Barriers to Self-Fertilization Flowers can be staminate (bearing
only male reproductive organs), pistillate (bearing only female
reproductive organs), or perfect (bearing male and female
reproductive organs). Individual plants can be monoecious
(bearing staminate and pistillate flowers), dioecious (staminate
and pistillate flowers borne on separate plants), or even
trioecious (staminate, pistillate, and perfect flowers borne on
separate plants). Within dioecy, various conditions can be found
in different species; gynodioecy, for example, is the term
applied to the breeding system of species in which individuals
bear either female or hermaphrodite flowers (Richards, 1997).
Almost three-quarters of all plant species produce perfect
flowers. Approximately 5 percent are dioecious, and slightly
more than 5 percent are monoecious (Molnar, 2004). Pollination
can occur within the flowers of a single plant, among different
flowers of a single plant, and among flowers of different
plants. A plant that is self-fertile a