HALORAGACEAE (water-milfoil family)
Contributed by Alan E. Brant and George Yatskievych
Plants perennial
herbs (woody elsewhere), sometimes monoecious or dioecious, often with rhizomes
(these seldom collected in submerged aquatics), glabrous (in some species,
young growth sometimes sparsely short-hairy). Stems unbranched or branched,
sometimes rooting at the nodes. Leaves alternate, opposite, and/or whorled,
sessile or short-petiolate. Stipules absent. Leaf blades simple and toothed to
pinnately dissected (often both extremes present on the same plant). Flowers in
terminal spikes or axillary and solitary or in small clusters, sessile or
nearly so, perfect or imperfect (the lowermost flowers then usually pistillate,
the others staminate), the pistillate and perfect ones epigynous,
actinomorphic, each subtended by a pair of minute bracts. Calyces of 3 or 4
sepals, these free, sometimes shed as the flower opens, small, triangular.
Corollas absent or of 4 petals, these free, shed early, membranous, small.
Stamens 3–8, free, the filament short, the anthers attached at the base.
Pistils 1 per flower, of 3 or 4 fused carpels. Ovary inferior, with 3 or 4
locules, each with 1 ovule, the placentation apical. Styles absent or short,
the stigmas 4, appearing feathery and curved outward. Fruits nutlike,
indehiscent or eventually splitting from the tip into 4 nutlets. Seeds 3 or 4,
not easily separable from the fruit wall. Nine genera, 145 species, nearly
worldwide, most diverse in the southern hemisphere.
Species of
Haloragaceae are submerged or emergent aquatics, sometimes on muddy margins of
wetlands. The submerged taxa provide valuable habitat for small fish and
aquatic invertebrates and also generate oxygen for the waters in which they
grow. However, the more aggressive species can choke out other aquatic plants
and can contribute to eutrophication of ponds and lakes.