The Espeletia complex includes over 100
species that belong to the sunflower family (Asteraceae, tribe Heliantheae).
These plants are found only in the high elevations of the northern
Andes mountains of Venezuela, Colombia and Ecuador. The center of
diversity is the Venezuelan Andes, while the eastern cordillera
of Colombia also has a large number of species. The range of the
complex extends from the coastal Caribbean mountains of Venezuela,
north along the Sierra de Perijá to the Sierra Nevada de
Santa Marta of Colombia, and south into northern Ecuador. The southernmost
extent of the range is a disjunct population in an isolated páramo
of central Ecuador known as the Serranía de Llanganates. |
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The genus Espeletia was first described in Plantae
Aequinoctiales in 1809 by Aimé Bonpland and Alexander
von Humboldt. While traveling in the New World they spent many months
exploring the Spanish colony known at the time as the Nuevo Reino
de Granada, which includes modern day Venezuela, Colombia and Ecuador.
During their visit to Colombia in 1801, they met José Celestino
Mutis, director of the Royal Botanical Expedition. Mutis introduced
Humboldt to the páramos above Bogotá and to species
of Espeletia, which he named in honor of Don José
de Ezpeleta, a viceroy of the colony (1789-1797) who had supported
the botanical expedition. Locally, these species are known by the
common Spanish name "frailejon" because the erect stem
and cloak of brown leaves characteristic of some species make them
look like monks ("frailes"). |
The most recognizable growth form in the Espeletia complex
is the giant rosette. It is characterized by having an unbranched
stem, often covered in a thick layer of dead leaves, topped by a
rosette of spirally arranged, wooly leaves. Unlike most plants in
the páramo, which tend to be short grasses, small herbs and
shrubs, the giant rosettes of the Espeletia complex can
grow from 2 to 5 meters tall and may live for well over 100 years.
Many of the morphological and physiological traits of the giant
rosettes are thought to be adaptations to the harsh tropical montane
climate, which is subjected to frequent frosts and high levels of
solar radiation. Dead leaves on the stem provide insulation, and
the spiral arrangement of the leaves protects the delicate meristem.
The dense layer of hairs on the leaves may provide both thermal
insulation and protection against UV radiation. Interestingly, the
giant rosette growth form has evolved independently in plants from
similar habitats around the world, for example, the silverswords
of Hawaii and giant senecios and lobelias of Africa, suggesting
that this growth form is indeed an adaptation to the tropical montane
environment.
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In addition to the giant rosette, the evolutionary radiation of
the Espeletia complex has resulted in an astonishing diversity
of morphological forms, ecological specializations and life history
traits. These species are found from the montane forests at about
2800 meters, to the edge of the glaciers at 4600 meters, and have
adapted to a wide range of environmental conditions, from steep
talus slopes and xeric rock outcrops, to wet marshes and bogs. Growth
forms range from tiny, mat-forming sessile rosettes less than 5
cm tall, to giant rosettes, to branched shrubs and even large trees
over 15 m tall. In addition, there is significant variation in reproductive
characters including inflorescence and capitulum structure, mechanisms
of pollination (both animal and wind) and life history strategy
(both polycarpic and monocarpic). This diversity is remarkable for
a group which is thought to be less than 5 million years old. The
recent origin and morphological and ecological diversity of this
speciose complex makes it a classic example of adaptive radiation
in plants. |
Much of what we now know about the distribution, diversity, evolution
and taxonomy of the Espeletia complex was contributed by
one of the great botanists of the 20th century, José Cuatrecasas.
He not only discovered and described many of its species, but also
provided a wealth of hypotheses on their evolution and biogeography.
After decades of study, Cuatrecasas elevated the genus Espeletia
to a subtribe, the Espeletiinae, and separated the species into
eight segregate genera, including Espeletia, Coespeletia,
Espeletiopsis, Ruilopezia, Libanothamnus,
Tamania, Carramboa and Paramiflos. Recent
molecular studies, however, suggest that these species should not
be considered a separate subtribe, but instead a complex of species
within the subtribe Melampodiinae, and that at least some of these
genera may not be natural (monophyletic) groups. Nevertheless, our
understanding of the evolution of this complex has only just begun
and will require many more years of research, including molecular
and morphological studies, as well as studies of the biogeography,
ecology and ecophysiology of its species. |
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