Observations on the gametophytes of Grammitis billardieri Willd. and Ctenopteris heterophylla (Labill.) Tindale (Grammitidaceae)

Abstract

An account is given of the spores, germination, and vegetative features of the prothalli of Grammitis billardieri and Ctenopteris heterophylla, and of the reproductive organs of G. billardieri.

The characteristic germination is unlike that found in other ferns. The trilete green spore frequently divides in the unruptured sporangium and the first division produces two equal prothallial cells. Growth is extremely slow, the filament long and often branched, and the rhizoids which appear late may branch. The first longitudinal division occurs in a cell back from the apex, and the gametophyte at maturity is elongated and ribbon-like, with or without a slightly indented apex, brown marginal rhizoids, and discontinuous axial cushions two to three cells thick. The thallus, which is extremely slow in reaching maturity, is dark green, and the walls perpendicular to the surface are pitted. Regeneration is common.

The most distinctive feature of the gametophyte of G. billardieri is the development of characteristic spine-like hairs unlike those found on fern prothalli of other families. These hairs are marginal in the anterior region and develop from wedge-shaped initial cells. They differ in form and origin from those found in members of the Polypodiaceae.

The antheridia appear at an unusual stage in development, occurring after some of the archegonia have been produced and forming with them on the cushions. The archegonia have longer necks and the antheridia are slightly more complex than those found in members of the Polypodiaceae which have been investigated.

It is considered that the separation of the family Grammitidaceae from the Polypodiaceae on sporophytic characters is supported by the gametophytic generation of the two Victorian grammitid ferns G. billardieri and C. heterophylla.