The classic case of distinct tree genders is the ginko, where only the male trees are used for landscaping purposes because of the strong and (to many) unpleasant odor of the fruits. And it isn't uncommon for plants (such as the cucurbit family) to have distinct male and female flowers--which usually bloom at different times on a particular plant to help ensure cross-polination. I'm sure there's some technical term for each of these phenomena but I"m a zoologist, not a botonist.