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The families of flowering plants

L. Watson and M.J. Dallwitz

Pontederiaceae Kunth

Including Heteranthereae (Heterantheraceae) J.G. Agardh

Habit and leaf form. Aquatic herbs. Leaves well developed, or much reduced (in Hydrothrix). Plants more or less succulent (the branches and petioles spongy and aerenchymatous); green and photosynthesizing. Annual, or perennial; with a basal aggregation of leaves, or without conspicuous aggregations of leaves. Hydrophytic; free floating, or rooted. Leaves submerged, or emergent, or floating. Leaves alternate (usually), or whorled; spiral, or distichous (usually); petiolate; sheathing. Leaf sheaths tubular. Leaves simple. Lamina entire; linear, or lanceolate, or ovate, or orbicular (or in Hydrothrix dissolved into undifferentiated filiform strands); palmately veined to parallel-veined (convergent), or pinnately veined (pinnate-parallel); without cross-venules; cordate, or attenuate to the base. Leaves ligulate, or eligulate; stipulate (if the axillary hyaline structures are so interpreted), or exstipulate. Lamina margins entire.

Leaf anatomy. Stomata present; paracytic. Hairs absent. The mesophyll containing crystals. The crystals raphides, or solitary-prismatic. Foliar vessels absent. Minor leaf veins without phloem transfer cells (Eichhornia, Pontederia).

Axial (stem, wood) anatomy. Secondary thickening absent. The axial xylem with vessels (sometimes), or without vessels.

The vessel end-walls scalariform.

Root anatomy. Root xylem with vessels; vessel end-walls scalariform.

Reproductive type, pollination. Plants hermaphrodite; homostylous, or heterostylous. Floral nectaries present, or absent (Heteranthera). Nectar secretion when occurring, from the gynoecium (via septal nectaries). Pollination usually entomophilous (apart from Heteranthera).

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; when aggregated, in racemes, or in spikes, or in panicles. The ultimate inflorescence units cymose, or racemose. Inflorescences terminal; ‘sympodial cymose pseudoracemes’, or ‘racemes, spikes, or panicles’; spatheate (often), or espatheate. Flowers small to medium-sized; regular to very irregular; when irregular, zygomorphic. The floral irregularity involving the perianth, or involving the perianth and involving the androecium. Flowers 3 merous; cyclic; pentacyclic, or tetracyclic. Perigone tube present (often), or absent.

Perianth of ‘tepals’; 6; free, or joined; 2 whorled; isomerous; petaloid; spotted (occasionally), or without spots; similar in the two whorls; white, or violet, or blue, or yellow (rarely).

Androecium (3–)6. Androecial members free of the perianth; all equal, or markedly unequal; 1 whorled, or 2 whorled (usually, 3+3). Androecium exclusively of fertile stamens, or including staminodes. Staminodes when present, 2, or 3. Stamens 1 (e.g. Hydrothrix), or 3 (Heteranthera spp.), or 6; reduced in number relative to the adjacent perianth, or isomerous with the perianth, or diplostemonous; alterniperianthial, or oppositiperianthial (when 3). Anthers basifixed (or peltate); dehiscing via longitudinal slits, or dehiscing via pores; introrse. The endothecial thickenings girdling. Microsporogenesis successive. The initial microspore tetrads isobilateral, or decussate. Tapetum glandular (usually), or amoeboid. Pollen grains aperturate; 2 aperturate, or 3 aperturate; (bi- or tri-) sulculate; 2-celled.

Gynoecium 3 carpelled. Carpels isomerous with the perianth. The pistil 1 celled, or 3 celled. Gynoecium syncarpous (but sometimes becoming pseudomonomerous); synstylovarious to eu-syncarpous; superior. Ovary 3 locular, or 1 locular (sometimes, by abortion). Gynoecium stylate. Styles 1; attenuate from the ovary; apical. Stigmas 1; 3 lobed; capitate; dry type; papillate; Group II type. Placentation when unilocular, parietal (with an intruded placenta); when trilocular, axile. Ovules in the single cavity when one-locular, 1; usually 10–50 per locule (‘many’); pendulous; non-arillate; anatropous; bitegmic; crassinucellate. Polar nuclei fusing prior to fertilization. Antipodal cells formed, or not formed (then the three nuclei degenerating early); 3; not proliferating; ephemeral, or persistent. Synergids with filiform apparatus. Endosperm haustoria present (at least in Monochoria); micropylar.

Fruit non-fleshy; dehiscent (when trilocular), or indehiscent (when pseudomonomerous); a capsule, or a nut (when pseudomonomerous/indehiscent). Capsules loculicidal. Seeds endospermic. Endosperm not oily. Seeds with starch. Embryo well differentiated. Cotyledons 1. Embryo straight. Testa without phytomelan.

Seedling. Hypocotyl internode absent. Seedling collar not conspicuous. Cotyledon hyperphyll elongated; assimilatory; dorsiventrally flattened. Coleoptile absent (but with a tubular cotyledon ‘ligule’). First leaf dorsiventral. Primary root ephemeral.

Physiology, phytochemistry. C3. C3 physiology recorded directly in Eichhornia. Anatomy non-C4 type (Pontederia). Accumulated starch other than exclusively ‘pteridophyte type’. Not cyanogenic. Alkaloids present, or absent. Saponins/sapogenins absent. Proanthocyanidins present; cyanidin, or cyanidin and delphinidin. Flavonols absent. Ellagic acid absent.

Geography, cytology. Sub-tropical to tropical. Pantropical, subtropical and warm temperate. X = 8, 14, 15.

Taxonomy. Subclass Monocotyledonae. Dahlgren et al. Superorder Bromeliiflorae; Pontederiales. APG III core angiosperms; Superorder Lilianae; commelinid Monocot. APG IV Order Commelinales.

Species 30. Genera 9; Eichhornia, Eurystemon, Heteranthera, Monochoria, Hydrothrix, Pontederia, Reussia, Scholleropsis, Zosterella.

Economic uses, etc. Some wartergarden ornamentals, including Eichhornia (water hyacinth) which is a devastating weed of warm waterways.

Illustrations. • Eichhornia azurea: Bot. Mag. 106 (1880). • Eichhornia crassipes, as Pontederia: Martius, Nova Gen. et Spec. Pl. Brasiliensium (1824). • Pontederia cordata: Bot. Mag. 29–30 (1809). • Pontederia azurea: Bot. Mag. 56 (1829). • Heteranthera zosteraefolia: Martius, Nova Gen. et Spec. Pl. Brasiliensium (1824). • Le Maout and Decaisne: Pontederia.

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.’.