Including Damasoniaceae Nakai, Borboraceae Dulac (p.p.), Elismataceae Nak.
Habit and leaf form. Herbs; laticiferous. Annual (rarely), or perennial; with a basal aggregation of leaves; rhizomatous. Hydrophytic, or helophytic; rooted. Leaves submerged and emergent. Heterophyllous (often), or not heterophyllous. Leaves alternate; petiolate, or sessile; sheathing; simple. Lamina pinnately veined (or parallel-pinnate), or palmately veined, or parallel-veined; cross-venulate, or without cross-venules. Axillary scales present.
General anatomy. Plants without laticifers (the latex occuring in canals). Accumulated starch exclusively ‘pteridophyte type’.
Leaf anatomy. Stomata present; paracytic, or tetracytic (rarely).
Lamina with secretory cavities. Secretory cavities containing latex; schizogenous. The mesophyll containing calcium oxalate crystals, or without calcium oxalate crystals. The mesophyll crystals druses (?), or solitary-prismatic (? — no raphides). Minor leaf veins without phloem transfer cells (4 genera). Vessels absent.
Stem anatomy. Secretory cavities present; with latex. Secondary thickening absent. Xylem without vessels. Sieve-tube plastids P-type; type II.
Root anatomy. Root xylem with vessels; vessel end-walls scalariform, or scalariform and simple (mostly mainly simple).
Reproductive type, pollination. Plants hermaphrodite, or monoecious, or dioecious (rarely), or polygamomonoecious. Floral nectaries present. Nectar secretion from the perianth, or from the gynoecium, or from the androecium (from the tepal or stamen bases in Echinodorus, but usually from the bases of the sides of the carpels).
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’ (usually), or solitary. The ultimate inflorescence unit cymose, or racemose. Inflorescences scapiflorous; paniculate, often complex with verticils of branches, sometimes umbellate through reduction of the whorls to one; with involucral bracts, or without involucral bracts. Flowers bracteate; regular; 3 merous; cyclic; tetracyclic to polycyclic. Perigone tube absent.
Perianth with distinct calyx and corolla; 6; free; 2 whorled; isomerous; different in the two whorls; white, or red, or pink (inner), or green (outer). Calyx 3; 1 whorled; polysepalous. Corolla 3; polypetalous; white, or red, or pink.
Androecium (3–)6 (in one cycle), or 18–100 (i.e. to many). Androecial members branched (usually, e.g. Alisma having three stamen pairs, while forms with numerous stamens have them seemingly spiralled, but actually reflecting whorls of trunk bundles), or unbranched (occasionally); when in more than one whorl, maturing centripetally; free of the perianth; free of one another (usually, ostensibly), or coherent (in pairs, or in anatomically determinable bundles); 1–20 whorled (i.e., to ‘many’ whorls). The androecial bundles (or the pairs, in Alisma) alternating with the corolla members. Androecium exclusively of fertile stamens. Stamens 3, or 6, or 18–100 (i.e. to ‘many’); reduced in number relative to the adjacent perianth, or isomerous with the perianth to polystemonous; alterniperianthial. Anthers dehiscing via longitudinal slits; extrorse. Endothecium developing fibrous thickenings. The endothecial thickenings girdling. Microsporogenesis successive. The initial microspore tetrads isobilateral. Anther wall of the ‘monocot’ type. Pollen grains aperturate; 2–3 aperturate, or 9–29 aperturate; foraminate; 3-celled.
Gynoecium 3 carpelled, or 6–100 carpelled (or more — i.e. to many); apocarpous; eu-apocarpous; superior. Carpel apically stigmatic, or with a lateral style, or with a gynobasic style; 1 ovuled, or 2 ovuled (rarely more). Placentation basal. Stigmas dry type; papillate; Group II type. Ovules ascending; anatropous, or amphitropous; weakly crassinucellate. Embryo-sac development Allium-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed, or not formed; when formed, 1; not proliferating. Synergids hooked (usually with filiform apparatus). Endosperm formation helobial, or nuclear (?).
Fruit non-fleshy; an aggregate. The fruiting carpels not coalescing. The fruiting carpel dehiscent, or indehiscent; a follicle, or an achene. Seeds non-endospermic. Seeds with starch. Cotyledons 1. Embryo achlorophyllous (3/5); strongly curved (horseshoe-shaped). Testa without phytomelan; usually membranous, sometimes thinly leathery, then brown.
Seedling. Germination phanerocotylar. Hypocotyl internode present (quite long, in Baldellia). 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.
Physiology, biochemistry. Cyanogenic (?), or not cyanogenic. Alkaloids present, or absent (2 species investigated). Iridoids not detected. Proanthocyanidins present, or absent; when present, cyanidin. Flavonols present, or absent; when present, kaempferol and quercetin. Ellagic acid absent. C3 and CAM. C3 physiology recorded directly in Alisma, Sagittaria. CAM recorded directly in Sagittaria subulata (aquatic CAM only). Anatomy non-C4 type (Sagittaria).
Geography, cytology. Temperate, sub-tropical, and tropical. Cosmopolitan. X = (5-)7–11(-13).
Taxonomy. Subclass Monocotyledonae. Superorder Alismatiflorae; Alismatales. APG (1998) Monocot; non-commelinoid. APG 3 (2009) Order: Alismatales.
Species 90. Genera 11; Alisma, Baldellia, Burnatia, Caldesia, Damasonium, Echinodorus, Limnophyton, Luronium, Ranalisma, Sagittaria, Wiesneria.
Economic uses, etc. Includes important aquarium and pond ornamentals, and some Sagittaria species have edible rhizomes.
• Technical details: Alisma plantago-aquatica, Luronium natans.
• Technical details: Sagittaria, Damasonium.
• Alisma plantago-aquatica (B. Ent.).
• Alisma plantago-aquatica: as A. plantago, Eng. Bot. 1437 (1869).
• Baldellia ranunculoides: as Alisma, Eng. Bot. 1439 (1869).
• Baldellia ranunculoides var. repens: as Alisma, Eng. Bot. 1440 (1869).
• Damasonium alisma (B. Ent.).
• Limnophyton (Thonner).
• Luronium natans: as Alisma, Eng. Bot. 1441 (1869).
• Sagittaria sagittifolia (B. Ent.).
• Sagittaria sagittifolia: Eng. Bot. 1436 (1869).