Catkin

A catkin or ament is a slim, cylindrical flower cluster (a spike), with inconspicuous or no petals, usually wind-pollinated (anemophilous) but sometimes insect-pollinated (as in Salix). They contain many, usually unisexual flowers, arranged closely along a central stem which is often drooping. They are found in many plant families, including Betulaceae, Fagaceae, Moraceae, and Salicaceae. For some time, they were believed to be a key synapomorphy among the proposed Hamamelididae, also known as Amentiferae (i.e., literally plants bearing aments). Based on molecular phylogeny work, it is now believed that Hamamelididae is a polyphyletic group.^[1][2] This suggests that the catkin flower arrangement has arisen at least twice independently by convergent evolution, in Fagales and in Salicaceae.^[3] Such a convergent evolution raises questions about what the ancestral inflorescence characters might be and how catkins did evolve in these two lineages.

In many of these plants, only the male flowers form catkins, and the female flowers are single (hazel, oak), a cone (alder) or other types (mulberry). In other plants (such as poplar) both male and female flowers are borne in catkins.

Catkin-bearing plants include many other trees or shrubs such as birch, willow, hickory, sweet chestnut and sweetfern (Comptonia).

The word catkin is a loanword from the old Dutch katteken, meaning "kitten", on account of the resemblance to a kitten's tail.^[4] Ament is from the Latin amentum, meaning "thong" or "strap".^[5]

• Catkins in Fagales
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  Male catkins of hop-hornbeam (Ostrya carpinifolia)
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  Young male catkins of hazel (Corylus avellana)
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  Mature male catkins of hazel (Corylus avellana)
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  Alder female catkins (Alnus sp.)

• Catkins in Salicaceae
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  Young male catkin of a willow (Salix sp.)
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  Three male catkins on a willow (Salix sp.)
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  Detail of a male flowering catkin on a willow (Salix sp.)
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  Female flowering catkin on a willow (Salix sp.)

References

1. Savolainen, V., M. W. Chase, S. B. Hoot, C. M. Morton, D. E. Soltis, C. Bayer, M. F. Fay, A. Y. De Bruijn, S. Sullivan, and Y.-L. Qiu. 2000. Phylogenetics of flowering plants based on combined analysis of plastid atpB and rbcL gene sequences. Systematic Biology 49:306-362.
2. Soltis, D. E. et alii. (28 authors). 2011. "Angiosperm phylogeny: 17 genes, 640 taxa". American Journal of Botany 98(4):704-730. doi:10.3732/ajb.1000404
3. Cronk Q. C. B., Needham I., and Rudall P. J. 2015. Evolution of catkins: inflorescence morphology of selected Salicaceae in an evolutionary and developmental context. Frontiers in Plant Science. 2015; 6: 1030. doi:10.3389/fpls.2015.01030
4. "Catkin", Oxford English Dictionary (Second ed.), 1989, retrieved 30 November 2009
5. "Ament", Oxford English Dictionary (Second ed.), 1989, retrieved 30 November 2009