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Water-milfoil Family

Robin W. Scribailo
Mitchell S. Alix

Herbs, perennial [annual], or shrubs, usually monoecious, rarely dioecious, usually aquatic to semiaquatic, sometimes terrestrial, unarmed, ± clonal. Roots: taproots or fibrous, and then often with adventitious nodal roots; rhizomes sometimes present [stolons in some Haloragis]. Stems erect, ascending, decumbent, or prostrate, cylindric to 4-ribbed, glabrous or scabrous to pubescent, hairs uniseriate and multiseriate, glands present or absent. Turions present or absent, lateral and/or terminal. Leaves opposite, alternate, or subverticillate to whorled, simple, often heteromorphic in Myriophyllum and Proserpinaca; stipules absent; sessile or petiolate; blade lobed, unlobed, or pinnatifid to pectinate, margins entire or serrate, surfaces glabrous or scabrous. Inflorescences terminal or lateral in axils of bracts or leaves, determinate or indeterminate, dichasia (Haloragis and Proserpinaca), or simple racemes (Myriophyllum); bracts and bracteoles present. Flowers bisexual or unisexual, staminate and pistillate usually on same plant, sessile or pedicellate (sometimes sessile in pistillate flowers of Myriophyllum); perianth and androecium epigynous; hypanthium subglobose; sepals persistent, (3 or)4, sometimes rudimentary (Myriophyllum), petals often caducous, sometimes persistent, (3 or)4, or 0 or rudimentary (Proserpinaca), keeled, cucullate, often distally cupulate; stamens 3–8 (1 or 2 times as many as sepals); anthers basifixed, dehiscing longitudinally; pistil 1, 3- or 4-carpellate; ovary 1, inferior, 1–4-locular; placentation axile; styles 1 per locule; stigmas 1 per locule, clavate, capitate, fimbriate; ovules 1(or 2, in Haloragis and Proserpinaca), anatropous, bitegmic, crassinucellate. Fruit a nutlet, indehiscent, or schizocarp, splitting into (2–)4 mericarps; exocarp glabrous, scabrous, rugose, tuberculate, or papillate, sometimes with ribs, ridges, or wings. Seeds 1 per locule; embryo straight, cylindric; endosperm ± copious and fleshy.

Genera 10, species ca. 120 (3 genera, 17 species in the flora): North America, Mexico, West Indies, Bermuda, Central America, South America, Eurasia, Africa, Indian Ocean Islands, Pacific Islands, Australia.

Morphologically, Haloragaceae are defined by the following floral characters: an epigynous ovary, usually 3- or 4-merous floral organization (always 3-merous in Proserpinaca), sometimes 2-merous, cucullate petals, and fruit a nutlet or schizocarp with 1 or 2 ovules per locule. In the aquatic members of the family, reliance on vegetative characters that are highly plastic and have evolved independently by convergent evolution has proven to be of limited usefulness for the delimitation of taxa (M. L. Moody and D. H. Les 2007).

J. Hutchinson (1959) suggested that Haloragaceae is closely allied to Onagraceae based on embryology, pollen morphology, and floral vasculature. A. Cronquist (1968) and A. L. Takhtajan (1969) believed Haloragaceae to be more closely allied to Podostemaceae. The work of A. E. Orchard (1975, 1985) has been important in circumscribing the family.

Molecular phylogenetic studies have placed Haloragaceae within the core eudicot order Saxifragales (D. R. Morgan and D. E. Soltis 1993; Soltis et al. 1997b). Gunnera, which had long been included within the family, has been moved to the monogeneric family Gunneraceae in Gunnerales (Angiosperm Phylogeny Group 2009).

SELECTED REFERENCE Moody, M. L. and D. H. Les. 2007. Phylogenetic systematics and character evolution in the angiosperm family Haloragaceae. Amer. J. Bot. 94: 2005–2025.

1 Flowers unisexual or bisexual, proximal pistillate, distal staminate, often with intermediate transitional zone of bisexual flowers; fruit a schizocarp, splitting into (2–)4 mericarps; plants aquatic or semiaquatic   2 Myriophyllum, p. 14
+ Flowers bisexual; fruit a nutlet, indehiscent; plants aquatic, semiaquatic, or terrestrial.   (2)
2 (1) Flowers 4-merous; plants shrubs or herbs, terrestrial   1 Haloragis, p. 13
+ Flowers 3-merous; plants herbs, aquatic or semiaquatic   3 Proserpinaca, p. 29

Lower Taxa


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