Since this old thread has reawakened, I just thought I'd add: as a general rule, African gumvines (Saba, Landolphia, Clitandra, etc) can grow as either a shrub or a vine, and are usually shrubby when small or when there's no tree nearby. They're generally drought tolerant and while they tolerate shade, they can usually also take full sun even as a seedling, and grow significantly faster in those conditions. They usually tolerate poor soil and are drought tolerant.
Of course, they vary from species to species, but these are some "general rules".