Developmental and Structural Section
Friedman, William E. .
Hydatellaceae are water lilies with gymnospermous tendencies.
For over a century, the flowering plant family Hydatellaceae was thought to belong to the Poales, a highly derived monocot order that includes the grasses. New molecular phylogenetic evidence shows that this obscure group of minute aquatic plants is closely related to Nymphaeales, which themselves were recently discovered to be one of the most ancient extant lineages of angiosperms. Female gametophyte development and endosperm ploidy Hydatella inconspicua (recently renamed Trithuria inconspicua) precisely match the unique and potentially plesiomorphic patterns characteristic of most early divergent angiosperm lineages (Nymphaeaceae, Cabombaceae, Austrobaileyaceae, Illiciaceae, Schisandraceae). At maturity, the female gametophyte is four-celled and four-nucleate, with two synergids, an egg cell and a uninucleate central cell; consequently, endosperm in Hydatella is diploid. As with all members of the Nymphaeales, endosperm in Hydatellaceae is minimally developed and perisperm is the major embryo-nourishing tissue within the seed. Remarkably, Hydatella exhibits a maternal seed-provisioning strategy that is unique among flowering plants, but common to all gymnosperms: pre-fertilization allocation of nutrients to the embryo-nourishing tissue. This exceptional case of pre-fertilization maternal provisioning of an ovule/seed in Hydatella may well be an apomorphic feature of Hydatellaceae alone. If so, it is more strong proof that the earliest phases of flowering plant evolution were marked by a significant degree of developmental lability and a tremendous diversification of reproductive features. Alternatively, pre-fertilization maternal resource allocation to ovules/seeds, and specifically to a maternally derived perisperm, in Hydatella could represent a plesiomorphic and transitional condition associated with the origin of flowering plants from gymnospermous ancestors. The prospect that the first angiosperms might have used both a perisperm and an endosperm to nourish the embryo within a seed and that the maternal plant allocated reserves to this perisperm before fertilization, is thoroughly congruent with the data derived from Hydatellaceae and its newfound phylogenetic position.
Log in to add this item to your schedule
1 - University of Colorado, Department of Ecology and Evolutionary Biology, Boulder, CO, 80309, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Tuesday, July 29th, 2008
Time: 11:00 AM