We summarize the current information on gametophytic plants from the L
ower Devonian that are represented by three types based on perminerali
zations in the Rhynie Chert, two of which are antheridial (Lyonophyton
and Kidstonophyton) and one that is archegoniate (Langiophyton). Impr
ession and compression remains attributed to Sciadophyton and Calyculi
phyton also are interpreted as gametophytic, based on their similarity
to the permineralized forms. All are axial structures, with some axes
terminating in cup-shaped gametangiophores on or in which gametangia
occur, and all exhibit preserved cuticles with stomata and conducting
tissue. Similarity in epidermal and conducting cell characters serves
as a basis for postulating sporophyte relationships for the Rhynie Che
rt gametophytes as follows (N-2N): Lyonophyton-Aglaophyton, Kidstonoph
yton-Nothia, and Langiophyton-Horneophyton. Comparison with bryophytes
and tracheophytes shows that these forms exhibit unique combinations
of characters. They are more advanced than bryophytes in some features
but differ in conducting cell type from tracheophytes. Thus they may
represent lineages distinct from either of these groups. Their constru
ction indicates some degree of morphological similarity between haploi
d and diploid thalli in the life cycles of these entities, thus suppor
ting to some extent an alternation of isomorphic generations and the h
omologous theory of sporophyte origin for land plants. Alternatively,
these data may indicate the early establishment of axial gametophytic
structures within the context of an antithetic theory of sporophyte or
igin.