To expand upon the Webster's definition, heterogamy has a couple of slightly different meanings in botany:
- The condition of a flowering plant species having two or more types of flowers -- for example, flowers which have only male parts along with flowers which have only female parts. Heterogamy is the opposite of homogamy.
- The condition of a flowering plant species having both the male and female parts of the flower mature at the same time, so that the individual flower can potentially pollinate itself. (Some species have come up with other obstacles to prevent self-pollination, however.)
Based on work I did for the science dictionary at http://biotech.icmb.utexas.edu/