Flat-leaved willow  (Salix planifolia)

The flat-leaved willow has not yet been assessed by the IUCN.

A fast-growing, characteristically shrubby species (2), the flat-leaved willow (Salix planifolia) is a distinctive perennial plant with smooth, grey bark (3) (4). The branches are yellow-brown, reddish-brown, dark brownish or violet, and may be hairless, or with a covering of short or long hairs. The branches are occasionally coated in a whitish, waxy bloom (2) (3) (5). The smaller branches may also be hairless, or with a soft covering of fine or dense, short, silky hairs (2) (5).

The flat-leaved willow has narrow, oblong-shaped leaves which are dark glossy green and usually hairless on the upper surface, and whitish below, sometimes with a white, waxy coating and a sparse covering of white or reddish, silky hairs (2) (3) (4) (5). The margins of the leaves are typically smooth, but they may also be slightly serrated or with small, rounded teeth (2) (5). The juvenile leaves of this species are usually reddish or yellowish-green (2).

The flat-leaved willow produces long, cylindrical, dense clusters of yellow-green flowers, called ‘catkins’, before the leaves emerge (2) (4) (5). The male catkins are one to four centimetres long and between 1 to 1.5 centimetres wide, and are usually stout and almost rounded. The female catkins are longer, reaching up to around six centimetres, and usually appear much slenderer than the male catkins (2). The catkins are initially compact, becoming fuller and fluffier throughout the flowering period (4).

A wide ranging species, the flat-leaved willow occurs from southern Yukon to Labrador in Canada, and south to Maine, New Hampshire, Vermont, Wisconsin, Minnesota and several other areas in the northern United States (3) (5) (6) (7). It is largely restricted to mountainous terrain in the United States, especially in the western parts of its range, where it occurs as far south as California and New Mexico (3).

The flat-leaved willow inhabits wet mountain meadows, stream and lake edges, swamps, marshes, bogs and fens. It may also occur in woodland openings (3) (4) (5) (6) (7).

The flat leaved-willow is generally found at high-elevations in upland or mountainous regions (3) (5) (6), but may occur at any elevation between 100 and 4,000 metres (5).

The flat-leaved willow usually produces catkins between May and June (5) (8), and begins fruiting from around June (8). It is dioecious, with the male and female flowers occurring on different plants (2) (4). At the base of each flower, there are one or two small glands which secrete sweetly-scented nectar to attract insects, particularly bees and moths, to pollinate the flowers (9). After the flowers have wilted, the male catkin dries up, while the female catkin turns green and lengthens as the fruit develops (4).

The small, capsule-like fruits of the flat-leaved willow contain an abundance of small, light-weight, cottony seeds, which the plant begins to produce at around two years old. When the fruit reaches maturity, it splits open and releases the seeds, which are dispersed by the wind and water (3) (4). The whole catkin may be shed when the seed is ripe, which often results in cottony drifts forming under the willow plant in late spring (9).

Very few threats to the flat-leaved willow have currently been identified, although hiking and recreational use is thought to pose a potential risk to populations of this species in some areas (6).

There are currently no conservation measures targeted specifically at the flat-leaved willow.

Recommended conservation actions include protecting this species’ habitat from natural disturbances and changes in water regimes along streams, river and lakes (10).

Find out more about the flat-leaved willow:

• Flora of North America:
  http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=242445830
• Maine Department of Conservation, Rare Plant Fact Sheet - Salix planifolia:
  http://www.maine.gov/doc/nrimc/mnap/features/salix_planifolia.pdf