Abstract
That stalks reorient after flowering to face upwards is a common phenomenon in many flowering plants, indicating the potential importance of fruit orientation on seed dispersal. But this idea has not been subject to an empirical test. We examined this hypothesis by analysing the evolutionary correlation between fruit orientation and other characters and by investigating the effects of fruit orientation on seed dispersal. We found that 1) in a sub-alpine plant community, upward fruit orientation strongly correlates with fruits that act as seed containers, which are often of dry type and are dispersed by non-animal vectors; 2) as exemplified by the Campanulaceae s. str., fruit orientation strongly correlates with dehiscence position. Upwardly-oriented capsules dehisce at the apex, whereas pendent ones dehisce at the base, in both cases ensuring that seeds are released from an upright position; 3) in manipulation experiments on Silene chungtienensis, upward fruits (the natural state) exhibit much greater dispersal distances and more dispersive pattern than pendent ones, and have a more even distribution of dispersal direction than horizontal ones. Our results suggest that fruit orientation may have important function in seed dispersal, which may be the reason why the phenomenon that stalk erection after flowering occurs widely.
Highlights
The fruit is a characteristic structure in flowering plants, and its character affect the way of seed dispersal
The distribution of the fruit characters is shown in Supplementary Fig. S1
Both the upward-oriented fruit (53 cases) and the stalk erection phenomenon (33 cases, characterized by a non-upward-oriented flower followed by an upward fruit) occur more frequently in fruits that act as seed containers, in taxa with dry fruits and are dispersed by non-animal vectors (Table 1 and Supplementary Table S1)
Summary
The fruit is a characteristic structure in flowering plants, and its character affect the way of seed dispersal. There are numerous fruits that do not separate from their mother plants, acting solely as seed containers (e.g., most capsules and follicles) For these plants, the effects of fruit characters on seed dispersal have received much less attention. In a study on Anisodus luridus (Solanaceae), Wang et al.[10] suggested that the erect stalks hold rainwater within the persistent calyx, providing better conditions for seed development This mechanism may not be widely applicable to other plants that show similar phenomenon. Whether or not the hypothesis is a reasonable one, we lack knowledge about the way in which fruit orientation may affect seed dispersal To test this hypothesis, the first question we asked was: do some taxa exhibit upward fruit or stalk erection more frequently than others? We would expect a correlation between fruit orientation and dehiscence position in these plants
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