Images and an introduction to the plant family Gunneraceae
For further information on Gunnera, try some of the sources below.
On the symbiosis with cyanobacteria, see
On Anatomy, see the excellent studies by Hazel Wilkinson:
An overview of morphology but detailed
The most active researcher on Gunnera at present is Dr. Livia Wanntrop at Stockholm University, who has published a series of studies on systematics, evoltuion and biogeography of Gunnera based on cladistic analysis of some genetic loci. Her publications are listed here. There are some differences in the hypothesized evolutionary relationships resulting from these studies and those of Fuller and Hickey (above), who contend that living Saxifragaceae provide a better morphological (and ecological) model for the Cretaceous ancestors of Gunnera (and perhaps the specialized Myrothamnus as well; for a detailed description of one of these species see this paper by Moore et al. 2007).
In recent years authorities (starting with Takhtajan 1997) have elevated Gunnera into its own order Gunnerales, which is also thought to include the acquatic family Myrothamnaceae on the basis of recent gene-based cladistic macro-phylogenies (see, e.g. the Angiopserm Phylogeny Group website). This placement was taken as a baseline assumption in the within Gunnera studies of Wanntorp and colleagues. Fuller and Hickey would contend that this does not best explain the morphological evolution and historical biogeography of Gunnera and the suggested placement with Myrothamnus could be an artefact of the cladistic methodology such as "long branch attraction".
Clearly further research is warranted!
On the fossil record, especially fossil pollen: