Pollination in Araucaria Juss

Abstract

Pollination was studied in three species of Araucaria: A. cunninghamii, A. heterophylla and A. bidwillii. More limited observations were made for A. hunsteinii and A. angustifolia. The investigation revealed considerable variation among species of Araucaria with respect to pollination features. The bract scale of the receptive cone of both A. cunninghamii and A. heterophylla has a stoma-free furrow which directs pollen grains onto a thin flange on the tip of the ovuliferous scale. The bract scale of A. bidwillii bears stomata over most of its surface, and is broadly scalloped so that pollen grains are deposited in a band across both bract and ovuliferous scales. On germination, the pollen tubes of these three species penetrate the epidermis of the scale and for a short distance grow beneath the surface before emerging and travelling, without branching or major deviation, towards the proximal end of the ovuliferous scale. On reaching the micropyle, the pollen tubes enter the nucellus. In known features, pollination in A. hunsteinii resembles that in A. bidwillii. The pollen tubes of A. Angustifolia bear short branches and, in distal regions of the scale, are erratic in their orientation. Results are discussed in relation to pollination mechanisms in other conifers and to taxonomic divisions within the Araucariaceae.