SALICACEAE (Willow Family)

Plants shrubs or more commonly small to large trees, dioecious, sometimes colonial from root suckers or stem fragmentation. Leaves alternate (rarely opposite or whorled in Salix purpurea), short- to long-petiolate, sometimes with glandular dots or short, conical, toothlike glands along the petiole or at the blade base. Stipules usually present (sometimes minute), herbaceous, sometimes fused around the stem along 1 margin, often shed early. Leaf blades simple, unlobed (5-lobed in Populus alba), pinnately veined with a single, well-developed midvein or with 3(5) main veins, the margins finely to coarsely toothed, the teeth usually minutely gland-tipped. Staminate and pistillate inflorescences on separate plants, often flowering before the leaves develop, consisting of solitary, more or less dense catkins (inflorescence type and position variable elsewhere), these terminal on short branches or appearing axillary, each flower subtended by a small bract, this sometimes shed early. Flowers imperfect, technically hypogynous, but the perianth highly reduced to a small, flat to cup-shaped disc (in Populus) or 1 or 2, fringed and sometimes irregularly lobed or fused nectaries (in Salix). Corollas absent. Staminate flowers with the stamens (1)2 to numerous, the filaments free or variously fused, slender, the anther attached at its base, purple or yellow; lacking a vestigial pistil. Pistillate flowers with the ovary superior, sessile or short-stalked, composed of 2–4 carpels, 1-locular, with 2 to numerous ovules, the placentation parietal; staminodes absent. Style 1, usually with 2(–4) minute branches toward the tip, occasionally very short or apparently absent, the stigmas 2(–4), variously shaped. Fruits capsules, dehiscent most of the way from the tip by 2–4 persistent valves. Seeds 0.8–3.0 mm long, narrowly oblong in outline to ovoid, green to reddish brown, surrounded by a dense tuft of long, silky hairs attached at the seed base. Traditionally two genera, about 450 species (but see discussion below), nearly worldwide (but absent from Australia and Malaysia), most diverse in the northern hemisphere.

Traditionally, the family Salicaceae in North America was treated as comprising only 2 genera, Populus and Salix, with about 450 total species (Steyermark, 1963, Cronquist, 1981, Gleason and Cronquist, 1991). However, molecular studies have shown that the members of several tropical families, notably portions of the Flacourtiaceae, should be considered part of the Salicaceae in order to circumscribe a natural group (Savolainen et al., 2000, Soltis et al., 2000; Chase et al., 2002). This results in an enlarged family of nearly worldwide distribution that includes about 58 genera and more than 1,200 total species, although the exact limits are still under study (Chase et al., 2002; Alford, 2006). The familial description above focuses on the Missouri representatives (which are included in the tribe Saliceae within the broadly conceived family), in order to maximize the usefulness of the treatment for determination of Missouri specimens. Some of the discordant characters of the more tropical genera include: perfect flowers that occasionally are not hypogynous and are organized into in a variety of different inflorescence types; presence of 3–8 or more unmodified sepals, these distinct or fused basally; presence of 3–8 or more small petals; in some genera the presence of staminodes among the stamens; fruits variously berries, capsules, or drupes; and seeds commonly hairy or with an aril, but lacking the tuft of long hairs (the coma) that is characteristic in Populus and Salix.

The two Missouri genera of Salicaceae contain numerous species that are prized horticulturally as shade and specimen trees, as well as for wind breaks, erosion control, and revegetation of highly impacted sites, such as mines and quarries. Some of the species also are used commercially for lumber, fence posts (including living fences), pulp for paper, handcrafts, and medicinally.