Gametophytes from these plants are not well known, but some plants that
were probably gametophytes were upright, branched structures resembling a
sporophyte. Structures resembling archegonia and antheridia were borne in
cup-like structures on the tops of the stems, some of which were lobed (Fig. 4). It
is likely that rain splashes dispersed the sperm, perhaps often to neighboring
archegonia effecting self-fertilization. In many ways the fertile cup-shaped
structures must have resembled the ‘inflorescences’ of some mosses (Topic P4)
in habit and function. It also suggests that in some, at least, of these early plants,
the alternation of generations may have been isomorphic, i.e. between a sporo-
phyte and a gametophyte that resembled each other, as in some algae. If other
gametophytes were small and growing on the soil surface, as in living relatives
of these plants, it is likely that preservation will be poor. The early evolution of
gametophytes remains unknown.276 Section Q – Spore-bearing vascular plants
SporangiaFig. 3. Psilophyton(Trimerophytopsida), showing lateral clumps of sporangia.Fig. 4. Tip of stem of a gametophyte, Lyonophyton,showing probable antheridia and
archegonia. (Redrawn from Stewart and Rothwell (1993). Paleobotany and the Evolution of
Plants,2nd Edn. Cambridge University Press.)AntheridiaArchegonia1 mm