Gametophyte Morphology and Development of Three Species of Cyrtogonellum Ching (Dryopteridaceae).

Gametophyte morphology and development of three species of Cyrtogonellum Ching (Dryopteridaceae) were described with the aim to increase our knowledge on the gametophytic stage of this fern genus especially the occurrence of sexual structures. Spore germination followed the Vittaria-type development, whereas prothallus growth followed the Aspidium-type development. Unicellular glandular hairs were located on both margins and surface of the prothalli. The heart-shaped prothalli of C. caducum showed irregularly lobed margins with multicellular filamentous to wing-like extensions. One to several agamously formed embryos were found on a single mature gametophyte of C. inaequale but only one of these developed into a mature sporophyte. Young sporophytes possessed scales with one to several glandular cells. Antheridia were found in all three species, but archegonia were observed only on mature prothalli of C. fraxinellum, which were always located near the midrib of the cordate-thalloid prothallus. The rarity of archegonia and lack of evidence for the functionality of archegonia in these species raised questions about sexual reproduction in Cyrtogonellum. [ABSTRACT FROM AUTHOR]