Jamesonia is a genus of Neotropical ferns that belongs to the
subfamily
Taenitidoideae, Pteridaceae. Approximately 20 species have been
recognized
in the genus (Tryon, 1962). Jamesonia occurs from Mexico to
central Bolivia and Brazil, in páramos or cool wet
highlands,
ranging from 1500 to 5000 m.
Páramos are characterized by having strong winds, high levels of insolation, high moisture in the soil, the air in form of clouds or fog, and cool temperatures ranging from 12 °C to -2 °C. There are diurnal fluctuations in temperatures with freezing during the night.
The most outstanding morphological features of the species in this genus are: 1) indeterminate growth, 2) xeromorphic and coriaceous pinnae, 3) pubescence, and 4) extremely reduced pinnae. These structural variations may represent evolutionary trends that were favored by the extreme environmental factors prevailing in páramo ecosystems.
Eriosorus appears to be the closest relative of
Jamesonia
(Tryon and Tryon, 1982), and also exhibits a Neotropical
distribution.
Eriosorus is mainly found in cool and moist highlands such as cloud
forests and sub-páramos, and approximately 25 species have been
recognized (Tryon, 1970). Eriosorus is primarily restricted
to the Andes, however its geographical distribution extends from Mexico
and the West Indies south to Bolivia, Brazil and Uruguay; also on Tristan
da Cunha and Gough Island.
More than half of the taxa occur above 2200 m. and only three are limited to occur below 1800m. Andean fossil records indicate that spores of Eriosorus first appeared during the Oligocene.
This genus exhibits a wide variety of morphologies, which range from bipinnate to pinnate, representing the transitional changes that are hypothesized to be resulted in the morphology of Jamesonia. Their ecological diversity is quite remarkable since different species are found from cloud forest to páramo ecosystems.