Moderate to robust, solitary or clustered, sometimes acaulescent, spiny, pleonanthic, monoecious palms. Stem very short to tall, often slender, obscured by leaf bases, or becoming bare and conspicuously ringed with leaf scars, often armed with fierce spines pointing in several directions, sometimes losing spines with age. Leaves few to numerous, regularly or irregularly pinnate, neatly abscising or marcesent; sheath splitting opposite the petiole, usually fiercely armed with large and small spines, and frequently bearing abundant indumentum; petiole very short to long, adaxially channelled near the base, distally ± flattened or angled, abaxially rounded, bearing abundant spines of varying length and dense indumentum; rachis usually much longer than the petiole, adaxially ± angled, abaxially rounded, usually densely armed and tomentose like the petiole; leaflets numerous and single-fold (or rarely few and composed of many folds), regularly arranged or grouped, and usually fanned within the groups, the whole leaf then appearing plumose, sometimes ± secondarily plicate, linear, acute, usually dark green and shiny adaxially, abaxially almost always with abundant white indumentum, the leaflet margins often conspicuously armed with short spines or bristles; transverse veinlets conspicuous or obscure. Inflorescences solitary, interfoliar, erect at first, becoming pendulous, ?protandrous, branching to 1 order; peduncle usually elongate, ± circular in cross-section, often heavily armed with spines, sometimes with spines confined only to the area just below the bract insertion, the surface frequently densely covered in indumentum; prophyll ±membranous, tubular, 2-keeled, unarmed (?always), ±included within the leaf sheaths, soon tattering; peduncular bract much exceeding the prophyll, tubular, beaked, enclosing the rachillae in bud, splitting longitudinally along the abaxial face, arched over the rachillae, persistent or eroding, usually densely tomentose and heavily armed with spines, rarely unarmed; rachis shorter than the peduncle (often very much so) often armed as the peduncle, bearing numerous spirally arranged, crowded rachillae, each subtended by a narrow triangular bract; rachillae complex, elongate, with or without an armed or unarmed basal bare portion above which bearing a single triad or 2–5 distant triads, with or without a slender bare portion distal to the triads, distal to which the rachillae appearing cylindrical, catkin-like and bearing densely packed staminate flowers in pairs or singly, immersed in pits; rachilla bracts ± acute, forming lower lip of pits, floral bracteoles very small, sometimes partially connate with rachilla bract; after anthesis, staminate portions of the rachillae eroding away, in those species with solitary triads, the fruit then borne in a close-packed ‘spike’ or head, in those with several triads the fruit more loosely arranged. Staminate flowers small, ± symmetrical; sepals 3, very small, ± triangular, ?sometimes basally connate; petals 3, much exceeding the sepals, valvate, boat-shaped, connate basally and adnate to the receptacle; stamens (3–)6(–12, fide Wessels Boer 1965), filaments epipetalous, short, inflexed in bud, anthers ± rectangular or linear, dorsifixed, versatile, latrorse; pistillode present and trifid or absent. Pollen ellipsoidal, or oblate-triangular, usually with slight asymmetry; aperture a distal sulcus or trichotomosulcus; ectexine tectate, finely perforate-psilate or coarsely perforate, perforations closely or widely spaced or, perforate and micro-channelled and rugulate, aperture margin may be slightly finer; infratectum columellate; longest axis 41–78 µm [11/36]. Pistillate flower very much larger than the staminate; calyx urn-shaped or cup-shaped, truncate or shallowly 3-lobed, sometimes bearing numerous short spicules, usually densely tomentose; corolla not, briefly, or considerably exceeding, and similar to the calyx, or composed of 3 imbricate triangular lobes, connate basally; staminodes 6, epipetalous near the base of the corolla, connate into a low membranous ring or tooth-like; gynoecium varied in shape, trilocular, triovulate, the 3 large fleshy erect, or head-like, reflexed stigmas borne on a beak, protruding through the mouth of the corolla tube, sometimes bearing short spines and/or tomentum, ovule ?orthotropous, laterally attached. Fruit 1(–2)-seeded with apical stigmatic remains, beaked, spherical, top-shaped, prismatic, or ovoid, often brightly coloured, brown, yellowish or orange-red, calyx and corolla persistent, enlarged and irregularly splitting; epicarp spiny or unarmed, tomentose or glabrous, mesocarp relatively thin, fleshy or dry and starchy, and fibrous, sometimes with the epicarp irregularly splitting and spreading to expose the endocarp, endocarp thick, stony, with numerous flattened, black longitudinal fibres on the surface, conspicuously radiating from the 3 subterminal pores. Seed irregularly globular, basally attached, hilum circular, raphe branches anastomosing, endosperm homogeneous, usually hollow; embryo subapical, opposite one of the endocarp pores. Germination adjacent-ligular; eophyll bifid, usually bristly. Cytology: 2n = 30.
Ecologically, the genus is very varied: some species are undergrowth palms of primary lowland forest; others are light-demanding and occur in secondary forest or forest margins (e.g., riverbanks). In Surinam, Astrocaryum vulgare is particularly frequent in white sand savannah. Most species seem to be confined to the lowlands.
For local uses, see Glassman (1972) and Balick (1985). The epidermis and hypodermis of the sword leaf of Astrocaryum vulgare provide an important fibre used by Amerindians in manufacturing mats, hats, hammocks, fishing lines and nets. The mesocarp of some species is eaten by humans or fed to cattle. The kernel of A. vulgare produces a fine oil, which is excellent for eating or soap making. Fruits of A. murumuru and A. aculeatum have also been used as a source of oil, and the ‘cabbage’ of many species is utilised.