FRUIT POLYMORPHISM IN EPHEMERAL SPECIES OF NAMAQUALAND .3. GERMINATION DIFFERENCES BETWEEN THE POLYMORPHIC DIASPORES

Fruit polymorphism, an adaptation to arid environments, was examined in four species of the Asteraceae, namely Dimorphotheca sinuata, Dimorphotheca polyptera, Arctotis fastuosa and Ursinia cakilefolia. The optimum germination requirements for both the disc and ray diaspores of D. sinuata were from 7°C to 22°C in the light although the disc diaspores germinated better (≥ 95·5%) than the my diaspores (≤ 3%). Highest germination of disc diaspores of D. polyptera was evident from 7°C to 17°C in the dark. Germination of winged ray diaspores germinated optimally from 7°C to 12°C in the dark while the unwinged ray diaspores germinated at an optimum temperature of 12°C in light as well as dark. Optimum germination percentages of both the diaspores of A. fastuosa were obtained at 32°C in the light. The white diaspores of U. cakilefolia germinated best in the light at 20°C while black diaspores germinated optimally at alternating temperatures of 20°C/10°C and 25°C/15°C. The disc diaspores of D. sinuata showed changes in their germinability over one year. Dormancy of poorly germinating diaspores was found to be enforced by both mechanical and chemical resistance of the pericarp. © 1993 Academic Press Limited.