TYPES OF CAMBIAL ACTIVITY AND WOOD ANATOMY OF STYLIDIUM (STYLIDIACEAE)

Three types of cambial activity, two hitherto unreported, are described for Stylidium. The four species of sect. Rhynchangium of subgenus Nitrangium have woody cylinders in upright stems. In these a cambium formed beneath the endodermis produces a determinate quantity of fibers, vessel elements, and interxylary phloem strands toward the inside but no derivatives toward the outside; this was correctly reported by Van Tieghem and Morot (1884a) but doubted by subsequent workers. The same species have lignotubers in which a cambium produces contorted xylem (mostly vessels) to the inside, phellem toward the outside. In S. glandulosum and S. laricifolium a cambium formed beneath the endodermis produces an indeterminate quantity of xylem (fibers and vessel elements) and interxylary phloem toward the inside, nothing toward the outside. The xylem is rayless and lacks axial xylem parenchyma. These three modes of cambial activity represent innovations within Stylidiaceae. The family has a wholly herbaceous ancestry if one can judge from the total lack of cambial activity in vascular bundles. THE FAMILY STYLIDIACEAE appears to have very little secondary growth. Indeed, the family can be said to have a monocotyledonous plan of organization to a remarkable degree. Vascular bundles are devoid of any cambial activity; in most species vascular bundles are not arranged in a single cylinder but are scattered within a zone around the pith; roots are adventitious (Van Tieghem and Morot, 1884a; Mildbraed, 1907). Stylidium glandulosum Salisb. and S. laricifolium L. C. Rich. do have secondary growth evident upon superficial examination. The type of cambial activity which produces wood in these species has not been hitherto analyzed, nor has the wood of this pair of species been described. However, material sufficient for study of both is now at hand. In addition, the section Rhynchangium Benth. of Stylidium subgenus Nitrangium Endl. offers some unusual problems. This section consists of S. adnatum R. Br., S.falcatum R. Br., S. fasciculatum R. Br., and S. rhynchocarpum Sond. These closely related species are perennials which branch from a lignotuberous base appearing to be a fusion of stems or occasionally a knotlike thickening (Fig. 9). Research has been done on the upright stems of S. falcatum, which was widely cultivated in Europe in the 19th century (Van Tieghem and Morot, 1884a). These workers reported a form of cambial activity in the upright stems (Van Tieghem and Morot, 1883, 1 Received for publication 21 March 1980; revision accepted 18 March 1981. 1884a, 1884b). Doubt was cast on this interpretation by Burns (1900), and the issue has not been resolved. The lignotubers of the Rhynchangium species have not been investigated until now, however. The anatomy of these structures proves to be yet another facet in the story of cambial activity of Stylidiaceae. Misunderstanding of types of secondary growth in Stylidium has resulted in omission of the family from lists of groups which possess interxylary phloem in wood. More importantly, the types of cambial activity in the family pose phylogenetic problems of considerable