Gametophyte morphology and ultrastructure of the extremely deep shade fern, Trichomanes speciosum

The extent to which macro- and micromorphological features might contribute to tolerance of extremely deep shade by Trichomanes speciosum, a member of the filmy ferns (Hymenophyllaceae), is reported here. Confocal laser scanning, transmission and scanning electron microscopy were used to study the ultrastructure of gametophytes and sporophyte leaves. Gametophyte filament cells contain numerous small, spherical or ovoid chlor oplasts, whereas sporophyte leaf cells have fewer, slightly larger, disc-sh aped chloroplasts. The chloroplast grana of gametophytic cells have fewer t hylakoids than sporophyte cells, although grana are not numerous in either. Gametophyte filament cell walls resemble those of sporophyte leaf cells, w ith two or more layers of electron-opaque material and covered in a thin cu ticle. Gemma cell wall ultrastructure does not differ from that of gametoph yte filament cells; rhizoid cell walls are thick and several-layered. Neither gametophyte filaments nor sporophyte leaves have chloroplasts of th e extreme forms reported for deep shade fern or angiosperm leaves. The succ ess of the fern is attributed to a low metabolic rate and inability of othe r species to cope with extreme low light. (C) New Phytologist (2001) 151: 2 43-255.