Gametophytes and Juvenile Leaves of Drynarioid Ferns

Abstract

Spores of the six genera (10 spp.) of the drynarioid ferns (Polypodiaceae) studied are monolete, with the exine either granulose, areolate, spinulose, or verrucate. On germination an elongated germ filament is produced; its anterior cells divide longitudinally to form an ameristic prothallial plate. Later an obconical apical meristematic cell is defferentiated. The germ filament of Merinthosorus ends in a hair and the penultimate cells form the prothallial plate; in this a meristematic cell is differentiated laterally. The prothalli develop a cordate apex in which a multicellular meristem replaces the meristematic cell within 4-6 weeks after spore germination. A prothallus attains maturity in about 3 months and at this stage is cordate, usually with a light midrib and broad unruffled wings. The walls of the wing cells in most species show collenchyma-like thickenings. Unicellular papillate hairs are produced on the margin and lower surface of the prothallus, starting with the spatulate or cordate stage of development. In addition, club-shaped hairs, two to four cells long, occur on the mature prothallus of all genera except Drynaria. In Aglaomorpha and Photinopteris unbranched club-shaped hairs are borne marginally also. Sex organs are of the type common in advanced ferns. Antheridia are small and often produce only 4-12 sperms. The first leaf is simple with a medianly placed vascular bundle and bears branched hairs. A midrib with pinnate lateral veins is found in the third to eighth leaves and a reticulate venation pattern occurs in leaves produced by plants over 5 months old. The leaf lamina is simple and lanceolate until the plants are over 3 years old.