Willows (Salix genus) are one of the earliest flowering tree species in the UK and are a fantastic nectar source for early pollinators such as bumblebees and butterflies. These trees are dioecious which means that there are separate male and female trees which can be distinguished by their flowers. Another more commonly known example of a dioecious tree would be the holly – only the female trees bear the red berries. One of the traditional names for willow flowers was ‘vegetable goslings’ which seems a perfect description to me!
The flowers are quite unusual when compared with a simple flower such as a buttercup which follows the classic textbook diagram. Willow flowers are catkins – these are spikes of numerous tiny flowers rather than each catkin representing a single flower. Each of the yellow-tipped spikes in the male flower is one of the stamens and there are generally two or more of these to each individual flower within the catkin – the number varies with species. The same is true, although less easily illustrated, for the female flowers which have two or more stigmas per flower.
The male and female flowers appear at the same time in order that the pollen from the male flowers is able to fertilise the female flowers. The flowers are quite different from one another in appearance and, side by side, it would be easy to assume that a male and a female willow tree were two different species.
The willow flowers are an excellent source of nectar for early pollinating species, such as queen bumblebees which have emerged from hibernation and are establishing nests, or the early Nymphalidae butterflies which hibernate through the winter.