22. Callitrichaceae
水马齿科 shui ma chi ke
Authors: Tianlu Min & Richard V. Lansdown
Submersed, amphibious, or terrestrial herbs, rooted at nodes when terrestrial or at plant base when aquatic; stem slender. Leaves opposite, decussate, exstipulate, linear or spatulate, notched at apex, entire or very rarely toothed, somewhat congested toward apex of stems reaching water surface, to form a rosette; leaf bases often joined by a ridge of tissue extending across node, always with a midvein, often with a series of secondary veins anastomosing or looped and interconnected; scales (often described as glandular) on stems, leaves, and in leaf axils, with a short stalk and those on stem and leaves with a disk of radiating cells, those in leaf axils fan-shaped. Plants monoecious, or rarely dioecious. Flowers imperfect, minute, axillary, carpellate and staminate sometimes in same axil in various combinations; perianth absent; a subtending pair of bracts present in some species; carpellate flowers bicarpellate, often abaxial to staminate flower, stigmas 2, erect or reflexed, papillate; staminate flowers solitary, filament short or long, anther dehiscing laterally by longitudinal slits; pollen spheroidal, angular, or elongate, with 1 or more leptomata, exine intectate [or absent], sculpturing of pointed or rounded microgemmae or these absent. Fruits schizocarps, separating into 4 nutlets; nutlets dry, winged or not, wings from inner fruit layer.
One genus and ca. 75 species: widely distributed worldwide; eight species (one endemic) in China.
Ming Tien lu. 1980. Callitrichaceae. In: Cheng Mien & Ming Tien lu, eds., Fl. Reipubl. Popularis Sin. 45(1): 11-14.
