The smallest type of Gunnera, represented by the single elusive species Gunnera herteri first described in 1933 by Mattfield. This is probably the most "primitive" form of Gunnera, as all recent phylogenetic studies agree that it is the first branch in the evolutionary tree of Gunnera. It is probably dervied from the Gondwanaland ancestors of Cretaceous era Gunnera and today it occurs in eastern South America, including Southeast Brazil and Uruguay.

 Unlike other Gunnera subgenera Ostenigunnera lacks the cataphylls the protect its growing apex, and it lacks the hairs (unicellular trichomes) that are common on the leaves of all other Gunnera.