Arabica is a self pollinating plant, where Robusta is cross-pollinating. Cross pollination gives more variety and as a result larger differences in bean types, and ultimately flavor. Self pollination allows the variety to remain the same with less mutations, giving a more consistent bean production. Arabica beans are slightly larger and more oval-shaped while Robusta beans tend to be much smaller and more rounded. While the shapes don't necessarily make any difference in taste, they act as a sort of spot check when importing new beans from a farmer.
