Rice field weed flora of Sri Lanka.
The weed flora associated with rice fields in Sri Lanka is presented. Weed spp. belonged to 32 families, the most important being the Cyperaceae and Gramineae which represented 54% of the total weed spp. Cyperus haspan, Fimbristylis miliacea and Isachne globosa were the most abundant (<70%) weed spp. with the most extensive distribution in both the wet and dry zone of rice production. Amongst the 134 spp. identified, 4 were pteridophytes (Azolla pinnata, Salvinia auriculata, Marsilea quadrifolia and Ceratopteris thalictroides), 2 were algae (Spirogyra and Chara spp.), and 88 monocotyledonous and 40 dicotyledonous spp. from 3, 2, 11 and 16 families, resp. The most widespread and abundant weed spp. apart from Cyperus iria and Echinochloa spp. belonged to the group of hydrophytic weeds which are rooted in water-saturated soil in at least the early part of their lives. Mesophytic weed spp. including Ageratum conyzoides, Setaria glauca [S. pumila], Cynodon dactylon, Cyperus rotundus, Eleusine indica and several other spp. were considered important weeds of upland but not of lowland rice cultures.