THE DEVELOPMENTAL ANATOMY OF METAXYA-ROSTRATA (FILICALES, METAXYACEAE)

The systematically problematic fern Metaxya rostrata, commonly regarde d as an ally of the cyatheoid and dicksonioid tree ferns, is investiga ted, and features of its organography, shoot vascular anatomy and deve lopment, soral initiation and early development, and gametophyte struc ture are described. The rhizome is creeping, dorsiventral, with an unu sual four-seriate phyllotaxis. Typical protoxylem is lacking from the internodes of the solenostele, but are present in the leaf trace and e nd blindly proximally. Tangential cells are found in the phloem of the stem. The early maturing ''protoxylem'' of the stem is scattered, and , apart from some identifiable protoxylem strands, is not clearly asso ciated with the young leaves. Sori rue initiated as groups of large ce lls on the abaxial side of developing leaflets, distant from the margi nal meristem initials, and in close association with a lateral vein. T wo sori may arise by the subdivision of a single large patch of cells. Soral maturation is of the simple type. Gametophytes are cordate to r ibbonlike, with moderately primitive gametangia. Morphologically and s ystematically, Metaxya appears isolated. It shares few significant der ived conditions with the tree ferns, and a separate family Metaxyaceae seems well justified.