The Birds and the Bees and the Flowers and the Trees

Given that about 5% of angiosperms are dioecious but only a few cases of sex chromosomes have been discovered this raises the question of how sex is determined in the rest of these species. I found this nice review in the journal Genetics last year:
The Birds and the Bees and the Flowers and the Trees: Lessons from Genetic Mapping of Sex Determination in Plants and Animals

Sex determination is an important area of study in developmental and evolutionary biology, as well as ecology. Its importance for organisms might suggest that sex determination is highly conserved. However, genetic studies have shown that sex determination mechanisms, and the genes involved, are surprisingly labile.