The families of flowering plants.
Habit and leaf form. Herbs. Perennial; with neither basal nor terminal aggregations of leaves; rhizomatous.Stem growth conspicuously sympodial. Hydrophytic to helophytic; rooted. Leaves and stems emergent. Leaves small; whorled; (4–)6–12(–16) per whorl; sessile; simple; epulvinate. Lamina entire; linear; one-veined; without cross-venules. Leaves exstipulate. Lamina margins entire.
Leaf anatomy. Stomata present; on both surfaces. Hairs present. Complex hairs present; peltate.
Lamina isobilateral to centric.
Stem anatomy. Secondary thickening absent (the vascular system reduced to an axile strand of thin-walled tissue, with a narrow zone of phloem outside and a broader region of xylem within). Xylem with vessels, or without vessels (?).
Reproductive type, pollination. Plants hermaphrodite (usually), or monoecious (sometimes, by failure of stamens and pistils to develop in some flowers, then the pistillate flowers occur above the staminate ones), or polygamomonoecious (?). Pollination anemophilous (protogynous).
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’ (solitary in the leaf axils); in verticils; small (and inconspicuous). Free hypanthium absent.
Perianth sepaline, or vestigial to absent (greatly reduced, to a more or less entire or 2–4 lobed rim); 0, or 2–4. Calyx when detectable entire to blunt-lobed.
Androecium 1. Androecial members free of the perianth. Androecium exclusively of fertile stamens. Stamens 1 (borne on top of the ovary); filantherous (the filament slender). Anthers dorsifixed; dehiscing via longitudinal slits; bilocular; tetrasporangiate. Endothecium developing fibrous thickenings. Microsporogenesis simultaneous. Anther wall initially with one middle layer; of the ‘monocot’ type. Tapetum glandular. Pollen shed as single grains. Pollen grains aperturate; 4–6 aperturate; colpate, or colporate; 3-celled.
Gynoecium ostensibly 1 carpelled. The pistil 1 celled. Gynoecium ‘pseudo’ monomerous; ostensibly of one carpel; inferior. Carpel stylate (the style often carried between the anther lobes); apically stigmatic (the style stigmatic throughout); 1 ovuled. Placentation apical. Epigynous disk absent. Stigmas dry type; papillate; Group II type (b). Ovules pendulous; non-arillate; anatropous; unitegmic; tenuinucellate. Outer integument contributing to the micropyle. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; persistent. Synergids with filiform apparatus. Endosperm formation cellular. Embryogeny onagrad.
Fruit non-fleshy. The fruiting carpel indehiscent; an achene, or drupaceous (the exocarp thin, fleshy). Seeds thinly endospermic. Embryo well differentiated. Cotyledons 2. Embryo straight.
Physiology, biochemistry. Not cyanogenic. Alkaloids absent (one species). Iridoids detected; ‘Route II’ type (+decarb.). Verbascosides detected. Proanthocyanidins absent. Flavonols present; kaempferol (trace). Ellagic acid absent. Saponins/sapogenins absent.
Geography, cytology. Holarctic, Paleotropical, Neotropical, Cape, Australian, and Antarctic. Frigid zone and temperate. Cosmopolitan. X = 8, 16(?).
Taxonomy.Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Lamiiflorae; Hippuridales. Cronquist’s Subclass Asteridae; Callitrichales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; lamiid; Order Lamiales (as a synonym of Plantaginaceae).
Species 1–3. Genera 1; Hippuris.
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