Master of Science (MSc)
Faculty of Science
Dr. Mihai Costea
Cuscuta (dodder, Convolvulaceae) is a genus of about 200 species of obligate stem parasites of cosmopolitan distribution. Infrastaminal scales (IFS) are staminode-like formations that surround the ovary in the flowers of dodders. Their morphological diversity has historically provided some of the most useful taxonomic diagnostic characters at the species-level, however, their function had not been determined. I performed a comparative study of the IFS in 147 taxa using light, scanning and transmission electron microscopy, and results were analyzed in relation to a Cuscuta phylogeny obtained from a combined analysis of rbcL and 26S rDNA gene sequences. To test the hypothesis that the role of IFS is related to sexual reproduction, I analyzed the correlations between IFS characters and the production of pollen/ovules in the flower and the number of stomata found in the nectary at the base of the ovary. With a few exceptions, the IFS exhibit numerous fimbriae that contain laticifer cells secreting a complex resin-glycoside latex. In subgenus Monogynella, fimbriae are similar to uniseriate glandular hairs. In the derived subgenera Grammica and Cuscuta, the fimbriae have laticifers that are enclosed and protected by an epidermis which leaves the distal ends of the laticifers exposed. The slightest mechanical contact with the exposed part of the laticifer cells (for example by an insect) causes them to burst open and release the latex. It was found that the relationship between IFS size with both pollen/ovule ratios and nectary stomata number is weak at the level of the entire genus. Subgeneric partitions, however, revealed a strong correlation in subgenus Monogynella. These results suggest that scales in Cuscuta evolved from nectar holding in the first diverged subgenus Monogynella, to ovary protection against herbivorous insects in the derived subgenera Cuscuta and Grammica. This study further details the morphological diversity of the IFS in Cuscuta, confirming their significance for the species-level systematics.
Riviere, Stephanie, "Morphology, Structure, Function and Evolution of Infrastaminal Scales in Cuscuta (Convolvulaceae)" (2013). Theses and Dissertations (Comprehensive). 1612.