Flowering Plants: Willows to Mustards

Descriptions and Illustrations

Descriptions and Illustrations Order Salicales The Salicales includes only the family Salicaceae. In the Thorne system of classification (1968), the Salicales is one of four orders comprising the superorder Cistiflorae. The other orders are the Cistales, Tamaricales, and Capparidales. Cronquist (1968) accords similar treatment, but recognizes the name Violales instead of Cistales (including within it the Tamaricales). Even though the Salicales seems isolated from all other plant groups, Thorne and Cronquist both agree that it represents advanced derivatives of a cistalian or violalian ancestor, primarily on the basis of the compound, unilocular pistil with usually parietal placentation. Brown (1938) had earlier suggested a relationship among the Cistales, Salicales, and Capparidales on the basis of similar nectaries. The earlier idea that the Salicales is very primitive has been refuted by most botanists today. Only the following family comprises this order. SALICACEAE - WILLOW FAMILY Trees or shrubs, mostly dioecious; leaves simple, alternate (rarely nearly opposite), with stipules; flowers unisexual, arranged in catkins , without a perianth; staminate flowers each subtended by a bract and either a cupular disc or 1-2 glands, with 2 to several stamens , the filaments free or connate at the base, the anthers 2celled , with vertical dehiscence; pistillate flowers each subtended by a bract and either a cupular disc or 1-2 glands, with one pistil, the ovary superior, unilocular, with 2-4 parietal placentae and numerous ovules, the style with 2-4 stigmas; fruit a capsule with 2-4 valves; seeds comose. The Salicaceae is composed of two genera and about 350 species, distributed throughout most of the world. It differs from other catkin -bearing families by its dioecious nature, its bracteate flowers, and its comose seeds. Salix / 7 The absence of a perianth is interpreted by most botanists as a reduction from some ancestor having a perianth. Many species of both Salix and Populus are grown as ornamentals . KEY TO THE GENERA OF Salicaceae IN ILLINOIS 1. Leaves twice as long as broad or longer; bud scale 1; catkins not drooping _ _ _ _ __ _ _ _ _ __ __ _ ____ __ _ _ __ ___ _ __ ___ _ _ __ _ __ __ _ _ _ _ ___ __ _ _ _ 1. Salix 1. Leaves never twice as long as broad; bud scales several; catkins drooping ____________________________________________________ 2. Populus 1. Salix L. - Willow Dioecious trees or shrubs; buds with only one scale; leaves alternate , rarely subopposite; flowers unisexual, without a perianth; staminate flowers in erect or spreading aments, each flower subtended by one bract and 1-2 glands, with (1-) 2 (-10) stamens with free or basally connate filaments; pistillate flowers in erect or spreading aments, each flower subtended by a bract and 1-2 glands, with one pistil, the ovary superior, the 2 stigmas entire or 2-cleft; capsule 2-valved, with several cornose seeds. Salix differs from Populus by its elongated leaves and its buds with a single scale. In addition, all Illinois species of Salix have erect or spreading catkins, as opposed to the pendulous catkins of Populus . There are about 300 different species of Salix, primarily in the north temperate and arctic regions of the world. In addition, a substantial number of hybrids has been reported. Several species of Salix are common in cultivation. Included among these are the weeping willow (S. babylonica L.), the pussy willow (S. discolor Muhl.), the crooked willow (S. matsudana Koidz. var. tortuosa Hort.), the white willow (S. alba L.), the brittle willow (S. fragilis L.), the osier willow (S. viminalis L.), the purple osier (S. purpurea L.), and Thurlow's weeping willow (S. elegantissima Koch). Several botanists have given considerable attention to the taxonomy of the genus. Foremost among those have been the treatments by Schneider (1921) and Raup (1943). In addition, Carlton R. Ball's studies on Salix have been highly respected in the United States. Twenty-three species and two named hybrids are recognized in the Illinois flora. These fall into fifteen sections according to the treatment by Schneider (1921). Following is a summary of these sections and a list of the Illinois species in each. 8/ WILLOWS TO MUSTARDS§ Nigrae. Bracts falling away before capsule matures; stamens 3-6; flowers in whorls; pistillate flower with one gland; leaves green beneath. Salix nigra.§ Bonplandianae. Bracts falling away before capsule matures; stamens 3-12; flowers in whorls; pistillate flower with one gland; leaves whitened beneath; stipules persistent; capsules...