FLOYD, SANDRA K.* AND WILLIAM E. FRIEDMAN. Department of Environmental, Population, and Organismic Biology, Campus Box 334, University of Colorado, Boulder, CO 80309. - Endosperm development in Amborella trichopoda:implications for the origin and early evolution of angiosperm reproductive biology.
The recent unprecedented concurrence of several independent
phylogenetic analyses of basal angiosperm taxa has led to the
identification of the three earliest diverging lineages of extant
flowering plants: Amborella trichopoda, Nymphaeales, and
Illiciales. With a more confident identification of the earliest
angiosperm lineages, we are now in a better position to resolve
character polarity and identify character state transitions during the
earliest radiation of extant flowering plants. Because of its
phylogenetic position as sister to all other angiosperms,
Amborella is critical to assessing angiosperm character
polarity and evolution. However, little is known about the basic
biology of Amborella, which is endemic to New Caledonia, not
widely cultivated, and thus insufficiently studied. In particular,
embryological data are completely lacking. Endosperm is the
sexually-derived embryo-nourishing structure that is unique to the
life cycle of angiosperms. We provide the first report of endosperm
development in Amborella. The endosperm exhibits a bipolar,
cellular developmental pattern that is quite similar to other basal
angiosperm taxa we have investigated, most notably Illicium,
another representative of the three earliest-diverging lineages of
flowering plants. In contrast, endosperm in Amborella is quite
unlike endosperm in Cabomba and other Nymphaeales. The
implications of these findings for understanding the origin and
evolution of this distinctive aspect of the reproductive biology of
flowering plants are discussed.
Key words: Amborella, basal angiosperms, character evolution, development, endosperm, reproductive biology