Annals of Botany

All together now – doing it in synchrony

I am writing this on a train journey between Southampton and Exeter and we have passed many fields of maize (corn) waiting to be harvested. That harvest, of course, has depended on wind pollination earlier in the year. This is generally not a limiting factor; in large stands of a single variety, pollen has no trouble in ‘finding’ a receptive stigma. However, in natural ecosystems it is a different story. Plant numbers and plant density are much lower and consequently the likelihood of successful pollen transfer is reduced. Some remarkable strategies have evolved to maximize reproductive success, one spectacular example of which is discussed by Michalski and Durka (Halle, Germany, pp. 1271-1285). They have studied flowering patterns in populations of several Juncus species growing in the Halle area. In different species of Juncus the flowering period ranges from 7 to 42 d, but individual flowers are short lived with anthesis taking place over 1 d or less. In this very careful investigation, between nine and 24 individual flower spikes (one selected per plant) were tagged in each population. For all species except J. atratus (which was pot grown), populations were of wild plants, comprising several hundred to several thousand individuals and covering between 200 and 630 000 m². Flowering times were observed for all the tagged spikes. In all species, there was a clear tendency for all flowers on one spike to open together; in some species this synchrony was very marked. Even more remarkable, synchrony was also seen at population level so that pulses of flower opening were interspersed with days when no flowers opened. The actual pattern varied between species. Juncus effusus, for example, exhibited one major flowering episode while other species exhibited several. Although Juncus species are self-fertile, this synchronous flowering strategy clearly increases out-breeding by ensuring that wind-blown pollen has a greater chance of reaching another open flower.