Willow Explorers - Glossary

Compilation Pol Meert

with thanks to Joost Verbeke, Jan De Langhe Arboretum Wespelaar, Sonja Deneve

for the corrections and many suggestions

Glossary

Tree or shrub?

Tree: at maturity, a tree has an unbranched main stem (trunk) of at least 1 metre in height.

Shrub: without a main stem or if the stem branches at a height of less than 1 metre.

Cultural willows

All taxa that were used for basketry, ornamental cultivation, or other purposes; they were either brought in from abroad or deliberately crossed or bred.

When Willow Explorers does not yield a determination, one can use Arnout Zwaenepoel's Willow Key:

Zwaenepoel, A. (2018). Sleutel voor de in het wild en verwilderd voorkomende wilgen in de lage landen. Soorten, ondersoorten, kruisingen en cultuurvariëteiten. WVI, 113 p.

Glossary to the key by Arnout Zwaenepoel, partly edited for this website

Hairiness. The hairiness of willow leaves is a commonly used feature in determination, but shows considerable variation throughout the season. Very young leaves are almost always slightly hairy, even if they go bare very quickly. The hairiness of normally very hairy leaves (White willow, for example) may nevertheless decrease considerably towards the end of the season (October). Hairiness therefore remains a relative characteristic. It is always advisable to include other characteristics in the determination. A loupe magnified 10 to 15 times is recommended to test the hairiness characteristic.

The method of viewing the hairs is important. With a leaf, top or bottom, it is always best to look at the hairiness from the leaf base towards the leaf tip. Then the hairiness, if there is any, is best viewed and assessed.

Frosted. Some willows have a layer of glaucous wax on the leaves or branches. This often gives rise to a whitish or bluish appearance. In leaves, the wax layer is usually on the underside of the leaves (Crack willow, Almond willow ...). When a wax layer occurs on branches, it is usually situated at the top of young branches (Europea violet willow, Caspian sand willow).

Bifurcate. Branching into two (more or less equal) parts. Forked. Used in key for the branched catkins of Crack willow

(Salix x fragilis) var. furcata.

Clone. In general, a clone means a more or less identical duplicate of something. In biology, one speaks of cloning for genetically identical specimens. The verb for this process is also called cloning. Specifically in willow, it involves vegetatively propagated cuttings from one parent plant. Both in the selection of wicker willows and ornamental willows, cloning is a very common practice, to preserve a particular characteristic. The phenomenon is also very common in pollarded willows on the edge of meadow plots, albeit usually not to promote a particular characteristic, but simply because cloning is a simple method of propagating from a single parent

Clone group. A range of cultivated varieties of willow are so similar that they are difficult to distinguish individually on appearance alone. Nevertheless, they can be distinguished from other groups on the basis of certain characteristics. Especially in Almond willow/S. triandra, a number of distinct groups can be distinguished, based on the twig colour of annual twigs (dark chocolate-brown, coffee-with-milk-brown or yellow-green). These groups are referred to as clonal groups in the key.

Short-lot. Generally a branch with closely packed nodes. Used in the willow key mainly when designating 'common' branches with 'common' leaves, to distinguish them from 'langlots', which are described below and have some different characteristics.

Longleaf. Annual shoot with deviating characteristics from normal branches. Usually a long shoot is fast-growing, low-branched and often coloured differently from the other branches. The leaves on a long shoot also often differ from the normal leaves. Fast-growing leaves can all show undulation, in numerous willows. Leaf undulation should certainly always be related to the age of the leaf and to short or longshoot. The normal descriptions refer to short shoots leaves and not long shoot leaves. Long shoots are stimulated by pollarding, or in the annual harvesting of twigs in shrub cultivation.

Striae. A number of willows have conspicuous elongated structures under the bark that are visible as ridges measuring from a few millimetres to several centimetres. The Grey willow (S. cinerea) is the easiest willow to learn about the structures. To see these so-called 'striae' (in botanical literature), it is best to take a two- or three-year-old twig (but striae can usually be seen on annual or older twigs too). The bark can easily be peeled off a piece of twig about 10 cm long during the vegetation season. Later in the season, from August when the sap flow decreases, this is more difficult. The striae and their length are a very important feature in the determination of a lot of willows. In the literature, the characteristic is often treated somewhat casually. Small striae of 1 to 2 mm, which do occur in most species in the vicinity of nodes (branch or leaf apex) are often not mentioned or not considered to be striae. Only when the striae are 5 mm or longer, they are mentioned. An attempt is made here to always mention this feature very clearly. However, the variation within length and number of leaflets is considerable, so that this feature can and should rarely be used as the only one.

Subspecies. Indicated here as ssp. (subspecies).

Photos: De Wilgenzoeker = Willow Explorers