This very variable crack willow hybrid is a cross between white willow (S.alba) and crack willow (S. euxina) over many generations, and back-crossings with the parent species. Individual trees vary in habit, in height, in the colour of their shoots and in the shape of their leaves. In fertile moist places they grow into large broad-crowned trees in some ways resembling the oil trees of southern lands.
The luxuriant foliage of this hybrid crack willow is narrow-leaved, shiny and dark green, with a bluish-grey underside. The shoots are usually dark brown but can also be yellow- or red-brown, or even bright red or yellow. They are quite fragile, and if pieces fall into water they can begin to grow roots, producing new trees.
This willow has spread almost wherever people are to be found. In some ways they tolerate man-made environments better than the white willows. The specimen in the Arboretum, when originally planted in 1914, was identified as crack willow (S. fragilis) and is still to be found where Pähkinärinne (Hazelnut Slope) borders on a field. After storm damage it was severely cut back, which gave it a new lease of life with new growth. The two trees growing between the “Piika ja Renki” Café and the main highway are probably slightly younger, and of different origin. They seem to suffer from a fungus which blackens their shoots.