The frequency, distribution and reproductive biology of dioecious species in the native flora of Britain and Ireland

The proportion of dioecious species in the flora of the British Isles has been underestimated in the past, partly because the total number of native species was overestimated and partly because some dioecious species were omitted for various reasons. We estimate that, in a total native angiosperm flora of 1377 species and species-equivalents, 4.3% (59 species) are dioecious, a substantially higher percentage than the previous estimates of 2, 3.1 and 3%. If gymnosperms are included, 4.4% (61 of 1380 species of seed plant) are dioecious. A review of published work shows that few of these dioecious species have been well-studied, and that for some little or no information is available about their sex ratios and reproductive biology.