Keys are made so anyone can go through the crucial features in order to select those plants (or anything the keys are designed for) which fit the bill. e.g., if it has flowers you choose the colour; tree, shrub, herb etc.; type of leaf e.g. simple; leaf edge e.g. serrate. You don't have to fill in all the fields, only those you know.
Try it on the search link of txflora.org, the site will automatically select once you have chosen each feature. These are easy compared to for example diptera keys!
http://txflora.org/Search.aspx...
