Family Aponogetonaceae

Aponogetonaceae J.G. Agardh

Habit and leaf form. Herbs; laticiferous. Perennial; cormous, or rhizomatous. Hydrophytic; rooted. Leaves emergent and floating. Often heterophyllous. Leaves alternate; petiolate; sheathing. Leaf sheaths with free margins. Leaves simple. Lamina parallel-veined; cross-venulate (the tissue between the veins breaks up as the leaf matures, leaving a network with holes). Axillary scales present.

General anatomy. Plants with laticifers (articulated). Accumulated starch exclusively ‘pteridophyte type’.

Leaf anatomy. Stomata present (on floating leaves); paracytic.

Lamina without secretory cavities (assuming that Cronquist’s ‘with well developed secretory canals’ refer to laticifers). The mesophyll containing calcium oxalate crystals. The mesophyll crystals solitary-prismatic (? — no mention of raphides). Minor leaf veins without phloem transfer cells (Aponogeton). Vessels absent.

Stem anatomy. Secondary thickening absent. Xylem without vessels.

Root anatomy. Root xylem with vessels, or without vessels; vessel end-walls scalariform.

Reproductive type, pollination. Unisexual flowers absent. Plants hermaphrodite. Floral nectaries present. Nectar secretion from the gynoecium (from the sides of the carpels). Pollination entomophilous; via beetles, or via hymenoptera.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’ (commonly projected above the water in 1–3 spikes). Inflorescences pseudanthial (sometimes), or not pseudanthial; spatheate (the spathe caducous). Flowers small; usually very irregular; when irregular (i.e. usually), zygomorphic. The floral irregularity involving the perianth. Flowers cyclic, or partially acyclic. Sometimes the gynoecium acyclic. Perigone tube absent.

Perianth of ‘tepals’, or absent; when present, (1–)2(–6); free; 1 whorled; petaloid; when present, white (usually), or blue, or purple.

Androecium 6 (usually 3 + 3), or 25–100 (i.e. sometimes ‘many’). Androecial members branched (when ‘many’), or unbranched; 2–4 whorled. Stamens 6(–50); diplostemonous to polystemonous. Anthers dehiscing via longitudinal slits; extrorse, or latrorse; tetrasporangiate. Endothecium developing fibrous thickenings. The endothecial thickenings spiral. Microsporogenesis successive, or simultaneous. The initial microspore tetrads tetrahedral, or decussate. Anther wall of the ‘monocot’ type. Pollen grains aperturate; 1 aperturate; sulcate; 3-celled.

Gynoecium (2–)3–6(–9) carpelled. Carpels isomerous with the perianth, or reduced in number relative to the perianth, or increased in number relative to the perianth. Gynoecium apocarpous; eu-apocarpous to semicarpous (basally fused to varying extents); superior. Carpel apically stigmatic; 1–8 ovuled. Placentation basal. The ‘odd’ carpel anterior. Stigmas dry type; papillate; Group II type. Ovules ascending; anatropous; crassinucellate. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; persistent. Synergids pear-shaped. Endosperm formation helobial.

Fruit non-fleshy; more or less an aggregate. The fruiting carpel dehiscent; a follicle. Seeds non-endospermic. Seeds with starch. Cotyledons 1 (bifacial). Embryo chlorophyllous; straight. Testa without phytomelan (?); fleshy or membranous.

Seedling. Germination phanerocotylar. Hypocotyl internode present (short). Seedling collar not conspicuous. Cotyledon hyperphyll elongated; assimilatory; dorsiventrally flattened. Coleoptile absent. Seedling non-macropodous. Seedling cataphylls absent. First leaf dorsiventral. Primary root ephemeral.

Physiology, biochemistry. Not cyanogenic. Alkaloids absent (2 species). Proanthocyanidins present, or absent; when present, cyanidin. Flavonols present; kaempferol and quercetin, or quercetin. Ellagic acid absent. Saponins/sapogenins absent.

Geography, cytology. Sub-tropical and tropical. Palaeotropical and South Africa. X = 8.

Taxonomy. Subclass Monocotyledonae. Superorder Alismatiflorae; Hydrocharitales. APG (1998) Monocot; non-commelinoid. APG 3 (2009) Order: Alismatales.

Species 47. Genera 1; only genus, Aponogeton.

Economic uses, etc. Some aquarium and watergarden ornamentals.

Illustrations.
• Technical details: Aponogeton, Ouvirandra (= Aponogeton).

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