In the 9 spp. ofPolystichum studied, a uniseriate germ filament is produced on spore germination. The anterior cells of the germ filament develop into a prothallial plate commonly before or sometimes after the terminal cell develops a papillate hair. A meristematic cell is differentiated early during plate formation, commonly in one of the daughter cells of the terminal cell or rarely (when the terminal cell is quiescent and hair-bearing as inP. aculeatum andP. lentum) of the penultimate cell. Young thalli become cordate inc. 8 weeks from spore germination and fully grown inc. 3 months. The mature prothallus is profusely hairy and cordate with a thick midrib and spread-out wings. Hairs are of the capped, unicellular, papillate type; a few club-shaped, unicellular hairs devoid of terminal caps are found in addition on the anterior margin. Sex organs are of the usual leptosporangiate type. The antheridium dehisces by a pore-like opening formed in the cap cell.