Twining, creeping, or erect perennials or juicy unbranched herbs of monopodial growth; tuberous roots or rhizome sometimes with scale leaves (Pentastemona); plants glabrous, glabrescent, or with unicellular or uniseriate hairs. Leaves distichous, alternate, opposite, or verticillate, occasionally dispersed (in Pentastemona, with leaves that are fleshy, but papyraceous when dry), petiolate and sometimes sheathing at the base; blade +/- ovate, with entire margin; longitudinal or arching basal and suprabasal veins interconnected by fine transversal veinlets. Inflorescences axillary, uniflorous or in lax few-flowered cymose clusters, or several in subumbellate clusters,or in simple or compound racemes, often withering with the whole leafy stem; flowers and bracts sometimes dotted with raphides; flowers pedicelled and usually articulated from pedicel, with pericladium, dimerous or 5-merous , hermaphrodite or functionally wholly or partly unisexual with some dimorphism; tepals 2 + 2 or in 1 whorl, free or partly united or basally connate, valvate or imbricate, outside sometimes papillose, rarely persisting in fruit (Pentastemona); stamens 2 + 2 or in 1 whorl of 5; filaments adnate to base of tepals or apparently absent and completely united into a conspicuous fleshy ring; anthers bithecate, dehiscing introrsely or latrosely by longitudinal slits; thecae sometimes protruding into sterile appendages the tips of which may be fused; connective sometimes apically with a tepaloid appendage and a median ridge separating the thecae or grown into a complicated, swollen, disclike structure together with the top of the hypanthium and ovary, leaving 5 pouches, in each of which 2 thecae of adjacent anthers are situated; ovary superior, half-inferior or inferior, unilocular; ovules few to many, anatropous or hemi-anatropous; placenta basal (Stemona), apical or parietal and projecting inward (Pentastemona); style absent or short and inconspicuous; stigma sessile to sub-sessile, in Pentastemona broad, flattish, entire or 3- or 4-lobed. Fruit a 2-valved capsule and thin-walled or berrylike and sharply longitudinally 10-ridged (Pentastemona); seed longitudinally ridged or sometimes with a collarlike undulate arillode covering about one third of the seed (Pentastemona); with or without transparent 2-layered sarcotesta, when absent provided with elaiosome of juicy hairs originating from hilum, raphe, or micropyle; endosperm present to copious; embryo minute to small.
Most of the species of Stemona prefer a seasonal climate and occur in rather dry vegetation while Stichoneuron and Croomia are low, delicate forest dwellers. The plants of Pentastemona grow gregarious but very local as rock-dwellers in damp places in rain forest of the lowland and hill region of N and W Central Sumatra.
This article is derived from the accounts of Stemonaceae and Pentastemonaceae in Kubitzki volume 3. With kind permission from Springer Science+Business Media: This work is subject to copyright. All rights reserved, whether whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, broadcasting reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer-Verlag. Violations are liable for prosecution under German Copyright Law.All Rights Reserved