Pimelea Arenaria, an endangered native sand dune plant, appears to be experiencing recruitment failure. The structure of four populations from the lower North Island, New Zealand, was examined for recruitment patterns, while one population was examined for flowering, pollination, and seed germination limits on regeneration. Line transects and searches found no seedlings, and measures of individual plant sizes (n = 331) showed bias towards medium, with some large, individuals, suggesting recruitment failure at all sites. Flowers are plentiful. The standing crop of nectar was c. 0.4-0.9 joules per hermaphrodite flower, with insects appearing to be the main pollen vectors. Pollination manipulations were carried out on both genders at one site, with fruit set measured from natural, hand out-crossed, and pollinator-exclusion treatments. Female flowers do not appear to be pollen-limited as the natural fruit set is only non-significantly lower than that in hand-outcrossed flowers. Only hermaphrodite plants selfed autonomously, with nearly 90% producing fruit. One-quarter of the seed from both female and hermaphrodite flowers germinated. Results suggest that recruitment failure of Pimelea Arenaria is not due to reproductive biology, pollen limitation, or poor seed germination. Therefore, recruitment failure probably occurs during the seedling establishment phases, due to environmental pressures and/or predation.
