plantae
Phylum: Magnoliophyta
Class: Magnoliopsida
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