| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### Hippuridaceae Link.

~ Plantaginaceae.

Habit and leaf form. Herbs. Perennial; without conspicuous aggregations of leaves; rhizomatous. Stem growth conspicuously sympodial. Hydrophytic to helophytic; rooted. Leaves and stems emergent. Leaves small; whorled; (4–)6–12(–16) per whorl; sessile; simple; epulvinate. Lamina entire; linear; one-veined; without cross-venules. Leaves exstipulate. Lamina margins entire.

Leaf anatomy. The leaf lamina bifacial (isobilateral), or centric. Stomata present; on both surfaces (or all round). Hairs present. Complex hairs present; peltate (each with a unicellular foot and multicellular head).

Axial (stem, wood) anatomy. Cork cambium absent. Secondary thickening absent (the vascular system reduced to an axile strand of thin-walled tissue, with a narrow zone of phloem outside and a broader region of xylem within, the vessels with spiral or reticulate thickening). The axial xylem with vessels, or without vessels (?).

Reproductive type, pollination. Unisexual flowers present, or absent. Plants hermaphrodite (usually), or monoecious (sometimes, by failure of stamens and pistils to develop in some flowers, then the pistillate flowers occur above the staminate ones), or polygamomonoecious (?). Pollination anemophilous (protogynous).

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’ (solitary in the leaf axils); in verticils; small (and inconspicuous). Free hypanthium absent.

Perianth sepaline, or vestigial to absent (greatly reduced, to a more or less entire or 2–4 lobed rim); 0, or 2–4. Calyx when detectable entire to blunt-lobed.

Androecium 1. Androecial members free of the perianth. Androecium exclusively of fertile stamens. Stamens 1 (borne on top of the ovary); filantherous (the filament slender). Anthers dorsifixed; dehiscing via longitudinal slits; bilocular; tetrasporangiate. Endothecium developing fibrous thickenings. Microsporogenesis simultaneous. Anther wall initially with one middle layer; of the ‘monocot’ type. Tapetum glandular. Pollen shed as single grains. Pollen grains aperturate; 4–6 aperturate; colpate, or colporate; 3-celled.

Gynoecium ostensibly 1 carpelled. The pistil 1 celled. Gynoecium ‘pseudo’ monomerous; ostensibly of one carpel; inferior. Carpel stylate (the style often carried between the anther lobes); apically stigmatic (the style stigmatic throughout); 1 ovuled. Placentation apical. Epigynous disk absent. Stigmas dry type; papillate; Group II type (b). Ovules pendulous; non-arillate; anatropous; unitegmic; tenuinucellate. Outer integument contributing to the micropyle. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; persistent. Synergids with filiform apparatus. Endosperm formation cellular. Embryogeny onagrad.

Fruit non-fleshy. The fruiting carpel indehiscent; an achene, or drupaceous (the exocarp thin, fleshy). Seeds thinly endospermic. Embryo well differentiated. Cotyledons 2. Embryo straight.

Seedling. Germination phanerocotylar.

Physiology, phytochemistry. Not cyanogenic. Alkaloids absent (one species). Verbascosides detected. Iridoids detected; ‘Route II’ type (+decarb.). Saponins/sapogenins absent. Proanthocyanidins absent. Flavonols present; kaempferol (trace). Ellagic acid absent.

Geography, cytology. Holarctic, Paleotropical, Neotropical, Cape, Australian, and Antarctic. Frigid zone and temperate. Cosmopolitan. X = 8, 16(?).

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

Species 1–3. Genera 1; Hippuris.

General remarks. Differing conspicuously from Plantaginaceae in numerous vegetative and floral morphological features (whorled leaves, reduced perianth, monomerous, inferior gynoecium, etc.), also in recorded data on pollen morphology and stigma details.

Illustrations. • Le Maout and Decaisne: Hippuris vulgaris. • Hippuris vulgaris: anatomical details (Goebel). • Hippuris vulgaris: Eng. Bot. 516 (1865). • Hippuris vulgaris (B. Ent.).

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: 8th June 2026. delta-intkey.com’.

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