Habit and leaf form. Herbs (often coarse). Perennial; with a basal aggregation of leaves; rhizomatous (mostly with simple stems). Helophytic, or mesophytic. Leaves alternate; tristichous; flat to folded (usually V-shaped), or terete; petiolate (e.g.Saxofredericia), or subsessile; sheathing. Leaf sheaths not tubular; with free margins. Leaves 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; parallel-veined.
General anatomy. Plants with silica bodies. Accumulated starch other than exclusively ‘pteridophyte type’.
Leaf anatomy. Epidermis containing silica bodies (in the form of rounded druses). Stomata present; mainly confined to one surface (abaxial, not sunken, not organized into regular files); paracytic (Dahlgren et al.1985). Guard-cells ‘grass type’ (Dahlgren et al. 1985).
Lamina dorsiventral, or centric. The mesophyll not containing mucilage cells; without calcium oxalate crystals. Vessels mostly absent.
Stem anatomy. Secondary thickening absent. Xylem with vessels. 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 (in Maschalocephalus, where the scape is greatly reduced); axillary; each comprising a capitate to unilaterally racemose cluster of (1–)many 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; spatheate. Flowers (multi-) bracteate; regular to somewhat irregular; 3 merous; cyclic; pentacyclic. Perigone tube absent. 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. 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, biochemistry. Aluminium accumulation demonstrated (the most notable Monocots in this respect).
Geography, cytology. Paleotropical (Maschalocephalus only), or Neotropical. Tropical. Eastern tropical South America, West tropical Africa. 2n = 22 in Maschalocephalus.
Taxonomy. Subclass Monocotyledonae. Dahlgren et al. Superorder Commeliniflorae; Commelinales. APG 3 core angiosperms; Superorder Lilianae; commelinid Monocot; Order Poales.
Species 80. Genera 17; Amphiphyllum, Cephalostemon, Duckea, Epidryos, Guacamaya, Kunhardtia, Marahuacaea, Maschalocephalus, Monotrema, Phelpsiella, Potarophytum, Rapatea, Saxofridericia, Schoenocephalum, Spathanthus, Stegolepis, Windsorina.