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Species within the genus Pseudowintera exhibit high rates of self-sterility. Self-sterility in the genus has been previously posited-but not confirmed-to be the result of late-acting ovarian self-incompatibility (OSI) functioning within nucellar tissue of the ovule to prevent self pollen tubes from entering the embryo sac. Structural and functional aspects of pollen-carpel interactions and early seed development following cross- and self-pollination were investigated in P. axillaris to determine the site, timing and possible mechanisms of self-sterility. No significant differences were observed between pollen tube growth, ovule penetration and double fertilization following cross- and self-pollination. Pollen tubes exhibited phasic growth in an extracellular matrix composed of proteins and carbohydrates, as well as arabinogalactans/arabinogalactan proteins. A uniform failure in embryo sac development prior to division of the zygote was apparent within 15 d following double fertilization by self gametes. Results indicate that SI mechanisms in P. axillaris do not prevent double fertilization from occurring. Instead, mechanisms of self-sterility affect post-zygotic development of the embryo sac. Although self-sterility may be attributed to inbreeding depression, given the post-zygotic nature of failure in embryo sac development, the possibility of late-acting OSI is discussed.

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Aniborella iricliopoda Baillon is a vesselless New Caledonian endemic in a family of its own, the Amborellaceae. Pollen is boat-shaped-elliptic to subglobose and small to medium sized. I t is mono-aperturate, heteropolar, with the aperture probably at the distal pole (anaulcerate to anasulcate) or apolar and inaperturate. Inaperturate pollen appears to have evolved incompletely in Alnborella. The exine has ornamentation of a gcmmate-like appearance but consists of small cupules constructed of coiled cylindrical strands (ca. 100-130 nm diameter), bearing small spines. The sexine is ca. 0.5-1.0 pm thick and overlies a foot layer 0.2-0.4 pm thick. An endexine is absent. The intine has an outer zone containing tubular material within and adjacent to apertures. Pollen morphology supports the retention of the Amborellaceae as a separate family, within the Laurales.Horroriia is a Sri Lankan endemic of 3 species comprising the Hortoniaceae or subfamily Hortonioideae of the hlonimiaceae. Pollen is inaperturate (omniaperturate), isopolar, spherical, small to medium-sized, with hemihelical bands of exine thickening radiating from two "poles". Each band is constructed of interwoven cylindrical strands ca. 80-200 nm diameter. This unusual cxine has no tectum, columellae, foot layer or endexine. Between and beneath the exine bands there is a thick intine with an outer zone containing tubular material. Pollen morphology of Hortotiia emphasises its isolated position but also suggests links between the Lauraceae and Monimiaceae.

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