Floral structure and development in Rafflesiaceae with emphasis on their exceptional gynoecia

Author(s)
Lachezar A. Nikolov, Yannick Städler, Sugumaran Manickam, Jürg Schönenberger, Peter K. Endress, Elena M. Kramer, Charles C. Davis
Abstract

Premise of the study: The holoparasitic plant family Rafflesiaceae include the world's largest flowers. Despite their iconic status, relatively little is known about the morphology and development of their flowers. A recent study clarified the organization of the outer (sterile) floral organs, surprisingly revealing that their distinctive floral chambers arose via different developmental pathways in the two major genera of the family. Here, we expand that research to investigate the structure and development of the reproductive organs of Rafflesiaceae. Methods: Serial sectioning, scanning electron microscopy, and x-ray tomography of floral buds were employed to reconstruct the structure and development of all three Rafflesiaceae genera. Key results: Unlike most angiosperms, which form their shoot apex from the primary morphological surface, the shoot apex of Rafflesiaceae instead forms secondarily via internal cell separation (schizogeny) along the distal boundary of the host-parasite interface. Similarly, the radially directed ovarial clefts of the gynoecium forms via schizogeny within solid tissue, and no carpels are initiated from the floral apex. Conclusions: The development of the shoot apex and gynoecium of Rafflesiaceae are highly unusual. Although secondary formation of the morphological surface from the shoot apex has been documented in other plant groups, secondary derivation of the inner gynoecium surface is otherwise unknown. Both features are likely synapomorphies of Rafflesiaceae. The secondary derivation of the shoot apex may protect the developing floral shoot as it emerges from within dense host tissue. The secondary formation of the ovarial clefts may generate the extensive placental area necessary to produce hundreds of thousands of ovules.

Organisation(s)
Department of Botany and Biodiversity Research
External organisation(s)
Harvard University, Universität Zürich (UZH), University of Malaya
Journal
American Journal of Botany: the journal for all plant biologists
Volume
101
Pages
225-243
No. of pages
19
ISSN
0002-9122
DOI
https://doi.org/10.3732/ajb.1400009
Publication date
02-2014
Peer reviewed
Yes
Austrian Fields of Science 2012
106042 Systematic botany, 106008 Botany, 106012 Evolutionary research
Keywords
ASJC Scopus subject areas
Plant Science, Ecology, Evolution, Behavior and Systematics, Genetics
Portal url
https://ucris.univie.ac.at/portal/en/publications/floral-structure-and-development-in-rafflesiaceae-with-emphasis-on-their-exceptional-gynoecia(16197f47-af9d-46fc-ab47-c9e9cf116a4b).html