Styrax in cultivation: Evaluation of an underrepresented ornamental genus

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University of Delaware
Styrax (Styracaceae) is a genus consisting of approximately 130 species of woody, dicotyledonous, often resinous trees and shrubs with a wide distribution spanning temperate and tropical regions of the Americas, the Mediterranean, and East and Southeast Asia. The taxonomy of the group is historically confused, with numerous published names, arguably with little justification. Recent revisions of the North American distribution and imbricate group of the East Asian component have largely alleviated this problem, though the valvate group of the latter as well as the Neotropical species of the genus are yet to be treated. Several species, primarily of East Asian origin, have been grown and appreciated as ornamentals but make up only a minute fraction of those known and described in the literature. Anatomical variation between species includes ploidy level as well as differences in the shape of the petiole vasculature and several characteristics associated with both the axial and radial systems of the secondary xylem. Surveys of public garden collections reveal that Styrax japonicus, Styrax obassia, Styrax americanus, and Styrax grandifolius are by far the most commonly cultivated and accessioned species. Several other ornamental species such as Styrax officinalis, Styrax hemsleyanus, and Styrax wilsonii are also somewhat represented though rare, and certainly worthy of greater use. The ornamental potential of the group is vast and largely underutilized and should be seriously considered for further representation in botanical garden collections. The exact chromosome number of Styrax japonicus could not be determined due to the small size of the chromosomes, but results strongly support a diploid in addition to pentaploid and hexaploid levels to the species. Examination of petiole anatomy revealed significant variability in the shape of the vasculature and number of accompanying bundles within plants of the same species, suggesting the petiole is of limited use as an identification characteristic. Examination of transverse sections of wood anatomy of several species of Styrax sect. Styrax ser. Cyrta suggested possible differences between species not found in the literature, though all results should be taken as tentative due to the limited sample size and lack of analysis of longitudinal sections.