| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### Rapateaceae Dum.

Habit and leaf form. Herbs (often coarse). Perennial; with a basal aggregation of leaves; mostly with simple stems, creeping rhizomatous. Helophytic, or mesophytic. Leaves alternate; spiral, or distichous (mostly, flabellate), or tristichous; flat to folded (usually V-shaped), or terete; petiolate (e.g.Saxofredericia), or subsessile to sessile (usually); sheathing. Leaf sheaths usually asymmetrically flattened, not tubular; with free margins. Leaves with blades borne edgewise to the stem, or with blades ‘normally orientated’; simple. Lamina twisted through 90 degrees (usually), or neither inverted nor twisted through 90 degrees (?); entire; conspicuously asymmetric to not conspicuously asymmetric (the midvein commonly displaced to one side); commonly linear to lanceolate, or oblong; parallel-veined. Leaves ligulate (rarely), or eligulate; leaf development ‘graminaceous’.

General anatomy. Plants with silica bodies.

Leaf anatomy. The leaf lamina dorsiventral, or bifacial, or centric (?). Epidermis containing silica bodies (in the form of rounded druses). Stomata present; mainly confined to one surface (usually - abaxial, neither sunken nor organized into regular files), or on both surfaces (?); paracytic (Dahlgren et al.1985). Guard-cells ‘grass type’ (Dahlgren et al. 1985). The mesophyll not containing mucilage cells; without crystals. Foliar vessels mostly absent.

Axial (stem, wood) anatomy. Secondary thickening absent.

The vessel end-walls scalariform, or simple.

Root anatomy. Root xylem with vessels; vessel end-walls scalariform, or simple (mostly scalariform).

Reproductive type, pollination. Unisexual flowers absent. Plants hermaphrodite. Floral nectaries absent (Cronquist 1981). Pollination entomophilous.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in ‘spikelets’. Inflorescences scapiflorous (usually, the scape usually rather long), or not scapiflorous (e.g., in Maschalocephalus, where the scape is greatly reduced); axillary; each comprising a capitate to unilaterally racemose cluster of (1–)many bracteate, pedunculate or sessile spikelets, borne on a short, compact inflorescence receptacle; with involucral bracts (usually, there being (1–)2 often large, basally broad, sometimes fused spathal leaves, rarely completely enclosing the infloresence); more or less pseudanthial, or not pseudanthial; spatheate. Flowers (multi-) bracteate; regular to somewhat irregular; 3 merous; cyclic; pentacyclic. Perigone tube present to absent (short). Hypogynous disk absent.

Perianth with distinct calyx and corolla; 6; 2 whorled; isomerous; sepaloid and petaloid; without spots (usually), or spotted (very rarely); different in the two whorls. Calyx 3; 1 whorled; polysepalous, or gamosepalous (chaffy, indurated at the base, sometimes basally connate); regular; imbricate. Corolla 3 (ephemeral, fragile); 1 whorled; polypetalous (rarely), or gamopetalous (usually tubular below); imbricate; regular; for the most part yellow, or red; plain, or with contrasting markings (sometimes with brown or violet spots).

Androecium 6. Androecial members free of the perianth, or adnate; free of one another, or coherent (the filaments often connate at the base); 2 whorled (3+3). Androecium exclusively of fertile stamens. Stamens 6; inserted when epipetalous, near the base of the corolla tube; diplostemonous; oppositisepalous; both alternating with and opposite the corolla members; alterniperianthial; filantherous (the filaments short, the anthers usually very long but shorter than the corolla). Anthers (sub-) basifixed; non-versatile; dehiscing via pores to dehiscing via short slits (by one, two or four openings); introrse; unilocular (occasionally), or bilocular; bisporangiate (when unilocular), or tetrasporangiate; shortly appendaged (usually), or unappendaged (Schoenocephalium). The anther appendages apical (by short connective extension). Endothecium developing fibrous thickenings. The endothecial thickenings spiral. Microsporogenesis probably simultaneous. The initial microspore tetrads tetrahedral. Tapetum glandular. Pollen shed as single grains. Pollen grains aperturate; 1 aperturate, or 2 aperturate; sulcate, or sulculate, or zoniaperturate; probably 2-celled.

Gynoecium 3 carpelled. Carpels isomerous with the perianth. The pistil 1 celled, or 3 celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary 3 locular (but the partitions sometimes incomplete near the top, and only one of the locules fertile in Spathanthus). Gynoecium stylate. Styles 1; apical. Stigmas 1; simple. Placentation axile, or basal to axile (when few-ovuled). Ovules 1–2 per locule, or 5–50 per locule (to ‘many’); ascending; anatropous; crassinucellate. Embryo-sac development Polygonum-type. Endosperm formation nuclear.

Fruit non-fleshy; dehiscent; a capsule. Capsules loculicidal. Seeds copiously endospermic. Endosperm not oily (mealy, starchy). Seeds winged, or wingless. Seeds with starch. Embryo rudimentary at the time of seed release (small, lenticular, situated at the micropylar end). Testa without phytomelan.

Seedling. Coleoptile absent.

Physiology, phytochemistry. Accumulated starch other than exclusively ‘pteridophyte type’. Aluminium accumulation demonstrated (the most notable of Monocots in this respect).

Geography, cytology. Paleotropical (Maschalocephalus only), Neotropical. Tropical. Eastern tropical South America, West tropical Africa. 2n = 22 in Maschalocephalus.

Taxonomy. Subclass Monocotyledonae. Dahlgren et al. Superorder Commeliniflorae; Commelinales. APG III core angiosperms; Superorder Lilianae; commelinid Monocot. APG IV Order Poales.

Species about 80. Genera 17; Amphiphyllum, Cephalostemon, Duckea, Epidryos, Guacamaya, Kunhardtia, Marahuacaea, Maschalocephalus, Monotrema, Phelpsiella, Potarophytum, Rapatea, Saxofridericia, Schoenocephalium, Spathanthus, Stegolepis, Windsorina.

Illustrations. • Duckea junciformis, Monotrema bracteatum and M. affine: Mem. New York Bot. Gard. 10 (1958). • Maschalocephalus dinklagei: Engler & Drude, Die Vegetation der Erde 9 (1908). • Rapatea paludosa, R. pycnocephala, Spathanthus unilateralis, Cephalostemon riedelianus: Engler, Nat. Pflanzenfam, 2 (1889). • Rapatea paludosa: Baillon, Histoire des Plantes 13 (1895). • Rapatea pycnocephala and R. paludosa: Fl. Brasiliensis III (1842–1871). • Schoenocephalium arthrophyllym and Spathanthus unilateralis: Fl. Brasiliensis III (1842–1871). • Schoenocephalium martianum: Engler, Nat. Pflanzenfam, 2 (1889). • Spathanthus unilateralis Baillon, Histoire des Plantes 13 (1895). • Stegolepis humilis: Steyermark, Ann. Miss. Bot. Gard. 74 (1987).

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 8th June 2026. delta-intkey.com’.

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