Ovulate cone and seed biology of Wollemia nobilis (Araucariaceae) and comparison with Agathis microstachya and Araucaria cunninghamii

Context Most gymnosperms are dioecious (no self-pollination). It was not known if Wollemia nobilis (monoecious) could produce viable seeds via self-pollination. Aims In the nearly 30 years since its scientific discovery Wollemia nobilis (Araucariaceae) has been the focus of considerable scientific attention. While this includes several aspects of sexual reproduction, many features of ovulate cone morphology and seed biology have not been investigated. Methods Various aspects of ovulate cone morphology were quantified, as were seed morphology and germination (e.g. seed moisture content and rate of imbibition), in material from an isolated tree of Wollemia nobilis. Seeds of Agathis microstachya and Araucaria cunninghamii were also examined to allow comparisons across the Araucariaceae. Key results In Wollemia nobilis most seeds were empty (no formation of a megagametophyte and embryo (M + E)). Empty and filled seeds were morphologically very similar. On average, the fresh weights (FW) of empty and filled seeds were 6.2 and 33.1 mg, respectively. On average, the FW of the M + E was 25.8 mg (78% of seed mass, the other 22% was testa). The average moisture content (FW basis) of the testa and the M + E were 9.6% and 7.0%, respectively. The M + E imbibed water relatively slowly and imbibed, on average, to ~110% increase in FW after 48 h. In Agathis robusta and Wollemia nobilis the seeds separated freely from the cone scales. In Araucaria cunninghamii the M + E was an integral part of the bract/scale complex. Conclusions The seeds examined in this study came from an isolated, almost certainly self-fertilised tree. The seeds were of approximately the same dimensions as those from the wild populations of Wollemia nobilis, while average filled seed FW was greater and less variable. The filled seeds had a high viability and an excised M + E could germinate rapidly. This study shows that Wollemia nobilis can produce large, viable seeds via self-fertilisation. Successful self-fertilisation may be a factor in the low genetic diversity detected in the wild population. Implications Based on evidence from a single tree it would appear that Wollemia nobilis can produce large, viable, vigorous seeds via self-fertilisation. This has implications for the population structure of this species.