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The families of flowering plants

L. Watson and M.J. Dallwitz

Callitrichaceae Link

Habit and leaf form. Mostly more or less aquatic herbs. Annual; without conspicuous aggregations of leaves, or with terminal aggregations of leaves. Hydrophytic, or helophytic; rooted. Leaves submerged, or emergent, or submerged and emergent. Heterophyllous (usually), or not heterophyllous. Leaves opposite (decussate, often becoming rosetted towards the branch tips); not gland-dotted; simple, or simple and compound (then linear and bifid when submerged); epulvinate. Lamina dissected, or entire; when dissected, finely dichotomously dissected. Leaves exstipulate.

Leaf anatomy. Stomata present (but only sporadically on submerged leaves where they are sometimes ephemeral); mainly confined to one surface (adaxial only on floating leaves), or on both surfaces. Hairs present (with terrestrial species exhibiting glands, each with a foot and an 8-celled head, and stellate hairs also found), or absent (?). Complex hairs present, or absent; in section Eucallitriche, stellate. Minor leaf veins without phloem transfer cells.

Axial (stem, wood) anatomy. Pith consisting of only two or three cells. Primary vascular tissues reduced to a feeble, axile bundle. Secondary thickening absent. The axial xylem with vessels, or without vessels.

The vessel end-walls when present, simple.

Reproductive type, pollination. Plants monoecious, or dioecious. Pollination sometimes by water.

Inflorescence, floral, fruit and seed morphology. Flowers solitary (usually), or aggregated in ‘inflorescences’ (rarely, then paired). Inflorescences and flowers axillary. Flowers commonly bracteolate (with two horn-like bracteoles); minute.

Perianth absent.

Androecium in male flowers 1; exclusively of fertile stamens. Stamens 1. Anthers dehiscing via longitudinal slits. Endothecium developing fibrous thickenings (or undifferentiated). Anther epidermis persistent. Microsporogenesis simultaneous. Tapetum glandular. Pollen grains aperturate, or nonaperturate; when aperturate, 3–4 aperturate; colpate; 3-celled.

Gynoecium in female flowers 2 carpelled. The pistil 4 celled. Gynoecium syncarpous; synovarious; superior. Ovary 2 locular (but ostensibly four, cf. Labiatae). Locules secondarily divided by ‘false septa’. Gynoecium transverse. Ovary sessile. Styles 2; free; from a depression at the top of the ovary; apical. Stigmas 2. Placentation axile to apical. Ovules 2 per locule (i.e. 1 per locellus); pendulous; epitropous; with ventral raphe; anatropous; unitegmic; tenuinucellate. Endothelium differentiated. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral (small). Synergids pear-shaped. Endosperm formation cellular. Endosperm haustoria present; chalazal and micropylar (the latter the more aggressive). Embryogeny onagrad.

Fruit non-fleshy; a schizocarp. Mericarps 4; comprising nutlets. Seeds endospermic (the endosperm fleshy). Cotyledons 2. Embryo straight.

Seedling. Germination phanerocotylar.

Physiology, phytochemistry. C3. C3 physiology recorded directly in Callitriche. Anatomy non-C4 type (Callitriche). Not cyanogenic. Alkaloids absent (one species tested). Verbascosides detected. Iridoids detected; ‘Route II’ type (decarb.). Betalains absent. Saponins/sapogenins absent. Proanthocyanidins absent. Ellagic acid absent.

Geography, cytology. Frigid zone, temperate, sub-tropical, and tropical. Cosmopolitan, except South Africa. X = 3 or 5(+).

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Lamiiflorae; Lamiales. Cronquist’s Subclass Asteridae; Callitrichales. APG III core angiosperms; core eudicot; Superorder Asteranae; lamiid. APG IV Order Lamiales (as a synonym of Plantaginaceae).

Species 25. Genera 1; only genus, Callitriche.

General remarks. If family names are to retain practical usefulness, it seems inappropriate to include Callitriche in Plantaginaceae. In terms of the descriptions compiled for this package, the genus exhibits 18 differences from them, including characters of habit, vegetative morphology and anatomy, general floral morphology, gynoecium and fruit structure, and embryology. For discussion of classificatory problems posed by Scrophulariaceae, impinging on Bignoniaceae, Buddlejaceae, Callitrichaceae, Plantaginaceae, Hippuridaceae, Lentibulariaceae, and Hydrostachydaceae, and such problem genera as Paulownia and Schlegelia, see Olmstead and Reeves (1995), who provided preliminary insights from chloroplast gene sequencing.

Illustrations. • Le Maout and Decaisne: Callitriche. • Callitriche platycarpa, and C. intermedia ssp. pedunculata (cf. C. brutia): Eng. Bot. 1272 and 1274, 1868. • Callitriche cf. brutia (as C. hamulata): Eng. Bot. 1273, 1868. • Callitriche hermaphroditica (as C. autumnalis): Eng. Bot. 1275, 1868. • Callitriche sp. (B. Ent., 1838).

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.’.