Reproductive cycles of two allopatric subspecies of Juniperus oxycedrus (Cupressaceae)

Reproductive cycles of Juniperus oxycedrus subsp. oxycedrus and subsp. macr ocarpa were studied during three consecutive years in southwestern Spain. T he two subspecies showed two-year reproductive cycles in which all the even ts were similar and synchronous. Pollen was dispersed in late October to ea rly November. Seed cones began to secrete pollination drops in late October : unpollinated ovules secreted until February. Cones in which no ovule was pollinated aborted. Pollen grains germinated in early February. Fertilisati on took place at the end of May or beginning of June, and seventeen months later, the embryo was completely mature. Unpollinated ovules failed to matu re. Some pollinated ovules aborted in late January, probably as a consequen ce of a failure in megaspore development. Many others aborted at the mature gametophyte stage, just at fertilisation time. Results are dicussed in rel ation to deficient pollination and low pollen viability or vigour.