Help about search fields is available. Multiple choices within most categories are OR 'd together, so you can search for plants with green OR white leaves. But this is not possible with this short form that uses standard HTML input boxes that allow only a single choice per item. Advanced searches are possible. For example, the habitat item lets you list plants that grow in disturbed areas AND full sun.
Special characteristics works the same way.
Multiple choices between categories are always AND 'd together. Blank fields are ignored, and recommended. An empty form will return everything. My advice is to start general and narrow it down with successive options. Burned Disturbed Roadside Press Search to submit this form, or Clear to reset everything.