Family Pontederiaceae

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). Annual, or perennial; with a basal aggregation of leaves, or with neither basal nor terminal 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 at the base. Leaves ligulate, or eligulate; stipulate (if the axillary hyaline structures are so interpreted), or exstipulate. Lamina margins entire.

General anatomy. Accumulated starch other than exclusively ‘pteridophyte type’.

Leaf anatomy. Stomata present; paracytic. Hairs absent.

The mesophyll containing calcium oxalate crystals. The mesophyll crystals raphides, or solitary-prismatic. Minor leaf veins without phloem transfer cells (Eichornia, Pontederia). Vessels absent.

Stem anatomy. Secondary thickening absent. Xylem with vessels (sometimes), or without vessels. Vessel end-walls scalariform.

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

Reproductive type, pollination. Unisexual flowers absent. 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’; in racemes, or in spikes, or in panicles. The ultimate inflorescence unit 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; without spots, or spotted (occasionally); 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 (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, biochemistry. Not cyanogenic. Alkaloids present, or absent. Proanthocyanidins present; cyanidin, or cyanidin and delphinidin. Flavonols absent. Ellagic acid absent. Saponins/sapogenins absent. C3. C3 physiology recorded directly in Eichornia. Anatomy non-C4 type (Pontederia).

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 3 core angiosperms; Superorder Lilianae; commelinid Monocot; Order Commelinales.

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

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

Illustrations.
• Technical details: Pontederia.