Saururaceae A. Rich.
Habit and leaf form. Herbs (with articulated stems); bearing essential oils. Biennial; with neither basal nor terminal aggregations of leaves; rhizomatous. Helophytic, or mesophytic. Leaves alternate; spiral to distichous; petiolate; aromatic; simple. Lamina entire; mostly oblong, or ovate; pinnately veined, or palmately veined; cross-venulate; cordate, or rounded at the base. Leaves stipulate. Stipules intrapetiolar (and adnate to the petiole). Lamina margins entire.
General anatomy. Accumulated starch other than exclusively ‘pteridophyte type’.
Leaf anatomy. Stomata present; cyclocytic.
Adaxial hypodermis present. Lamina dorsiventral. The mesophyll with spherical etherial oil cells; containing calcium oxalate crystals. The mesophyll crystals druses. Minor leaf veins without phloem transfer cells (Houttuynia).
Stem anatomy. Nodes penta-lacunar, or multilacunar (with five or more traces). Primary vascular tissue comprising a ring of bundles, or in two or more rings of bundles (one ring or sometimes two, the bundles less scattered than in Piperaceae); centrifugal. Secondary thickening absent. Vessel end-walls oblique; scalariform. Sieve-tube plastids S-type.
Reproductive type, pollination. Plants hermaphrodite.
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in racemes, or in spikes. The ultimate inflorescence unit racemose. Inflorescences terminal; dense, slender, peduncled spikes or racemes; often with involucral bracts, or without involucral bracts; pseudanthial (often, the lower bracts being sometimes involucral and petaloid), or not pseudanthial. Flowers small; regular; cyclic; bi- or tricyclic. Hypogynous disk absent.
Androecium 3, or 6, or 8. Androecial members united with the gynoecium (to its whole length, or only its base), or free of the gynoecium; free of one another; 1 whorled (when 3), or 2 whorled (when six or eight, then the members alternating). Androecium exclusively of fertile stamens. Stamens 3, or 6, or 8; filantherous (with slender filaments). Anthers basifixed; non-versatile; dehiscing via longitudinal slits; extrorse to latrorse to introrse; tetrasporangiate. Endothecium developing fibrous thickenings. Anther epidermis persistent. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral, or isobilateral, or decussate. Anther wall initially with one middle layer. Tapetum glandular. Pollen shed as single grains (these small to minute). Pollen grains aperturate, or nonaperturate; when aperturate, 1 aperturate; sulcate (to faintly trichotomosulcate); 2-celled.
Gynoecium 3 carpelled, or 4(–5) carpelled. The pistil 1 celled. Gynoecium apocarpous, or syncarpous; semicarpous (the conduplicate carpels distinct above the connate base, in Saururus), or synovarious (in the other genera); superior (mostly), or inferior (Anemopsis). Carpel of Saururus incompletely closed (by virtue of the style being incompletely closed); stylate (with decurrent stigma); of Saururus (1–)2–4 ovuled. Placentation dispersed (laminar-lateral). Ovary 1 locular. Gynoecium stylate. Styles 3–4(–5); free (and not wholly closed, the stigmas decurrent); in the genera other than Saururus apical. Stigmas 3–4(–5); dry type; papillate; Group II type. Placentation parietal. Ovules in the single cavity 20–40(–50) (6–10 on each placenta); orthotropous to hemianatropous; bitegmic; tenuinucellate, or crassinucellate. Outer integument contributing to the micropyle. Embryo-sac development Polygonum-type (monosporic). Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral. Synergids hooked. Endosperm formation cellular, or helobial. Endosperm haustoria present; chalazal. Embryogeny asterad.
Fruit somewhat fleshy, or non-fleshy; an aggregate (Saururus), or not an aggregate. The fruiting carpel in Saururus indehiscent; a follicle (semisucculent). Fruit in the other genera dehiscent, or indehiscent; fleshy, a capsule, or capsular-indehiscent. Capsules when dehiscent, apically valvular. Seeds scantily endospermic. Perisperm present (copious, with clustered starch grains). Seeds with starch. Embryo rudimentary at the time of seed release (minute).
Seedling. Germination phanerocotylar.
Physiology, biochemistry. Cyanogenic (?), or not cyanogenic. Alkaloids absent (one species). Iridoids not detected. Proanthocyanidins present; cyanidin. Flavonols present; kaempferol and quercetin. Ellagic acid absent (2 genera). Saponins/sapogenins absent. C3. C3 physiology recorded directly in Saururus.
Geography, cytology. Holarctic. Temperate to tropical. Eastern Asia, Southern U.S.A. and Mexico. X = 11, 12(?).
Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Nymphaeiflorae; Piperales. Cronquist’s Subclass Magnoliidae; Piperales. APG 3 Order Piperales.
Species 7. Genera 4; Anemopsis, Gymnotheca, Houttuynia, Saururus.
• Technical details: Saururus, Gymnotheca, Houttuynia.