Ökologisch‐physiologische Untersuchungen an den Podostemonaceen des Caroni

Podostemaceae Depend on Sticky Biofilms with Respect to Attachment to Rocks in Waterfalls

“…The existence of nitrogen-fixing heterocysts within the biofilm is certainly a most interesting aspect regarding the nutrient cycle of an ecosystem on "naked" rocks of oligotrophic rivers. Oligotrophy, i.e., a low level of electrolytes and nutrients, is characteristic of rivers inhabited by Podostemaceae (Venezuela: Gessner and Hammer 1962;Grubert 1974;Mexico: Quiraz et al 1997). Cyanobacteria in biofilms might possibly contribute to the nitrogen supply of the habitat.…”

“…48 genera, 270 species) inhabit rocks in the turbulence of waterfalls and cascades. The foam of the waterfalls ensures a sufficient supply of gaseous carbon dioxide dissolved in the water that Podostemaceae are only able to use, of course, for assimilation (Gessner 1959;Pannier 1960;Gessner and Hammer 1962). Podostemaceae are, therefore, bound to this strange habitat where they have to withstand enormous tensile stress that results from the running water (Grubert 1974).…”

Principles of Dispersal in Higher Plants

“…Willis (see Ridley) reports for Ceylon that the seeds of Lawia become mucilaginous when wetted and may stick to the feet of birds walking ovcr the rocks. In Venezuelan species of Rhyncholaxis and Mourera, Gessner and Hammer (1962) saw very fast mucilage formation; they think that this serves the purpose of anchoring seeds to rocks, a process which in this case is demonstrably effective even in running water. An objection to direct water dispersal is that at this period the water level is said to be far below the level where the plants are ultimately found attached, which is the highest level ever reached by the water.…”

Physioecological Problems in the Tropics

“…Annual rings have been found in species of extreme habitats such as temporary flooded "gallery forests" of tropical rivers (Gessner, 1968), the high "paramos" exposed to periodic temperature changes (Trautner-Jaeger, 1962), and the tidal zone of mangrove forest (Gill, 1971). Annual rings have been found in species of extreme habitats such as temporary flooded "gallery forests" of tropical rivers (Gessner, 1968), the high "paramos" exposed to periodic temperature changes (Trautner-Jaeger, 1962), and the tidal zone of mangrove forest (Gill, 1971).…”