Salix fragilis L.
crack willow
Tree to 25 m high, sometimes only a shrub; bark rough and fissured. Branches spreading but not pendulous. Shoots dark or brownish green, readily snapping with an audible crack when bent, not slender. Bud scales dark shining brown, becoming glabrous. Shoots and lvs somewhat silky when very young, but quickly glabrous. Petiole of lvs on reproductive shoots < 1 cm long. Lamina 5-15 × 1-2.5 cm, sometimes larger on water shoots, lanceolate, glaucous beneath, ± shining above, glandular-serrulate; apex acuminate. Stipules minute. Catkins usually ♂, rarely ♀, appearing with or after lvs. ♂ catkins 4-7.5 cm long, spreading or curving downwards, narrow-cylindric; rachis villous. Bracts 2-2.5 mm long, oblong-elliptic, incurved and ± cucullate when fresh, pale green or yellowish, densely clothed in antrorse hairs; apex rounded. Glands 2, 0.4-0.6 mm long, elliptic-oblong, rectangular to square. Stamens 2; filaments hairy towards base. ♀ catkins similar to ♂. Ovary glabrous, sessile or shortly stalked.
N.; S.; St.; Ch.: widespread and often abundant throughout.
Europe and W. Asia 1880
Waterways, ponds, lakesides and other wet habitats.
FL Sep-Oct.
Crack willow was introduced in the early days of European settlement. Within 15 years or so it began to cause problems in some E. coastal areas of both main islands; the brittle, easily broken shoots grow extremely easily and consequently they soon began to block streams, drains, and culverts. Since then crack willow has been a much greater nuisance in N.Z. than any other willow. Presumably, one or a very few introductions were made because today nearly all the trees are ♂ and probably belong to a single clone. However, S. fragilis has frequently crossed with the widespread ♀ form of S. alba var. vitellina (see S. × rubens), and some of the progeny may have backcrossed with S. fragilis. Such backcrosses are very like S. fragilis in lf hairiness, whilst the shoots vary in brittleness but tend not to make the audible crack that the ♂ parent does when broken. Hybrids are almost certainly commoner than has been realised, particularly in areas where typical S. alba var. vitellina occurs. S. fragilis also forms hybrids with S. babylonica (see S. × pendulina under S. × sepulcralis). Records of S. alba naturalised in the North Id in the 19th century are mostly based on misidentification of S. fragilis.
Two features prominent in most crack willows are the mass of bright red rootlets formed when major roots are in or near water, and the bright red galls of willow sawfly, Pontania proxima (Leperletier), on the upper lf surfaces. This redness is present to some extent in the hybrid S. × rubens, whereas in true S. alba the rootlets are whitish and the sawfly galls pale greenish. Less diagnostic, but a prominent character of S. fragilis and its hybrids in spring are the caducous small lvs at the shoot bases.
