Salix

Salix is a difficult genus that displays tremendous phenotypic plasticity. Though hybridization does occur (and can be occasional between some species pairs), most aberrant forms are the products of environmental and seasonal variation rather than interspecific crossing. Therefore, not all hybrid combinations that have been reported are included here until further research confirms their identities. Early season leaves usually possess denser indument than later season leaves. Some species often produce red-brown hairs, which, when present, are very useful identifying characters. However, all species that produce such hairs can lack them altogether. The leaves that emerge from the buds are called first leaves (or preformed). As the branchlet continues to grow it produces additional leaves called new leaves (or neoformed). It is important to distinguish between these two types as they can differ morphologically, especially in the prominence of stipules. To assist with identifying features of the branch wood surface (decorticated branches), be sure to remove the bark when specimens are fresh, otherwise the bark adheres to the wood and becomes difficult to remove. Some species of Salix have brittle-based branchlets that break ± cleanly at the junction of annual growth. Other species have flexible-based branchlets that partially break and then must be torn 
free from the branch. This character (branch brittleness) is very useful for identification and 
is important to note on herbarium labels. Salix trianda L. was reported from ME by Argus (2010). However, the determination is qualified as “probably,” and the tree was originally determined as S. amygdalina L., a species planted in the former Fay Hyland Arboretum (University of Maine). Reports of Salix ×‌smithiana Willd. from MA (Sorrie and Somers 1999) 
and ME (Campbell et al. 1995) were based on collections of S. ×‌sericans (see discussion under that nothospecies). References: Argus (1986), Meikle (1984).