Flora of New Zealand Series

Trees with pale, ± furrowed bark. Winter buds with several imbricate scales. Lvs alternate; petiole usually long; stipules inconspicuous, caducous; lamina lanceolate-ovate to broad-ovate or deltoid, sometimes lanceolate in juvenile lvs, entire or dentate. Catkins pendulous, appearing before lvs. Fls anemophilous, each subtended by a bract; bract usually laciniate or toothed, rarely entire, quickly shrivelling. Perianth reduced to a cupular, oblique disc; glands 0. ♂ fls with 4-many stamens; filaments ± filiform; anthers generally red to purple, occasionally yellow. ♀ fls with short style; stigmas 2-4. Capsule 2-(4)-valved, often ripe before lvs are fully mature. Seeds numerous, minute.

c. 30 spp., N. temperate regions. Naturalised spp. 6 and 3 hybrids.

Poplars have been abundantly planted throughout settled areas of N.Z. because, except for spp. of sect. Leucoides Spach., they are easy to propagate and grow quickly. They have been extensively used for windbreaks and erosion control, and to a lesser extent as ornamental trees. A range of spp. and hybrids are cultivated; hybrids are now particularly prominent because of intensive selection of suitable clones to replace the P. nigra cvs and hybrids which have succumbed to poplar rusts (Melampsora larici-populina and M. medusae) in recent years. Although poplars rarely become naturalised as commonly as some willows do, several spp. and hybrids are described here because they often appear fully naturalised when they are only wild to a very minor extent. This is because they have been planted amongst scrub and similar vegetation beside rivers, lakes and other waterways and have become naturalised nearby. In very few instances have populations arisen naturally from seed, in fact some spp. are represented in N.Z. by only one sex.

In the following descriptions lf measurements do not account for the very large lvs with very long petioles which are often produced on strong, ± juvenile, sucker and water shoots. Within adult branches there is sometimes a difference in lf shape, as lvs on the long extension shoots tend to have more rounded to cordate bases than those on short side or spur shoots. The time of appearance of the young lvs is diagnostic and the same sequence of lf flushing occurs among the various poplars whether the season is early or late. Fls of most naturalised poplars are illustrated in Figs 104 and 105.

Fig. 104. Populus, ♀ fls. A P. alba; B P. deltoides; C P. × gileadensis. © All rights reserved. [Image: 4X3H]

Fig. 105. Populus, ♂ fls. A P. nigra cv. 'Italica'; B P. tremula; C P. trichocarpa; D P. yunnanensis. © All rights reserved. [Image: 4X3I]