Ranessa L. Cooper
Project Topics / Abstracts:
"Comparative pollen morphology and ultrastructure of the Callitrichaeae"
The Callitricaeae are an aquatic family of dicots that
include the single, geographically cosmopolitan genus
Callitriche. Callitriche contains 40-50 terrestrial,
amphibious, and obligately submersed species, and it is the
only known genus in the plant kingdom with co-occurring
aerial and hydrophilous pollination syndromes. Pollen
morphology and ultrastructure were described for 13
Callitriche species using scanning electron and transmission
electron microscopy. Respresentative taxa of each growth
form were examined: these included three terrestrial species
(C. deflexa, C. peploides, and C. nuttalii), nine amphibious
species (C. brutia, C. cophocarpa, C. cophocarpa-stagnalis
hybrid, C. cribrosa, C. hamulata, C. hereophylla var.
heterophylla, C. lusitanica, C. marinata, and C. trochlearis),
and one obligately submersed speices (C. truncata). Of the
amphibious taxa, C. heterophylla var. heterophylla and
C. trochlearis had internal geitonogamy a type of internal
self-fertilization. Pollen from all taxa was spheroidal,
small intectate, and lacked well-defined apertures. Taxa
primarily differed with respect to exine thickness, surface
ornamentation, and the presence or absence of aperture-like
regions. The pollen of terrestrial species, as well as that
of C. marginata, has well-developed exines with thick
sculptured and basal layers. In general, amphibious taxa
produced pollen with distinct, but thinner, exines than that
of terrestrial taxa. Pollen of the amphibious taxa with
internal geitonogamy, whereas the overall exine was reduced
in C. hamulata and absent in C. brutia and C. lusitanica.
Pollen of the obligately submersed C. truncata also lacked
an exine. These palynological data were correlated with
growth habits and related pollination biologies, as well as
with phylogenetic interpretations of Callitrichaeae. Exine
reduction or loss has evolved at least twice in the family,
and it is associated with aneuploid reduction in chromosome
number.
"Comparative pollen morphology of co-occuring light-flowered and dark-flowered Viola pedata (birdfoot violet)"
Viola pedata (Violaceae), or birdfoot violet, is a species
native to Missouri. This species is unusual in that it
produces both light (LT) and dark (DK) flower morphs. The
five petals of the LT morph are lilac-colored, whereas in
the DK morph the two upper petals are dark violet and the
three lower petals are lilac. The source of variation and
the biological significance of the co-occurring flower
morphs are unclear; however, recent ecological work has
shown a significant correlation between morph proportions in
populations and the relative numbers of ovules of the two
types. In the present study, pollen morphology form the LT
and DK morphs of Viola pedata was comparatively examined
using scanning electron microscopy to ascertain if the
floral variation also exists at the palynological level.
Pollen grains from the two forms were compared with regard
to the following characters: shape, size, surface sculpture,
aperture type, aperture size, and aperture ornamentation. In
addition to perhaps providing insight into the polymorphic
nature of Viola pedata, this study will contribute to the
understanding of pollen morpholy in the genus Viola overall.
Very few investigations have focused on Viola pollen, and
none of these have been carried out at the electron
microscopical level.
Publications:
2000 American Journal of Botany 87: 161-175.
Article |
Abstract
2001 Plant Systematics and Evolution 228: 81-87. Abstract
Presentations:
1995
National Ronald E. McNair Student Research Conference
(Delavan, WI)
1995 California McNair Scholars Symposium
(Berekley, CA)
1995 Ronald E. McNair Undergraduate
Research Symposium (Kirksville, MO)
1995 Tri-Beta Biological Honor Society
Regional meeting (Steelville, MO)
1996 Truman Undergraduate Research
Symposium (Kirksville, MO)
1996 Botanical Society of America
(Seattle, WA)
1996 National Conference on Undergraduate
Research (Asheville, NC)
1996 Sigma Xi Student Research Symposium
(Kirksville, MO)
1996 Truman Undergraduate Research
Symposium (Kirksville, MO)
1997 National Conference on Undergraduate
Research (Austin, TX)
1997 Truman Undergraduate Research
Symposium (Kirksville, MO)
1997 Tri-Beta Biological Honor Society
Regional Meeting (Steelville, MO)
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