Systematics/Phytogeography / Taxonomie/ Section
Welsh, Mark , Stefanovic, Sasa , Costea, Mihai .
Pollen evolution and its systematic significance in Cuscuta (dodders, Convolvulaceae).
Pollen morphology of 150 species of Cuscuta was investigated in relation to a phylogeny obtained from a combined analysis of rbcL and 26S rDNA gene sequences. The size of the pollen grains, their shape, number of colpi, and exine characteristics were examined with the SEM. Considering that Cuscuta is one of the most diverse genera of parasitic plants, the pollen of dodders is surprisingly uniform. The largest infrageneric unit, Grammica, exhibits more variation than all the three other groups—Monogynella, Cuscuta, Pachystigma—combined. A reticulated pollen, defined by irregularly shaped lumina, 1500–3500 nm, is characteristic to Monogynella, and interestingly, several species of a South American clade of Grammica (Clade O). ‘Tectum imperforatum’ and ‘perforatum’ are largely shared by Cuscuta, Pachystigma and Grammica. In the former, tectum covers the small puncta (50–250 nm in diameter) and pollen grains appear smooth at magnifications lower than 4000x; in the latter puncta are visible (200–500 nm in diameter). Although the sister group of Cuscuta in Convolvulaceae is unknown, given the prevalence of tectate pollen in the genus and the family, and the fact that the reticulate condition is unknown in other genera, the latter is likely to be a synapomorphy. A similar pattern can be observed in the number of colpi, which is commonly three in most Cuscuta species and numerous Convolvulaceae, but 5 to 8 in some species of Monogynella and the clade O of Grammica. Additionally, in Grammica a ‘microreticulate’ pollen with more or less regular perforations, 500–1500 nm in diameter has evolved at least in five different clades. An intergradation between these morphological ‘types’ may occur in the subgenera Cuscuta, Pachystigma and Grammica indicating that although useful for taxonomic purpose, these tipologies represent merely ranges of variation within an evolutionary continuum.
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Digital Atlas of Cuscuta
1 - Wilfrid Laurier University, Botany, 75 University Avenue W, Waterloo, Ontario, N2L 3C5, Canada
2 - University of Toronto at Mississauga, Biology, 3359 Mississauga Rd N, Mississauga, Ontario, L5L1C6, Canada
3 - Wilfrid Laurier University, Biology, 75 University Ave N, Waterloo, Ontario, N2L3C5, Canada
Presentation Type: Poster:Posters for Sections
Location: Ball Room & Party Room/SUB
Date: Monday, July 28th, 2008
Time: 12:30 PM