Hydatellaceae are water lilies with gymnospermous tendencies

The flowering plant family Hydatellaceae was recently discovered to be allied to the ancient angiosperm lineage Nymphaeales ( water lilies)(1). Because of its critical phylogenetic position, members of the Hydatellaceae have the potential to provide insights into the origin and early diversification of angiosperms(2). Here I report that Hydatella expresses several rare embryological features that, in combination, are found only in members of the Nymphaeales. At maturity, the female gametophyte is four- celled, four- nucleate and will produce a diploid endosperm, as is characteristic of most early divergent angiosperm lineages(3,4). As with all members of the Nymphaeales, endosperm in Hydatella is minimally developed and perisperm is the major embryo- nourishing tissue within the seed(5,6). Remarkably, Hydatella exhibits a maternal seed-provisioning strategy that is unique among flowering plants, but common to all gymnosperms(7): pre- fertilization allocation of nutrients to the embryo- nourishing tissue. This exceptional case of pre- fertilization maternal provisioning of a seed in Hydatella may well be an apomorphic feature of Hydatellaceae alone but, given the newly discovered phylogenetic position of this family, potentially represents a plesiomorphic and transitional condition associated with the origin of flowering plants from gymnospermous ancestors.