Aquatic or marsh herbs. Leaves linear or lanceolate. Flowers in umbel-like cymes, regular, hermaphrodite. Perianth of 6 segments, all, or the inner ones only, petal-like. Stamens 9, very rarely fewer. Pollen-grains globular. Carpels 6, very rarely fewer, distinct or united at the base only, opening when ripe along the ventral suture. Ovules on irregularly branched parietal placentas, numerous, inverted. Seeds without albumen.--Genera 2, species 2. North and Central Africa. (Under _ALISMACEAE_.) Perianth-segments nearly equal, all petal-like, pink, persistent. Embryo straight. Leaves linear. Juice not milky.--Species 1. North-west Africa (Algeria). Used as a garden plant. The root-stock is edible. “Flowering-rush.” =Butomus= Tourn. Perianth-segments unequal, outer sepal-like, inner petal-like, white, falling off very early. Embryo horseshoe-shaped. Leaves elliptical. Juice milky.--Species 1. Northern part of Central Africa. (_Butomopsis_ Kunth) =Tenagocharis= Hochst. FAMILY 14. HYDROCHARITACEAE Aquatic herbs. Leaves with axillary scales. Flowers enclosed when young in a one-or several-flowered spathe of one or two bracts, regular, rarely somewhat irregular. Perianth consisting of a calyx and a corolla, rarely simple. Stamens 2-12. Anthers opening outwards or laterally. Ovary inferior, more or less distinctly one-celled, with 2-15 parietal placentas, which sometimes form incomplete dissepiments. Seeds without albumen.--Genera 10, species 40. (Plate 7.) 1. Stigmas 2-5. Placentas as many, slightly raised. 2 Stigmas 6 or more. Placentas as many, much projecting and generally meeting in the centre of the ovary. 6 2. Petals none. Stamens 3. Pollen-grains filiform. Stigmas several times as long as the sepals. Embryo with a strongly developed radicle. Totally submerged marine plants. Leaves more or less distinctly stalked.--Species 2. Indian Ocean. [Subfamily =HALOPHILOIDEAE=.] =Halophila= Thouars Petals present, but sometimes very small and falling off very early. Pollen-grains globular. Stigmas at most twice as long as the sepals. Embryo with a not very strongly developed radicle. Freshwater plants; flowers raised above the water. Leaves sessile. [Subfamily =VALLISNERIOIDEAE=.] 3 3. Leaves whorled. Spathes 1-flowered. Flowers unisexual. Stamens 3.--Species 1. Upper Nile, Madagascar, Mauritius. Used in refining sugar. [Tribe HYDRILLEAE.] =Hydrilla= L. C. Rich. Leaves spirally arranged. Spathes of the male flowers several-flowered. 4 4. Spathes of the male flowers 2-10-flowered, not breaking away from the stem. Stamens 3-9. Ovules inverted.--Species 3. Madagascar and Angola. [Tribe BLYXEAE.] =Blyxa= Noronha Spathes of the male flowers many-flowered, breaking away from the stem. Stamens 2-3. Ovules straight. [Tribe VALLISNERIEAE.] 5 5. Male flowers regular, with 3 fertile and 2-4 sterile stamens. Stigmas linear, 2-cleft or 2-parted. Leaves one-nerved. Stem elongated.--Species 10. Tropical and South Africa. =Lagarosiphon= Harv.