Willows of New England

Salix atrocinerea: identification in winter

Salix atrocinerea is treated differently by different authors, and our treatment may not necessarily be the same as in other keys. Besides, our study is only based on populations in New England: variabilty and range of characters of the willow we treat here as S. atrocinerea may not be the same as in the area of its natural distribution in Subatlantic Europe. One should not think either that 'pussy willows' introduced from Europe had been wild collected; on the contrary, originally introduced plants apparently included cultivars and cultivated hybrids. Its hardly possible to tell now which of them were able to escape from cultivation. We cannot even tell whether the willows in question are actually products of subsequent hybridization with native willows.

Difficulties with willow identification have been probably somewhat exaggerated. Assuming that one cannot mix willows with other plants and would not confuse willows belonging to different subgenera (that is, separate S. babylonica, S. alba, and S. nigra from the rest of the willows), we hope that the proposed illustrated list of characters will help identify invasive populations of S. atrocinerea right in the field and even during the wintertime. While we don't think that this is going to be enough to correctly and reliably identify each specimen, we hope that this is enough to recognize any well-established population of S. atrocinerea in most cases.

  1. If not damaged, mostly grows as a tree 10 or even 15 m tall.

    (Of the New-England willows belonging to the subg. Vetrix, S. bebbiana can grow as a tree, as well. Tree growth is also characteristic of S. caprea, and, as a rare exception, of S. aurita; however, the latter two are known in cultivation only and hardly ever become naturalized in our area.)

  2. Dense and long ridges are formed on the wood underneath the bark. They correspond to longitudinal furrows on the bark surface of branches that are a few years old. This wavy structure might be distinct even on the trunks of older trees, in their upper parts.

    (This character is shared with Salix cinerea, but that species never grows as a tree, as far as we know. In Salix aurita, S. caprea, and S. bebbiana, ridges are either completely absent or short and sparse; the corresponding type of bark is never formed.)

  3. Floriferous buds are very large and different from vegetative buds--both in their shape and size.

    (Such bud shape is characteristic of most species of sect. Vetrix sensu str. (= Vetrix subsect. Laeves): S. caprea, S. cinerea, S. aurita, and the native S. discolor; it should separate this willow from more distantly related S. bebbiana (sect. Fulvae = subsect. Substriatae of sect. Vetrix.) See drawing of S. starkeana from Skvortsov (1955).

  4. Shoots are rather slender, usually about 1-2 (2.5) mm thick. Shoots and buds are frequently with reddish coloration and glabrous.

    (In this character, S. atrocinerea would remind the rarely cultivated S. aurita as well as the native S. bebbiana; this should distinguish it from the native S. discolor and introduced S. cinerea, both of which should have much thicker and, at least in case of S. cinerea, entirely gray-colored shoots and branches.)

S. caprea

S. cinerea

S. aurita

S. starkeana

In case one finds that in the studied specimens the characters match this list, he might conclude he deals with S. atrocinerea. If not, the population probably should be examined once again during the summer season. Perhaps, tree habit is not obligatory for S. atrocinerea. Therefore, in the wintertime we cannot reliably identify shrubby populations.

1 Feb 2007 (A. Zinovjev & I. Kadis)