Lythrum L.

Scientific Description

Common name. Loosestrifes. Family Lythraceae.

Habit and leaf form. Sub- shrubs, or herbs. Herbs annual, or perennial. Young stems cylindrical, or tetragonal. Helophytic to xerophytic. Leaves alternate, or opposite, or whorled; when alternate, spiral; 3 per whorl; petiolate to subsessile, or sessile; gland-dotted, or not gland-dotted; simple. Leaf blades entire; elliptic, or oblong, or ovate, or linear; pinnately veined; cross-venulate; auriculate at the base, or attenuate at the base, or rounded at the base (or stem-clasping or obtuse). Leaves without stipules. Leaf blade margins entire. Leaves without a persistent basal meristem. Stem anatomy. Secondary thickening developing from a conventional cambial ring.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Plants homostylous (di- or trimorphic). Entomophilous.

Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’; in cymes, or in fascicles (or clusters). The terminal inflorescence unit cymose, or racemose. Inflorescences axillary. Flowers pedicellate, or sessile; bracteolate; minute to medium-sized; regular; 4 merous, or 6 merous; pentacyclic. Floral receptacle developing an androphore, or with neither androphore nor gynophore. Free hypanthium present; narrowly campanulate, or tubular; ribbed; sinus appendages present, elongate. Hypogynous disk present, or absent. Perianth with distinct calyx and corolla; (3–)8–16(–32); 2 -whorled; isomerous. Calyx present; 4–6; 1 -whorled; gamosepalous; blunt-lobed; lobes valvate; tubular, or campanulate, or urceolate; unequal but not bilabiate, or regular; persistent. Calyx lobes triangular (to deltate). Epicalyx present, or absent. Corolla present, or absent (rarely); 4–6; 1 -whorled; polypetalous; plicate; unequal but not bilabiate, or regular; pink, or purple, or blue. Petals ovate, or obovate; sessile. Androecial members definite in number. Androecium 2–12. Androecial sequence determinable, or not determinable. Androecial members when determinable, maturing centripetally; adnate (to the hypanthium, low down); markedly unequal (dimorphic); free of one another; 1–3 -whorled (or several). Androecium exclusively of fertile stamens. Stamens 2–12; attached inside the hypanthium; all more or less similar in shape; reduced in number relative to the adjacent perianth to isomerous with the perianth to polystemonous; oppositisepalous; inflexed in bud, or erect in bud. Anthers dorsifixed; versatile; dehiscing via longitudinal slits; introrse; tetrasporangiate. Gynoecium 2 carpelled. The pistil 2 celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary plurilocular; 2 locular; sessile to stipitate. Gynoecium stylate. Styles 1; apical. Stigmas 1; capitate. Placentation axile. Ovules (1–)5–50 per locule; ascending, or horizontal; non-arillate; anatropous.

Fruit and seed features. Fruit non-fleshy; dehiscent; a capsule. Capsules septicidal. Seeds non-endospermic; wingless. Cotyledons 2. Embryo straight.

Etymology. From the Greek for "black blood"; generally thought to refer to the purple colour of the flowers of some species, but it has been suggested that it refers to some styptic property of the plant.