|Catkins of quaking aspen, Populus tremuloides, began emerging in March in southern Minnesota. This photo was taken in mid-April.|
Catkins, also called aments, are cylindrical, sometimes pendant clusters of inconspicuous flowers. They are typical of willows, aspens, poplars, birches, alders, hazelnuts and ironwood trees and shrubs. All these plants bloom in spring, often before leaves emerge, and most are wind pollinated. Willows are also insect pollinated and can be an important source of pollen and nectar for early-emerging insects, including those that later pollinate crops (1).
Catkins contain either male (pollen producing) or female (seed producing) flowers on the same or different plants. Ironwood (Ostrya virginiana), hazelnuts (Corylus spp.), birches (Betula spp.) and alders (Alnus spp.) have male and female catkins on the same plants, so they’re said to be monoecious (mon-EE-shus), which means “one house.”
In contrast, aspens and poplars (Populus spp.) have male and female catkins on different plants, so they’re dioecious (di-EE-shus), meaning “two houses.” Willows (Salix spp.) are also dioecious.
The emergence of catkins and the release of pollen marks not only the beginning of spring but also the start of allergy season. Wind-pollinated plants tend to produce abundant pollen because the grains could land anywhere – perhaps on a female flower of the same species, but maybe on those of a different species or even on no plant at all. Such as on you.Flurries of pollen may add to the misery for allergy sufferers, but for aspens, willows, and similar plants, they’re an insurance policy. The possibility of a next generation literally blows in the wind, so the more pollen, the better. "Gesundheit" for one, then, is good fortune for the other.
1) Ostaff, D. P., Mosseler, A., Johns, R. C., Javorek, S., Klymko, J. and Ascher, J. S. 2015. Willows (Salix spp.) as pollen and nectar sources for sustaining fruit and berry pollinating insects. Can. J. Plant Sci. 95: 505516. DOI:10.4141/CJPS-2014-339.