Aspens flowering
Vello Keppart photographed aspens in Jõgeva at LK’s request
Translation Liis
The catkins of a flowering male aspen spread pollen in the wind
Cross section of a female catkin showing the green ovaries and the red stigmas
Aspen Harilik haab or haab Populus tremula
The flowering of aspens usually tends to be overlooked but they are trees with a rather interesting way of life.
Depending on the spring weather aspens flower around mid-April and the pollination lasts around a week but the modest cylinder-shaped grey catkins in the tree tops often stay unnoticed.
The red male catkins are not releasing pollen yet, the grey catkin has already finished its flowering
The female flowers of an aspen are hidden
Aspens mostly spread vegetatively although they also grow well from seed. It is a dioecious tree, meaning that one tree only carries flowers of one sex – either male or female. If an aspen grows on its own or in a smaller aspen stand then all aspens in the stand will probably have the same sex simply because they all have started to grow from root suckers of one tree.
The flowers of the wind pollinated aspen are arranged in a hanging inflorescence or catkin with many flowers, and it is difficult to distinguish between the sexes.
One sign is that during flowering the male catkins that spill out pollen move more strongly in the wind due to their more flexible lengthwise axis, and the stiffer female catkins move less - but this usually only professionals note.
Investigators have found that there are up to a couple of times more male than female trees.
The longer male catkin has finished releasing pollen
Female aspen catkin
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