Commelina benghalensis, a kind of invasive weed, can develop new populations through seed reproduction as well as vegetative reproduction. Besides the overground reproductive shoots, it can also generate underground reproductive shoots especially when suffered injury. Like the overground shoots, the underground shoots can develop self-pollinated flowers and improve the amount of underground seeds. Therefore, the whole plant of C. benghalensis can produce four types of seeds, namely, overground large(OL) seeds, overground small(OS) seeds, underground large(UL) seeds and underground small(US) seeds. But the reproductive effort of C. benghalensis to the four types of seeds and their reproductive strategies and reproductive cost are still unknown. In this study, the morphologic characters, germination and growth of seedlings of the four types of seeds were observed, and the reproductive effort to the four types of seed and the reproductive cost were analyzed.
The results showed that both the overground and underground shoots of C. benghalensis could develop capsules. In every capsule, there were one large seed and 2～4 small seeds. Studies on these four types of seeds showed significant differences in the seed weight, which were 1.0547 g, 0.4400 g, 0.5980 g and 0.3145 g per 100 seeds, respectively. The germination of small (OS and US) seeds was not synchronous and was long-drawn, and the germination rate of US seeds was 80%, obviously higher than of OS seeds, so did the seed vigor. While the germination rate of large (OL and UL) seeds was similarly 97%, the UL seeds had a higher vigor than the OL seeds. The area, perimeter, length and width of first leave blades, which were developed from four types of seeds, were remarkably different, in the order of UL>OL>US>OS.
The reproductive effort of C. benghalensis was mainly the overground seeds, especially the overground small seeds, only very few resources were allocated to the underground seeds. And the reproductive cost of underground seeds was higher than overground seeds, but when it was injured, the underground seeds especially the underground large seeds could help the species survive and propagate normally.