COMPARATIVE STUDIES OF THE NODAL AND VASCULAR ANATOMY IN THE NEOTROPICAL CYATHEACEAE. I. METAXYA AND LOPHOSORIA

Comparative studies of the nodal and vascular anatomy in the monotypic genera Metaxya and Lophosoria are discussed as they relate to the taxonomy and phylogeny of the Cyatheaceae. Both genera are distinctive and primitive with respect to habit, stem and petiole indument, stelar pattern, and nodal anatomy. Metaxya possesses a prostrate, dorsiventral rhizome, whereas a short, upright radial stem occurs in Lophosoria. Trichomes occur on the stems and leaf petioles of these genera. Both Metaxya and Lophosoria have a spiral phyllotaxy, and adventitious buds occur on the petiole bases. The stelar pattern is basically a siphonostele, although frequently a dictyostele is found in Lophosoria. Accessory bundles are lacking in both genera. A characteristic petiole pattern is found in these genera, with an increase in complexity from an undivided strand in Metaxya to the three-parted petiole pattern in Lophosoria. Data from nodal and vascular anatomy indicate that these taxa are distinct from the other genera in the Cyatheaceae and belong in an independent position at the base of the Cyatheoid line, although in some respects an affinity to members of the Dicksoniaceae is indicated. THE CLASSIFICATION of Metaxya and Lophosoria has undergone several revisions. Early taxonomists placed these genera, together with the Dicksonioid group, in the single family Cyatheaceae (Mettenius, 1856; Diels, 1902; Christensen, 1906; Maxon, 1911). Bower (1926) later stressed the importance of soral position and erected the family Proto-Cyatheaceae to include these primitive tree-fern genera. Later workers included these genera in the family Cyatheaceae (Christensen, 1938; Copeland, 1947), but excluded the Dicksonioid genera. Based upon morphological, developmental, and anatomical characters, Holttum and Sen (1961) again incorporated Metaxya and Lophosoria and the Dicksonioid genera into a single family Cyatheaceae. Recently Tryon (1970) has revised the classification of the family Cyatheaceae, excluding members of the Dicksoniaceae. Tyron's classification recognizes Metaxya and Lophosoria as distinctive genera in the Cyatheaceae and places them in an independent position at the base of his phyletic chart. His treatment includes a discussion of the synonymy of these genera. The present study is part of a broad anatomical 'Received for publication 13 April 1973. Based on a doctoral dissertation submitted to Department of Botany, Duke University, in partial fulfillment of requirements for the Ph.D. degree. Portions of this research were supported by NSF GB-6393 and GB-8678 to R. A. White, Department of Botany, Duke University, and GB-27365 and GB-27494 to the Department of Botany, Duke University. 2 Present address: Dept. of Botany, University of Florida, Gainesville 32601. investigation of the Cyatheaceae (sensu Tryon, 1970) and stems from the need to resolve the differences in proposed systems of classification and to respond to the complete lack of knowledge regarding the anatomy of New World tree ferns. Knowledge of the basic vascular patterns of Metaxya and Lophosoria, when coordinated with the patterns in other tree fern genera, may contribute to the solution of the basic problems of systematics and evolution in the tree ferns. MATERIALS AND METHODS-Plant materials were collected in Costa Rica in the montane and lowland rain forests. Developing shoot tips (5-8 in. in length) of both Metaxya and Lophosoria were collected with a machete from within the dense vegetation of the forest and alongside logging roads (Fig. 1, 2). The plant parts were killed and fixed in formalin-acetic acid-alcohol (FAA). No additional preparation was required prior to sectioning the shoot tips. Because of the rather large diameter (up to 4 in.) of the shoot tips a device known as a "macrotome" was used to serially section the plant materials. A macrotome is a modified meat slicer (Globe, Model 215) that has enabled the author to work with shoot tips up to 6 in. in diam and 1 ft in length and to obtain serial "sections" (slices) from which the nodal patterns of Metaxya and Lophosoria were reconstructed three-dimensionally and comparisons of the vascular anatomy made. The sections are 500-1000 in thickness and are unstained. The natural colors of the sec-