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The families of flowering plants

L. Watson and M.J. Dallwitz

Zannichelliaceae Dum.

~ Potamogetonaceae.

Excluding Cymodoceaceae.

Habit and leaf form. Aquatic herbs. ‘Normal’ plants (more or less), or plants of very peculiar vegetative form; sometimes filamentous (then Chara-like). Perennial; without conspicuous aggregations of leaves; rhizomatous. Hydrophytic; non-marine (in brackish and alkaline water, not the sea); rooted. Leaves submerged. Leaves alternate (to almost opposite), or whorled (Zannichellia); usually distichous; ‘herbaceous’, or membranous; sessile; sheathing, or sheathing and non-sheathing (Zannichellia having non-sheathing, pseudowhorled blades, and also scale-leaves corresponding to sheaths). Leaf sheaths not tubular; with free margins. Leaves simple. Lamina entire; linear; one-veined, or parallel-veined (then with 3 veins); without cross-venules. Leaves ligulate. Axillary scales present (two per node).

Leaf anatomy. The mesophyll without crystals. Foliar vessels absent. Minor leaf veins without phloem transfer cells (Zannichellia).

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

Root anatomy. Root xylem without vessels.

Reproductive type, pollination. Plants monoecious (usually), or dioecious. Gynoecium of male flowers absent. Pollination by water.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in cymes. The ultimate inflorescence units cymose. Inflorescences terminal; complex cymose aggregates. Flowers small. Perigone tube absent. Hypogynous disk absent.

Perianth vestigial (in the form of a small, trilobate basal structure), or absent; 3; joined; 1 whorled.

Androecium 1 (always, ostensibly), or 2–3 (forms with 8 or 12 microsporangia perhaps representing 2 and three concrescent anthers). Androecial members coherent (if the androecium comprises more than one stamen), or free of one another. Androecium exclusively of fertile stamens. Stamens 1, or 2–3 (depending on interpretation). Anthers unilocular, or bilocular; tetrasporangiate, or multisporangiate (4, 8 or 12 sporangia, affording evidence of coalesced anthers?); appendaged (by terminal projection of the connective), or unappendaged. Microsporogenesis successive. Tapetum amoeboid. Pollen grains nonaperturate; 3-celled.

Gynoecium 1–9 carpelled. The pistil when monomerous, 1 celled. Gynoecium monomerous, or apocarpous; of one carpel, or eu-apocarpous; superior. Carpel stylate; apically stigmatic; 1 ovuled. Placentation apical. Ovules pendulous; non-arillate; orthotropous to anatropous; bitegmic; crassinucellate. Embryo-sac development Allium-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; proliferating (forming 4 or five cells), or not proliferating. Endosperm formation helobial. Embryogeny caryophyllad.

Fruit non-fleshy; an aggregate, or not an aggregate. The fruiting carpel dehiscent, or indehiscent; an achene (usually), or a follicle (Althenia). Seeds non-endospermic. Cotyledons 1. Embryo achlorophyllous (Zannichellia palustris); coiled. Testa without phytomelan; very thin.

Seedling. Germination phanerocotylar. Hypocotyl internode present (long). Seedling collar not conspicuous. Cotyledon hyperphyll elongated; assimilatory; more or less circular in t.s. Coleoptile absent. Seedling macropodous. Seedling cataphylls absent. First leaf dorsiventral. Primary root ephemeral.

Geography, cytology. Frigid zone to tropical. Lacking only from central Eurasia, central Africa and Northeast South America. X = 6–8.

Taxonomy. Subclass Monocotyledonae. Dahlgren et al. Superorder Alismatiflorae; Zosterales. APG III core angiosperms; Superorder Lilianae; non-commelinid Monocot. APG IV Order Alismatales (as a synonym of Potamogetonaceae).

Species 6. Genera 4; Althenia, Lepilaena, Pseudalthenia, Vleisia, Zannichellia.

General remarks. The comparative descriptions compiled for this package have Zannichelliaceae differing from Potamogetonaceae (q.v.) in 45 characters, representing conspicuous features of vegetative and floral morphology as well as embryology and cytology.

Illustrations. • Le Maout and Decaisne: Zannichellia palustris. • Zannichellia palustris: as Z. eu-palustris, Eng. Bot. 1425 (1869). • Zannichellia palustris: B. Ent. 718. • Zannichellia palustris, with Halodule uninervis: Codd, de Winter & Ryecroft, Flora of Southern Africa 1 (1966). • Zannichellia: fruits.

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.’.