The gametophyte-sporophyte junction in Apotreubia hortonae (Treubiaceae, Hepaticophytina): Structure and systematic implications
Frey, Wolfgang; Hilger, Hartmut H.
The gametophyte-sporophyte junction of Apotreubia hortonae consists of a bulbous foot with an indistinct collar, embedded in the parental gametophyte tissue. Both generations are separated by a placental space filled with collapsed cells of gametophyte origin. The ultrastructural organization of the outermost cell layers of the sporophyte foot and the surrounding parental gametophyte tissue, the placenta, is unique in archegoniate land plants. On the sporophyte side of the placenta there are clusters of 1-2 layered cells with coarse wall ingrowths (transfer cells) alternating with clusters of cells without wall ingrowths. Gametophyte placental cells lack wall ingrowths. The unique structure indicates an isolated position of Treubiopsida within Hepaticophytina (liverworts), but with a Jungermanniopsidalean affinity.