Willows of New England

Comparison of introduced species Salix atrocinerea and S. cinerea

The two willows are very closely related and sometimes treated as two subspecies of a single species. Salix cinerea is native in most of Europe and West Siberia, while Salix atrocinerea (=S. cinerea ssp. oleifolia) has Mediterranean and South-European Atlantic distribution type. We are inclined to treat them as distinct species following A. Skvortsov and many other authors. Both willows have been naturalized in Massachusetts, though gray willow, S. cinerea seems to be less common.
Though it might be difficult to identify dry samples, in nature these willows look quite different from each other. The situation with them reminds us the problem of distinguishing between Eurasian Salix viminalis and S. burjatica (=S. dasysclados): There are many distinguishing characters, but all of them vary in such a way that their extreme values overlap. However, ... both species are distinct, and it is always possible to distinguish between them when there is enough of perfect, complete samples (Skvortsov 1968: 59, 1999: 64). The only way to deal with this situation is to use a combination of characters in the identification key and species diagnoses (Skvortsov 1968: 58, 1999: 63).
There exists a possibility that the European willows have produced hybrids with native species and/or with each other, but there is no direct evidence of that as of today.

Salix atrocinerea

Salix cinerea

A single-trunk tree up to 10(15) m tall when undisturbed.
Sometimes may grow as a shrub.
A multi-stem shrub, sometimes rather tall, up to 5-6(7) m.
Never grows as a tree.
Mother Brook at Turtle Pond Pkwy, Boston Mother Brook at Turtle Pond Pkwy, Boston Mary Dunn Pond, Hyannis
Branches frequently yellowish to reddish, pubescence rather loose and may promptly disappear. Floriferous buds in autumn usually red and glabrous. Young shoots much slenderer than in gray willow. Upper leaf surface usually bright green and shiny. Leaf shape variable with some leaves widest above the middle, others at about the middle. Branches and buds grayish with dense persistent pubescence; young shoots stout. Leaves rather dull, with maximal width distinctly above the middle, gradually attenuating toward base.
Ames Nowell State Park, Abington Mary Dunn Pond, Hyannis
Mary Dunn Pond Mary Dunn Pond, Hyannis
Lower leaf surface pubescent to completely glabrous, characteristic ferrugineous hairs may be present or absent. Lower leaf surface with grayish pubescence, ferrugineous hairs, according to literature data, always completely absent.*
Hyannis Mary Dunn Pond, Hyannis
  *Once, late in autumn, we observed intensive ferrugineous coloration on lower surface of nearly dead leaves, but it appeared to orignate from gland excretions and produce a false impression of hairs tinted reddish.
20 Nov 2006 (A. Zinovjev & I. Kadis)