The families of flowering plants

L. Watson and M.J. Dallwitz

Hydrostachydaceae Engl.

Alternatively Hydrostachyaceae.

Habit and leaf form. Aquatic herbs. ‘Normal’ plants. Perennial; without conspicuous aggregations of leaves; tuberous. Hydrophytic; rooted (with a holdfast and fibrous roots). Leaves submerged. Leaves simple (elongate), or compound; when divided, bipinnate, or multiply compound (variously bi- or tripinnatisect, the segments flattened, vesicular or filiform, the rachis beset with numerous small, scalelike or fringed appendages). Lamina dissected, or entire; if considered simple/ dissected, much-divided. Leaves ligulate (if the ‘stipules’ be so interpreted), or eligulate; inconspicuously stipulate, or exstipulate (if considered ‘ligulate’). Stipules if recognised as such, intrapetiolar; concrescent.

Leaf anatomy. Stomata absent. The mesophyll containing crystals. The crystals druses. Foliar vessels absent.

Axial (stem, wood) anatomy. Secondary thickening absent (the vascular system much reduced). The axial xylem without vessels.

Root anatomy. Root xylem without vessels.

Reproductive type, pollination. Plants dioecious (usually), or monoecious.

Inflorescence, floral, fruit and seed morphology. Flowers densely aggregated in ‘inflorescences’; in spikes. The ultimate inflorescence units racemose. Inflorescences scapiflorous. Flowers bracteate (the bracts accrescent); small (inconspicuous). Hypogynous disk absent.

Perianth absent.

Androecium in the male flowers, 1; exclusively of fertile stamens. Stamens 1; shortly filantherous. Anthers dehiscing via longitudinal slits; extrorse; bilocular (the locules well separated); tetrasporangiate. Pollen shed in aggregates; in tetrads. Pollen grains nonaperturate; 2-celled.

Gynoecium 2 carpelled. The pistil 1 celled. Gynoecium syncarpous; synovarious to synstylovarious; superior. Ovary 1 locular. Gynoecium median; stylate. Styles 2 (long, slender, persistent); free to partially joined; apical. Placentation parietal. Ovules in the single cavity 30–100 (‘many’); anatropous; unitegmic; tenuinucellate. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells not formed (the three nuclei soon degenerating). Synergids pear-shaped. Endosperm formation cellular. Endosperm haustoria present; micropylar.

Fruit non-fleshy; dehiscent; a capsule. Capsules septicidal. Fruit many seeded. Seeds non-endospermic.

Seedling. Germination phanerocotylar. Primary root persistent.

Physiology, phytochemistry. Aluminium accumulation not found.

Geography, cytology. Paleotropical and Cape. Temperate to tropical. Southern Africa, Madagascar.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Lamiiflorae; Hydrostachyales. Cronquist’s Subclass Asteridae; Callitrichales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; Order Cornales.

Species 30. Genera 1; only genus, Hydrostachys.

General remarks. 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. • Technical details: Hydrostachys (Thonner). • Technical details: Hydrostachys (Lindley).

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: 13th March 2017.’.