The families of flowering plants

L. Watson and M.J. Dallwitz

Lythraceae Jaume St.-Hil.

Including Ammanniaceae Horan., Diplodontaceae Dulac, Lagerstroemiaceae J.G. Agardh, Lawsoniaceae J.G. Agardh, Salicariaceae Juss.; excluding Punicaceae, Rhynchocalycaceae, Sonneratiaceae, Trapaceae.

Habit and leaf form. Herbs (mostly), or shrubs, or trees. Helophytic to xerophytic, or hydrophytic (in Rotala); rooted. Leaves opposite (usually), or alternate, or whorled; when alternate, spiral; petiolate to sessile; gland-dotted, or not gland-dotted; simple. Lamina entire; pinnately veined; cross-venulate. Leaves stipulate (the stipules small), or exstipulate. Lamina margins entire. Leaf development not ‘graminaceous’.

Leaf anatomy. The leaf lamina dorsiventral (usually), or bifacial (rarely, e.g., in Pemphis). Mucilaginous epidermis present, or absent. Stomata mainly confined to one surface (abaxial), or on both surfaces; anomocytic. Hairs present (with numerous kinds represented); eglandular and glandular; unicellular and multicellular (someteimes tufted or branched). Adaxial hypodermis present, or absent. The mesophyll without sclerenchymatous idioblasts; containing crystals. The crystals raphides and solitary-prismatic. Minor leaf veins without phloem transfer cells (Cuphea, Lythrum).

Axial (stem, wood) anatomy. Young stems cylindrical, or tetragonal. Secretory cavities absent. Cork cambium present; initially deep-seated. Nodes unilacunar (usually), or tri-lacunar. Primary vascular tissues in a cylinder, without separate bundles; bicollateral. Internal phloem seemingly nearly always present. Secondary thickening developing from a conventional cambial ring.

The wood ring porous to diffuse porous. The vessels small to medium; solitary, radially paired, and in radial multiples. The vessel end-walls simple. The vessels with vestured pits; without spiral thickening. The axial xylem with fibre tracheids (Heimia, Woodfordia, Pleurophora), or without fibre tracheids (mostly); with libriform fibres (mostly); at least sometimes including septate fibres, or without septate fibres. The fibres without spiral thickening. The parenchyma predominantly paratracheal. ‘Included’ phloem absent. The wood not storied. Tyloses present, or absent.

Reproductive type, pollination. Unisexual flowers absent. Plants hermaphrodite; homostylous (mostly), or heterostylous (several genera, e.g. Pemphis, Adenaria). Pollination entomophilous.

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; when aggregated, in cymes, or in panicles, or in racemes, or in verticils. The ultimate inflorescence units cymose, or racemose. Inflorescences terminal, or axillary. Flowers two bracteolate; minute to medium-sized; regular to very irregular. The floral irregularity when apparent, involving the perianth and involving the androecium. Flowers usually 4 merous, or 6 merous; cyclic, or partially acyclic. When partially non-cyclic, the androecium acyclic. Flowers when fully cyclic, usually pentacyclic. Floral receptacle developing an androphore, or with neither androphore nor gynophore. Free hypanthium present (this elongated, sometimes with a posterior spur). Hypogynous disk or a unilateral gland (Cuphea) present (around G), or absent.

Perianth with distinct calyx and corolla (usually), or sepaline (C rarely absent); (3–)8–16(–32); 2 whorled (usually), or 1 whorled; isomerous. Calyx (3–)4, or 6, or 8(–16); 1 whorled; polysepalous (sometimes?), or gamosepalous (usually, in that the ‘floral tube’ extends beyond the level of insertion of the corolla); tubular, or campanulate, or urceolate (rarely); unequal but not bilabiate, or regular; persistent; lobes valvate. Epicalyx present (commonly), or absent. Corolla (3–)4, or 6, or 8(–16); 1 whorled; polypetalous (at the mouth of the hypanthium); plicate; unequal but not bilabiate, or regular; often red, or purple, or orange. Petals clawed, or sessile.

Androecium (4–)8–16(–100) (rarely fewer than K, usually twice K or C, sometimes ‘many’). Androecial members when numerous, maturing centripetally (or the outer cycle initiating first); free of the perianth (but adnate low down on the hypanthium); all equal, or markedly unequal; free of one another; 1–3 whorled (or several). Androecium usually exclusively of fertile stamens. Stamens (4–)8–16(–35); reduced in number relative to the adjacent perianth to isomerous with the perianth to polystemonous; alternisepalous, or oppositisepalous; inflexed in bud (usually), or erect in bud. Anthers dorsifixed; versatile (mostly), or non-versatile (Crenea, Pleurophora); dehiscing via longitudinal slits; introrse; tetrasporangiate. Endothecium developing fibrous thickenings. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral. Anther wall initially with more than one middle layer; of the ‘dicot’ type. Tapetum glandular. Pollen grains aperturate; 3 aperturate (usually), or 9 aperturate; colpate, or colporate, or colpate and colporate (sometimes with pseudocolpi intervening, sometimes syncolpate); 2-celled (in 6 genera).

Gynoecium 2–4(–6) carpelled. The pistil 1 celled, or 2–4(–6) celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary 1 locular (rarely), or 2–4(–6) locular (but sometimes with the septa not reaching the top); sessile to stipitate (stipitate in Lagerstroemia, Diplusodon, Peplis etc.). Gynoecium stylate (mostly), or non-stylate to stylate. Styles 1; apical. Stigmas 1; usually capitate; wet type (known only in Lagerstroemia), or dry type (recorded in 13 genera); papillate; Group II type. Placentation rarely (i.e.when unilocular), parietal; usually axile. Ovules (1–)5–50 per locule (usually ‘many’); ascending, or horizontal; non-arillate; anatropous; bitegmic; crassinucellate. Outer integument contributing to the micropyle. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral. Synergids hooked. Hypostase usually present. Endosperm formation nuclear. Embryogeny onagrad.

Fruit non-fleshy; dehiscent, or indehiscent; a capsule, or capsular-indehiscent. Capsules septicidal, or loculicidal, or circumscissile, or splitting irregularly. Seeds non-endospermic; winged (in a few genera, the wing unilateral in Lagerstroemia, encircling in Lafoensia, Galpinia etc.), or wingless (in most genera). Cotyledons 2; flat (usually), or folded (Lagerstroemia). Embryo achlorophyllous (2/3); straight.

Seedling. Germination phanerocotylar.

Physiology, phytochemistry. C3. C3 physiology recorded directly in Ammannia, Lythrum. Anatomy non-C4 type (Decodon). Sugars transported as oligosaccharides + sucrose (Lagerstroemia). Not cyanogenic. Alkaloids present, or absent (mostly). Anthraquinones detected (Woodfordia); polyacetate derived. Iridoids not detected. Saponins/sapogenins absent. Proanthocyanidins absent. Flavonols present (Cuphea), or absent; when present, kaempferol and quercetin. Ellagic acid present (4 species, 4 genera). Aluminium accumulation not found.

Geography, cytology. Temperate to tropical. Cosmopolitan, except frigid regions. X = 5–11.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Myrtiflorae; Myrtales. Cronquist’s Subclass Rosidae; Myrtales. APG III core angiosperms; core eudicot; Superorder Rosanae; malvid. APG IV Order Myrtales.

Species 580. Genera 28; Adenaria, Ammannia, Capuronia, Crenea, Cuphea, Decodon, Didiplis, Diplusodon, Galpinia, Ginoria, Haitia, Heimia, Hionanthera, Koehneria, Lafoensia, Lagerstroemia, Lawsonia, Lourtella, Lythrum, Nesaea, Pehria, Pemphis, Peplis, Physocalymma, Pleurophora, Rotala, Tetrataxis, Woodfordia.

Illustrations. • Adenaria floribunda, as A. parvifolia: Hook. Ic. Pl. 2 (1837). • Le Maout and Decaisne: Lythrum. • Lythrum salicaria: Lindley. • Nesaea floribunda: Thonner. • Ammannia senegalensis, as Ameletia floribunda: Hook. Ic. Pl. 9 (1852). • Cuphea llavea: Bot. Reg. 1386, 1830. • Heimia salicifolia var. grandiflora: Bot. Reg. 60, 1841. • Lagerstroemia indica: R. Wight (1840). • Lythrum junceum, as L. graefferi: Bot. Mag. 106 (1880). • Lythrum salicaria (B. Ent.). • Rotala wallichii, as Hydrolythrum: Hook. Ic. Pl. 11 (1867–71). • Leaf hairs of Cuphea and Woodfordia (Solereder, 1809).

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 5th March 2018.’.