Catkin Time!

The word 'catkin' seems to derive from an old Dutch language and translates as kitten - the diminutive of cat. Catkins are common as the flower structure type for many of our trees and early country folk readily identified the furriness of these structures and compared them to furry animals. Indeed, the term 'pussy willow' for the furry catkins of sallows has the same root, while the longer, dangly catkins of trees such as Hazel and birch are also known as lamb's tails - again, a comparison with the familiar.

So why do we see a sudden mass of catkins on such a wide range of trees at this time of year? They are, for example, common amongst the oaks, beeches, hazels, birches, willows and poplars, as well as a few smaller groups of trees. What's the connection and why now? Well, trees are often large and stand head and shoulders above other vegetation. This puts them up into windier locations than those enjoyed by smaller plants - so why not use that to your advantage? Many trees are wind-pollinated rather than insect pollinated; to facilitate this, they produce huge volumes of pollen, since this is a rather random method of getting pollen from male flowers to female flowers; producing huge amounts will increase the chance that pollen will find its rightful destination. Another way to aid this distribution method is to have freely articulating anthers that waggle in the wind and thus shake out the pollen. So we see many species of trees having loosely connected rows of anthers, arranged in pendulous spikes that waggle in the wind. As an aid to encouraging cross-fertilisation with another tree, trees that produce catkins have the male and female flowers carried separately, with the females typically being much smaller and not pendulous. Most of these trees carry male and female flowers separately but on the same tree; but some species (notably the willows and poplars) have male and female flowers on separate trees.

But why are so many of them around right now? Well, if pollen is being shaken out into the wind to be carried afar, it helps to have as few obstacles in the way as possible. So deciduous trees produce their catkins in the spring, before leaves clothe the branches and get in the way.

Here's a few examples of the catkins that will be dangling away in our countryside this spring:

Hazel (Corylus avellana) catkins are perhaps the original 'lamb's tails' and smother the branches in late winter or early spring (some optimistic individuals appear before New Year's Day!)

Silver Birch (Betula pendula). Birch catkins are rather similar to those of Hazel, but appear later in the year with the first leaves - often not until late April or even early May - and are spotted with dark bracts.

Female Silver Birch catkins start life as an erect spike, with reddish stigmas poking out between the green, protective bracts. The become pendulous as the seeds develop.

Hornbeam (Carpinus betulus) is a member of the birch family and this can be seen in the structure of the male catkins, which have the pollen-bearing anthers protected from the worst of the weather by a series of bracts. 

Female Hornbeam catkins are quite different from those of birches - and very different from the male catkins. They have relatively large, leafy bracts with silky hairs that protect the white, hair-like stigmas from bad weather.

European Beech (Fagus sylvatica). Beeches have rather short, oval catkins, but they hang on long stalks that project them away from the unfurling leaves. Here you can see three male catkins on the left, with their now withered and spent anthers, then a chunkier female catkin to the right, with its 'brush' of hair-like stigmas.

The male catkins of Common Oak (Quercus robur) are typical of most oak species. They are looser and more open than the catkins of other tree families and hang in bundles rather than singly. These should be appearing in about another two weeks time, in mid-April.

Black Poplar (Populus nigra ssp. betuloides). These are the female catkins of our native Black Poplar, a rather rare species in the UK, although a recent trend to plant more has boosted the population. Poplars carry male and female flowers on separate trees and this can be useful if you find one of the many hybrid poplars that abound in our landscapes. Hybrid poplars mostly derive from deliberate cross-pollination of various forms, or selections from a range of plants to produce named clones which are all identical and propagated vegetatively. Thus, whether the tree is male or female (as determined by the flowers) is a useful part of the identification process should you find one of these.

Male catkins of native Black Poplar. The male catkins of black and hybrid poplars are red due to the colour of the pollen-bearing anthers. Poplars have the annoying habit of growing tall and flowering towards the top of the tree, but the difference between male and female catkins can be told with binoculars or by looking for fallen catkins on the ground.

Close up of a female catkin of Populus x canadensis 'Regenerata' - a widely-planted variety in East Anglia. Each bract has a whiskered fringe and has beneath it a swollen, whitish stigma, sticky and waiting to receive wind-blown pollen.

Close up of a male catkin of Populus x canadensis 'Robusta', a spreading, imposing cultivar. Beneath each fringed, whitish bract can be seen a cluster of purple-red anthers full of pollen.

The Goat Willow or Great Sallow (Salix caprea) is a common native of damp woodland and also widely planted. It is one of several shrubby willow species that is referred to as 'Pussy Willow' when the catkins first emerge, covered in silky hairs. Here, the yellow male anthers have now pushed through the silky hairs and changed the appearance of the flower head.

Female catkins of Grey Willow or Grey Sallow (Salix cinerea). Female willow catkins tend to appear narrower than the catkins of male plants as they don't have anthers that need to be pushed out into the wind. Here you can see that the silky flower head is studded with pale, greenish stigmas.

Just to show some willow variety, here's the more slender male catkin of Purple Willow (Salix purpurea), a less common species than the other sallows above, but still fairly frequent in Broadland and parts of Breckland.

If you are into solitary wasps and their intriguing life-styles, catkins can provide plenty of entertainment. These swollen lumps are not fruits, but galls, caused by the presence of tiny cynipid wasps that lay their eggs in the flower clusters and leave their larvae to develop inside. These galls are on the male flowers of a large Lucombe Oak (Quercus x crenata) in Earlham Road Cemetery, Norwich - a place where I shall be leading a tree walk later in the year!