SELF, SHERRY L.*, C. HEATHER FORD, AND BARBARA CRANDALL-STOTLER. Department of Plant Biology, Southern Illinois University, Carbondale, IL 62901-6509. - Shoot/sporophyte associations in the Fossombroniineae.
The Fossombroniineae comprise four genera of simple thalloid
liverworts, namely, Fossombronia, Austrofossombronia,
Petalophyllum and Sewardiella. A character presumed to
unite the taxa of the suborder is the enclosure of the sporophyte in a
calyptra which is in turn surrounded by a leaf-like pseudoperianth.
Although many authors accept this interpretation of the
shoot/sporophyte association, the developmental studies of Chalaud
(1928. Rev. Gen. Bot. 41: 1-343, 8 Pl.) suggest that the structures
produced in Fossombronia are not homologous to the
pseudoperianths of the other taxa. Using serial paraffin sectioning
and SEM techniques, we have investigated pseudoperianth formation and
growth in several species of Fossombronia and
Petalophyllum. In Petalophyllum a true pseudoperianth,
formed from extensions of the lamellae, surrounds the cluster of
unfertilized archegonia; following ferilization, the pseudoperianth
expands and a shoot calyptra develops around the sporophyte. In
contrast, Fossombronia first forms a perigynial mass beneath
the fertilized egg. One or two leaf-like scales are subsequently
produced at the apex of this perigynial mass at its point of juncture
with the calyptra. This developmental sequence agrees with Chalaud's
interpretation and verifies that the leaf-like structure that encloses
the sporophyte in Fossombronia is not a pseudoperianth.
Key words: development, Fossombronia, perigynium, Petalophyllum, pseudoperianth