Growth of hybrids between the common and early ecotypes of Imperata cylindrica

Growth of hybrids between the common‐ (C‐) and early‐ (E‐) ecotypes of cogongrass ( Imperata cylindrica (L.) Raeusch.) was compared with their parents to clarify their potential invasiveness. Six ramets of each artificial hybrid and their parents, a total of 276 ramets (6 ramets × 22 hybrids between C‐ and E‐type ( CE ‐hybrids), 6 ramets × 22 hybrids between E‐ and C‐type ( EC ‐hybrids), six ramets of C‐type parent and six ramets of E‐type parent) were transplanted individually into clay pots (21‐cm diameter × 16‐cm depth, 3300 cm 3 ) in May. Half of the clay pots planted with CE ‐hybrids, EC ‐hybrids, C‐type parents and E‐type parents, three ramets of each clone, were placed in wet conditions (wet plot), in which all of the clay pots were kept in water 9.5 cm deep from the bottom of the pot. As controls, the remaining clay pots were placed on the ground. All ramets were harvested in November and their dry weights were measured. The E‐type grew better than C‐type in the wet plot. CE ‐hybrids and EC ‐hybrids showed a broad range of growth response to groundwater level and some hybrids were superior to their parents under both control and wet conditions. In the Tohoku region, the hybrids are commonly distributed, hybridization can cause the two parent types to fuse into a single population and would result in their extinction.