Habit and leaf form. Trees and shrubs (and subshrubs); leptocaul. Helophytic, or mesophytic. Heterophyllous (in some Populus species), or not heterophyllous. Leaves deciduous; small to large; alternate; spiral to distichous; flat; petiolate; non-sheathing; simple. Lamina entire; pinnately veined; cross-venulate. Leaves more or less exstipulate (Chosenia), or stipulate (usually). Stipules intrapetiolar; free of one another; caducous (often), or persistent. Lamina margins entire, or serrate, or dentate. Vegetative buds scaly. Leaves without a persistent basal meristem. Domatia recorded (Populus); represented by hair tufts.
Leaf anatomy. Mucilaginous epidermis commonly present.
Adaxial hypodermis present, or absent. Lamina dorsiventral (usually), or isobilateral. Minor leaf veins without phloem transfer cells (Salix).
Stem anatomy. Young stems cylindrical. Cork cambium present; initially superficial. Nodes tri-lacunar. Cortical bundles absent. Medullary bundles absent. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. The secondary phloem stratified into hard (fibrous) and soft (parenchymatous) zones, or not stratified. `Included' phloem absent. Xylem with libriform fibres; with vessels. Vessel end-walls simple. Vessels without vestured pits. Primary medullary rays narrow. Wood parenchyma apotracheal (exclusively terminal). Sieve-tube plastids S-type.
Reproductive type, pollination. Dioecious. Anemophilous, or entomophilous.
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in `inflorescences'; in catkins. The terminal inflorescence unit racemose. Inflorescences axillary (or precocious); catkins; pseudanthial, or not pseudanthial. Flowers individually bracteate; ebracteolate; minute to small. Free hypanthium absent.
Perianth absent, or vestigial (represented by a cupular disk or by small nectariferous scales).
Androecium 2-30. Androecial members free of one another, or coherent; when coherent 1 - adelphous. Androecium exclusively of fertile stamens. Stamens 2-30. Filaments not appendiculate. Anthers basifixed; dehiscing via longitudinal slits; tetrasporangiate. Endothecium developing fibrous thickenings. Anther epidermis persistent. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral, or isobilateral, or decussate. Anther wall initially with one middle layer, or initially with more than one middle layer; of the `monocot' type. Tapetum glandular. Pollen grains aperturate, or nonaperturate (Populus); when aperturate, (2-)3(-6) - aperturate; colporate (colporoidate); 2-celled.
Gynoecium 2(-4); syncarpous; synstylovarious; superior. Ovary 1 locular. Stigmas 2-4. Placentation basal, or parietal. Ovules in the single cavity 20-100 (i.e. `many'); funicled (the funicle becoming silky-hairy); ascending; anatropous; unitegmic, or bitegmic (when the inner integument is weakly developed); crassinucellate. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral. Synergids with filiform apparatus. Endosperm formation nuclear. Embryogeny onagrad, or asterad.
Fruit non-fleshy; dehiscent; a capsule. Capsules 2-4 valvular. Seeds scantily endospermic, or non-endospermic. Endosperm when present, oily. Cotyledons 2. Embryo chlorophyllous (2/8); straight.
Seedling. Germination phanerocotylar.
Physiology, biochemistry. Cyanogenic (?), or not cyanogenic. Alkaloids absent (usually), or present. Iridoids absent. Proanthocyanidins present, or absent; when present, cyanidin, or cyanidin and delphinidin. Flavonols present; kaempferol and quercetin. Ellagic acid absent (2 genera, 8 species). Arbutin absent. Saponins/sapogenins absent. Aluminium accumulation not found. Sugars transported as sucrose. C3. C3 recorded in Populus, Salix. Anatomy non-C4 type (Populus, Salix).
Geography, cytology. Frigid zone and temperate. Absent from Australasia and New Guinea, otherwise cosmopolitan, but mostly temperate Northern hemisphere. X = 11, 12, 19.
Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren's Superorder Violiflorae; Salicales. Cronquist's Subclass Dilleniidae; Salicales. Takhtajan's Subclass Dilleniidae; Dillenianae; Salicales. Species 350. Genera 4; Salix, Populus, Chosenia.
Economic uses, etc. Many are cultivated as ornamental trees and shrubs, and Salix contributes timber (notably for cricket bats) and withy twigs for basketry.
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