GEMMIFEROUS FERN GAMETOPHYTES—VITTARIACEAE

Approximately 10 % of all fern species reproduce vegetatively in the gametophytic stage by means of gemmae. Gametophyte morphologies in these species depart radically from the commonly figured heart-shaped type and expand considerably the opportunities for physiological and morphological studies utilizing fern gametophytes. Original observations on four species of vittarioid ferns are presented and compared with earlier observations on gametophytes of this family. Vittarioid gametophytes grow from a discontinuous marginal meristem which results in a much branched thallus of indeterminant growth. Aerial branches of the gametophytes terminate in gemma production, which proceeds by a regular and predictable sequence of events. The sequence may differ considerably among species but is remarkably constant within species. Archegonia are produced on short ventral branches, and antheridia are produced primarily on germinating gemmae. Ananthacorus angustifolius is the only known member of the Vittariaceae which does not produce gemmae and is considered to represent the primitive condition. In this species antheridia are scattered over the thallus, suggesting that a change in the mode of control of antheridium production may have evolved in the family along with gemma production.