Flora of New Zealand Series

Trees or shrubs, sometimes prostrate and rooting at nodes; bark rough and fissured or smooth. Winter buds with 1 outer scale. Lvs usually alternate, rarely opposite, entire or shallowly toothed; petiole usually short; stipules sometimes 0 or inconspicuous, sometimes conspicuous, usually caducous, especially on strong vegetative shoots; lamina generally lanceolate or elliptic to obovate, often with glandular margin. Small lvs often present at base of lateral shoots. Catkins erect or pendulous, appearing before, with, or after lvs. Fls entomophilous, each subtended by an entire bract. Perianth reduced to 1-2-(4) glands, more rarely these united to form a basal semi-annular lobed ring. ♂ fls with (1)-2-(12) stamens; anthers usually yellow, sometimes red. ♀ fls with 1 short or very short style and 2 stigmas. Capsule 2-valved, usually maturing well after lf maturity. Seeds nearly always numerous, very small or minute.

c. 300-500 spp., N. temperate regions, few S. to the Andes and South Africa. Naturalised spp. 11 and 5 hybrids.

Spp. of Salix, willows, were introduced to N.Z. during the earliest period of European settlement and their attractive appearance, ease of vegetative propagation, and the rapid growth of most spp., ensured that they were soon very widely distributed. The spread of willows was so rapid that on occasions the first Europeans entering an area found willows already there, and by the beginning of the 20th century willows already occupied a place in Maori culture. Since then, except in tussock grasslands and remaining areas of indigenous forest, willows have become so much a part of the N.Z. scene in all modified lowland and submontane regions that it is difficult to imagine the countryside without them. Thus, riverbanks, lakesides, drainage channels, swamps and almost all wet places, now frequently support a vegetation dominated by Eurasian spp. and hybrids of Salix comprising sallows, osiers, crack and white willows. Their role in stabilising the banks of waterways has been of great importance in helping to prevent floods and they have been used to prevent erosion in other habitats as well. Conversely, their rapid growth and free-rooting habit has resulted in the choking of waterways and the invasion and domination of swamps. This deleterious aspect began to manifest itself within 2 decades of the original introductions.

Since the Second World War, willows have been systematically introduced for evaluation of their potential usefulness by the Soil Conservation Centre, D.S.I.R., now at Aokautere, Palmerston North. Some have subsequently been released to catchment boards for planting in their particular regions. In addition to those described, several prostrate or semi-prostrate spp. are on trial for suitability in colonising high country screes and similar habitats, and osiers other than S. viminalis are being increasingly grown for basketry. Canterbury, Poverty Bay, and the Manawatu, were the main areas of introduction this century.

The taxonomy of many of the spp. is very complex because of the large amount of hybridisation here as well as in their countries of origin. Dioecism is another factor complicating willow taxonomy; in N.Z. most spp. are represented by only one sex, in certain instances by probably only one clone. Recently there has been a deliberate attempt to try and keep the sexes of one sp. apart in cultivation, or to introduce only ♂ plants, because of the added weed problem of freely seeding plants.

Notes on identification

The spp. and hybrids described here include all those which occur commonly in wild habitats such as riverbanks, swamps, and lakesides, whether they are truly wild or whether in some cases they may have been originally planted but this is no longer evident.

The descriptions have been mostly drawn up from fresh material. This is because colour of vegetative parts and catkin bracts, shoot brittleness and appearance below the bark, lf taste, habit of the tree or shrub, and appearance of the catkin glands, are all best seen in live plants. Lf measurements and stipule comments do not always embrace the very large lvs sometimes occurring on strong sucker, water, or coppice shoots. Likewise the small prophylls often found near the base of shoot laterals are excluded from the figures. A key based on vegetative characters only has been included because the catkins, especially ♂, are very ephemeral. It is impossible to encompass every hybrid in either key because of the many different crosses and back-crosses that may occur when several spp. grow together. This is particularly true of osiers, sallows and bitter willows, between which almost any hybrid combination may occur. Within the tree willows, hybrids also occur freely. Fls of most naturalised willows are illustrated in Figs 106 and 107.

Fig. 106. Salix, ♀ fls. A S. alba; B S. babylonica; C S. cinerea; D S. elaeagnos, E S. purpurea; F S. × calodendron; G S. × chrysocoma; H S. glaucophylloides; I S. × sepulchralis; J S. viminalis. © All rights reserved. [Image: 4X3J]

Fig. 107. Salix, ♂ fls. A S. alba; B S. fragilis; C S. × reichardtii; D S. viminalis; E S. cinerea; F S. daphnoides subsp. acutifolia; G S. × chrysocoma; H S. purpurea. © All rights reserved. [Image: 4X3K]