Variation in sexual reproduction in Taxus cuspidata Sieb. & Zucc

Abstract

Male and female strobilus production and seed production were measured in multiple years in three natural populations of Taxus cuspidata in Japan. Our goal was to record variation in these parameters among individuals, among populations, and from year to year in this species, which is defined as dioecious. We also wished to determine whether cosexual individuals occurred in the sampled T. cuspidata populations. Male and female strobilus production varied significantly among male and female individuals, respectively, and individuals had significant annual variation in male and female strobilus production. Significant variation in male and female strobilus production was also recorded in comparisons among T. cuspidata populations. In some populations, males were significantly larger than females, but this result was not consistently observed. No cosexual individuals were recorded in any of the populations studied. Correlations among reproductive variables and measured vegetative characters were generally non-significant at all sites and in most years, with a few exceptions. When compared with other Taxus species, strobilus ratios in T. cuspidata were less male biased (2.3 male strobili per female strobilus in T. cuspidata versus 8.7 and 7.0 male strobili per female strobilus in Taxus brevifolia and Taxus canadensis, respectively). Seed production efficiency was comparable to T. brevifolia, but less than half of that recorded for T. canadensis, the only species of the genus that has individuals that are typically cosexual.