Unique stigmatic hairs and pollen-tube growth within the stigmatic cell wall in the early-divergent angiosperm family Hydatellaceae.

Background And Aims: The ultrastructure of the pollen tubes and the unusual multicellular stigmatic hairs of Trithuria, the sole genus of Hydatellaceae, are described in the context of comparative studies of stigmatic and transmitting tissue in other early-divergent angiosperms.

Methods: Scanning and transmission electron microscopy and immunocytochemistry are used to study the structure and composition of both mature and immature stigmatic hair cells and pollen-tube growth in Trithuria.

Key Results: Trithuria possesses a dry-type stigma.

A new type of specialized morphophysiological dormancy and seed storage behaviour in Hydatellaceae, an early-divergent angiosperm family.

Background And Aims: Recent phylogenetic analysis has placed the aquatic family Hydatellaceae as an early-divergent angiosperm. Understanding seed dormancy, germination and desiccation tolerance of Hydatellaceae will facilitate ex situ conservation and advance hypotheses regarding angiosperm evolution.

Methods: Seed germination experiments were completed on three species of south-west Australian Hydatellaceae, Trithuria austinensis, T.

Seed fertilization, development, and germination in Hydatellaceae (Nymphaeales): Implications for endosperm evolution in early angiosperms.

New data on endosperm development in the early-divergent angiosperm Trithuria (Hydatellaceae) indicate that double fertilization results in formation of cellularized micropylar and unicellular chalazal domains with contrasting ontogenetic trajectories, as in waterlilies. The micropylar domain ultimately forms the cellular endosperm in the dispersed seed. The chalazal domain forms a single-celled haustorium with a large nucleus; this haustorium ultimately degenerates to form a space in the dispersed seed, similar to the chalazal endosperm haustorium of waterlilies.

Nonflowers near the base of extant angiosperms? Spatiotemporal arrangement of organs in reproductive units of Hydatellaceae and its bearing on the origin of the flower.

Reproductive units (RUs) of Trithuria, the sole genus of the early-divergent angiosperm family Hydatellaceae, are compared with flowers of their close relatives in Cabombaceae (Nymphaeales). Trithuria RUs combine features of flowers and inflorescences. They differ from typical flowers in possessing an "inside-out" morphology, with carpels surrounding stamens; furthermore, carpels develop centrifugally, in contrast to centripetal or simultaneous development in typical flowers.

Comparative ovule and megagametophyte development in Hydatellaceae and water lilies reveal a mosaic of features among the earliest angiosperms.

Background And Aims: The embryo sac, nucellus and integuments of the early-divergent angiosperms Hydatellaceae and other Nymphaeales are compared with those of other seed plants, in order to evaluate the evolutionary origin of these characters in the angiosperms.

Methods: Using light microscopy, ovule and embryo sac development are described in five (of 12) species of Trithuria, the sole genus of Hydatellaceae, and compared with those of Cabombaceae and Nymphaeaceae.

Key Results: The ovule of Trithuria is bitegmic and tenuinucellate, rather than bitegmic and crassinucellate as in most other Nymphaeales.

Seedling diversity in Hydatellaceae: implications for the evolution of angiosperm cotyledons.

Background And Aims: Cotyledon number has long been a primary morphological feature distinguishing monocots from other angiosperms. Recent placement of Hydatellaceae near the early-divergent angiosperm order Nymphaeales, rather than in the monocot order Poales, has prompted reassessment of seedling morphology in this poorly known family.

Methods: Seedlings of six species representing all eco-geographical groups of Hydatellaceae are described using light and scanning electron microscopy.