Abstract: Cenchrus pauciflorus Benth. is one of the most invasive weeds in Horqin Sandy Land. To explore the seed heteromorphism and population maintenance strategy of C. pauciflorus, we assessed the biological characteristics and germination traits of seeds, and the effects of artificial removal on the germination of P-type seeds. The results showed that two or more seeds were detected in the same bur of the C. pauciflorus (most contained two seeds). One type of seeds was bigger and looks like mango (type M), and the other type was smaller and looks like plum (type P). Seed length, width, height and weight were significantly higher for M-type seeds than P-type seeds. However, the variations of seed characteristics for P-type seeds were higher than M-type seeds. In natural habitats, the probability of one seed (M-type) germinated in one bur reached 93%, while the rate of two seeds (both M-type and P-type) germinated in the same bur was only 7%. We did not detect three seeds germinated in the same bur in the natural habitats. In laboratory germination experiment, the germination rate of one seed germinated in one bur was 69.3%, that of two seeds germinated in the same bur was 22.2%, and that of three seeds germinated  in the same bur was 8.5%. Results from the field artificial removal experiment showed that clipping C. pauciflorus seedlings in spring had weak effect on its population size, while clipping C. pauciflorus adult plants in summer significantly reduced the population size of C. pauciflorus. The germination rate of P-type seeds was only 20.15% after removal of the radicle and germ of the germinated M-type seeds. Our results indicated that P-type seeds may play a unique role in maintaining C. pauciflorus population, which is subject to environmental factors and with a threshold.

Key words: Cenchrus pauciflorus Benth., seed heteromorphism, germination mechanism, life history strategy.