5. Myriophyllum dicoccum F. Mueller, Trans. Philos. Inst. Victoria. 3: 41. 1859.
二分果狐尾藻 er fen guo hu wei zao
Plants monoecious and with bisexual flowers. Stem sparsely branched, 30-50(-80) cm; internodes 2-12 mm. Submerged leaves scattered or 2-5-whorled, pectinate, broadly ovate in outline, 2-3 × 1-2 cm; segments in 4-12 pairs, filiform, 5-10 mm, apex finely mucronate; emergent leaves alternate, linear to narrowly oblanceolate, 0.7-1.7 × 0.5-1.5 cm, margin entire or shortly toothed distally. Inflorescence of axillary, irregular dichasia of 1-5 flowers, female ones remaining submerged throughout development, male and bisexual ones borne on emergent part of stem; bracts leaflike; bracteoles deltoid, inconspicuous. Male flowers sessile, 4-merous; sepals deltoid, ca. 0.2 mm; petals red, ca. 1.8 mm, late caducous; stamens 4. Female flowers sessile or pedicellate, 2-merous; sepals deltoid, ca. 0.1 mm; petals absent or vestigial; ovary 2-loculed; styles clavate; stigmas red, capitate, not fimbriate. Bisexual flowers sessile, 4-merous; stigmas developing after pollen release, fimbriate. Fruit sessile or shortly pedicellate, olive-brown, 2-loculed (female flowers) or 4-loculed (bisexual flowers), ca. 1 mm; mericarps cylindric, smooth or sparsely tuberculate, apex truncate. Fl. and fr. May-Sep.
Fujian, Guangdong, Taiwan [E India, Indonesia (NE Java), Papua New Guinea, Vietnam; Australia].
Myriophyllum dicoccum was erroneously treated as M. humile (Rafinesque) Morong (Burshia humilis Rafinesque) in FRPS (53(2): 140. 2000). These taxa are separated by their fruit: M. dicoccum has 2-loculed fruit from female flowers and 4-loculed fruit from bisexual flowers on the same plant, whereas M. humile has only 4-loculed fruit.