Salix herbacea L.*

Abstract

Salix herbacea is the smallest of the British willows. It is a dioecious, prostrate, dwarf shrub with an extensive ramifying system of tough, branched, underground rhizomes, forming loose, flattened mats. Aerial branches short (up to 5 cm above the soil surface, but occasionally 10 cm), thinly pilose, soon becoming glabrous, dark shining brown or reddish (Meikle 1984). Shoots are distinguishable from rhizomes because the former are segmented by bud-scale scars. Leaves 6-20 mm long, but very variable in size, orbicular or broadly ovate or obovate, rounded or retuse, base rounded or subcordate or very broadly cuneate; margins crenate-serrate or rarely entire; apex rounded or shallowly emarginate, occasionally subacute; thinly white-pilose above and below at first but soon becoming glabrous, bright green and shiny, venation prominently reticulate on both sides. Petioles very short, usually 3 mm long and 2 mm wide, at first thinly hairy or subglabrous but soon glabrous (Meikle 1984). Catkins appearing with the leaves in June and July (or as late as August at high altitudes), inconspicuous (usually < 12-flowered), commonly terminal on short branches, subsessile or with hairy peduncles up to 8 mm long (range 515 mm); bracts wanting. Catkin scales nearly obovate, yellowish-green, sometimes reddish on margins, glabrous or thinly pubescent, oblong or obovate, 1-2 mm long, 0.5-0.8 mm wide. Male catkins with two free stamens; filaments glabrous, 2-3 mm long, yellow or tinged red; nectary variable, commonly cup-like and deeply lobed surrounding the bases of the filaments or sometimes consisting of one or two entire or lobed, distinct nectary scales. Female catkins more conspicuous than male; ovaries narrowly flask-shaped, glabrous or rarely with a few hairs, sessile or very shortly stipitate, 2-3 mm long, 1 mmii wide, often turning vinous-red with age; style short (0.5 mm) but distinct; stigmas short (0.2-0.4mm), spreading, deeply bifid; nectaries one or two, oblong and entire or irregularly lobed (Meikle 1984). Capsule reddish purple, up to 8 mm long (normal range 3-6 mm) and 3 mm wide, glabrous, often reddish, subsessile, lanceolate. Each seed 0.9-1.8 mm long and 0.25-1.0 mm wide. Air-dry seed mass 66-136 ig (mean + SE = 92.8 + 3.4 ,g) (ii = 75). Native to the British Isles, S. herbacea is frequently common in parts of the Scottish Highlands, local in the Lake District in England, but is more restricted in Wales and western Ireland (Fig. 1). In the high arctic, S. herbacea occurs in late-melting snow-beds, hill slopes and stony-gravel plains. In their new geographical classification of British and Irish vascular plants, Preston & Hill (1997) group S. herbacea into their European arctic-montane element. Salix herbacea belongs to Hulten's Amphi-Atlantic category, with a wide arctic-montane distribution in Europe and North America, reaching westernmost (arctic) Asia, but is absent from the Pacific region (Atl. Fl. Eur.; Atl. N.W. Eur.; Meikle 1984; Hulten & Fries 1986).