Myriophyllum L.

Scientific Description

Common name. Water-milfoils. Family Haloragaceae.

Habit and leaf form. Herbs. Annual, or perennial. Stem growth not conspicuously sympodial (monopodial). Hydrophytic, or helophytic (or littoral), or mesophytic; the aquatics rooted. Leaves submerged, or emergent. Heterophyllous (aquatic members with submerged leaves dissected and emergent leaves more or less entire), or not heterophyllous (when not aquatic). Leaves alternate, or opposite, or whorled; when alternate, spiral; petiolate, or sessile; non-sheathing; simple; epulvinate. Leaf blades dissected, or entire; flat, or solid; terete; oblong, or ovate, or obovate, or linear; one-veined, or pinnately veined. Leaves without stipules. Leaf blade margins entire, or dentate (or pectinate). Leaf anatomy. Hairs absent.

Reproductive type, pollination. Fertile flowers hermaphrodite, or functionally male, or functionally female, or functionally male and functionally female, or hermaphrodite, functionally male, and functionally female. Unisexual flowers present, or absent. Plants hermaphrodite, or monoecious, or dioecious, or polygamomonoecious. The unisexual flowers when monoecious, aggregated in different parts of the same inflorescence. Female flowers without staminodes. Male flowers with pistillodes, or without pistillodes. Anemophilous.

Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’; in cymes. Inflorescences flowers solitary or in small dichasia in upper axils forming spike-like inflorescence; male flowers at top of spike, female flowers (in monoecious plants) below males; pseudanthial, or not pseudanthial. Flowers pedicellate, or sessile; bracteolate, or ebracteolate; minute to small; regular; (2–)4 merous; cyclic; tetracyclic, or pentacyclic. Free hypanthium absent. Perianth with distinct calyx and corolla, or vestigial, or absent; when present, 4, or 8; 2 -whorled, or 1 -whorled; isomerous; free. Calyx present, or absent; 2–4; 1 -whorled; polysepalous; valvate; exceeded by the corolla; regular; persistent. Corolla present, or vestigial, or absent; 2–4; 1 -whorled; polypetalous; regular. Petals hooded (in male flowers). Fertile stamens present, or absent. Androecium 1–4, or 8. Androecial members free of the perianth; all equal; free of one another; 1 -whorled, or 2 -whorled. Androecium exclusively of fertile stamens. Stamens 1–4, or 8; isomerous with the perianth, or diplostemonous; alternisepalous, or oppositisepalous; filantherous (with rather large anthers). Anthers basifixed; non-versatile; dehiscing via longitudinal slits; latrorse; four locular; tetrasporangiate. Fertile gynoecium present, or absent. Gynoecium 2–4 carpelled. The pistil 2–4 celled. Gynoecium syncarpous; synovarious; inferior. Ovary plurilocular; 2–4 locular. Epigynous disk absent. Gynoecium stylate. Styles 2–4; free; apical. Placentation apical. Ovules 1 per locule; pendulous; anatropous.

Fruit and seed features. Fruit non-fleshy. Pericarp woody with solid septa. Fruit a schizocarp. Mericarps comprising nutlets. Fruit 2 locular, or 4 locular. Seeds more or less copiously endospermic. Endosperm oily. Cotyledons 2. Embryo straight.

Economic uses, etc. Used for ponds and aquaria, and important in limnological conservation.

Etymology. From the Greek for "numberless, countless" and "leaf"; refers to the numerous divisions of the leaves.