Perennial herbs with a thick rhizome. Leaves radical, narrow, with parallel lateral nerves. Inflorescence scapose, capitate or unilaterally spicate. Flowers hermaphrodite, actinomorphic. Perianth double, the outer hyaline, lobes chaffy, rigid, imbricate, inner tubular, hyaline, lobes ovate, spreading, broadly imbricate. Stamens 6, inserted in the tube; anthers basifixed, 4-locular, loculi confluent at the top and opening by 1 or 2 pores or by a terminal cleft. Ovary superior, perfectly or imperfectly 3-locular; style simple. Ovules few to solitary, basal or axile. Fruit a capsule, opening by 3 valves septate in the middle. Seeds with copious mealy endosperm.
Terrestrial, epiphytic, or amphibic perennial herbs with an erect or prostrate rhizome. Leaves unifacial to bifacial, condensed on a short stem, with an open asymmetrical conduplicate sheath; distichously or spirodistichously arranged; rarely petiolate, the petiole and the leaf blade occasionally bearing short spines; ligules rarely present. Inflorescences solitary or crowded, axillary or terminal, on leafless scapes, often subtended by 2 or more spathaceous bracts, globose or flat; the spikelets composing the inflorescences bearing numerous coriaceous bracts and a terminal flower; inflorescences that have an indeterminate main axis and lateral cymose units are more common than those with a determinate main axis and cymose lateral units (Monotremeae); flowers trimerous, hypogynous, perfect, and actinomorphic or slightly zygomorphic; sepals 3; petals 3, occasionally spotted; stamens 3 + 3, tetrasporangiate, connate at the base or adnate to the corolla tube, basifixed; anthers sometimes bearing terminal appendages, dehiscing by 4, 2, or 1 apical or subapically lateral pores, extrose or latrose; ovary syncarpous, superior, 3-locular or 1-locular by abortion; style 1, erect; stigma capitate, often minutely ciliate; ovules 1-8 per locule, anatropous, bitegmic, and crassinucellate; placentation axile or basal; fruit a septicidal capsule; seeds globose, prismatic, or oblong, occasionally bearing appendages; endosperm containing abundant starch; embryo lenticular, at micropylar end with flat surface appressed to endosperm; mechanical tissue of seed coat derived from both integuments.
A basically neotropical family of 16 genera and about 80 species, with the greatest diversity in the Guayana region and with one disjunct genus in W Africa.
Rapateaceae are most often found on oligotrophic white sand substrates or bogs, but occur also in a variety of other habitats such as forest understory, shrublands, seasonally flooded savannas, and open rock and bog formations (Fig. 100). Exclusively highland taxa occur in bogs and on sandstone and granitic substrates, where they have a narrow distribution or are endemics to particular table mountian (tepui) summits; e.g., in the Saxofridericieae, Phelpsiella, Amphiphyllum, and Marahuacaea are each endemic to a single tepui. The majority of the Rapateoideae occupy lowlands where they have probably diversified more recently. Characteristically the African Maschalocephalus grows in white sand habitats as well.
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