DEWITT, K.G.* and T.J. AYERS. Department of Biological Sciences, P.O. Box 5640, Northern Arizona University, Flagstaff, AZ 86011-5640. - Leaf Anatomy of Lysipomia (Campanulaceae): Response to Harsh Environmental Conditions in the High Andes.
The genus Lysipomia Kunth comprises approximately 40
species restricted to the paramo and wet puna of the northern and
central Andes from 3000 to 5000 meters in elevation. Andean paramo and
puna are areas above tree-line that superficially resemble alpine
tundra, but are unique because of the extreme temperature
fluctuations. This habitat is also characterized by high winds, large
amounts of precipitation, and increased UV light levels. Due to these
environmental extremes, Lysipomia has evolved specific
morphological features such as short stature, thick stems, and
persistent leaf bases. Using standard anatomical techniques, we
investigated leaf anatomy of Lysipomia in order to discover
whether specific anatomical features are synapomorphies or whether
they have evolved independently many times in response to harsh
environmental conditions. To test for homology vs. homoplasy
anatomical features were mapped onto a cladogram that was derived from
morphological and molecular data sets. Characters were compared among
the species such as stomatal placement, presence of trichomes,
thickness of epidermal layers, and variation of the pallisade
parenchyma and spongy mesophyll throughout the leaf. The leaves of
some species showed unique features that have not been reported
elsewhere in the family Campanulaceae. The only species that lacked
stomata and exhibited a majority of aerenchyma, L. aquatica, is
found in submerged aquatic habitats. Lignified trichomes in L.
lehmannii and L. aretiodes have independently evolved
possibly in response to the high winds associated with the barren
ridges they inhabit. Stalked stomata and highly thickened epidermal
layers are found only in four species found in southern Ecuador and
can be used as a synapomorphy for the clade. The anatomical study of
Lysipomia illustrates how leaves in a tropical alpine plant can
be modified in response to certain environmental conditions but not
all of the novel adaptations are useful in phylogenetic
analyses.
Key words: Andes, Campanulaceae, harsh environments, leaf anatomy