This site is at an early stage, obviously. To select a plant attribute from the characteristic list, e.g. got to Longevity and click on annual. If you want to select more than one attribute, say biennial as well, CTRL-click on that; this searches for plants that are both annual and biennial. CTRL-click again to de-select. You can also search for the character itself without attributes, so if a plant has (or had) hairs but you aren't sure of the type, you can just select hairs itself. If the search is unsuccessful, the previous selections are retained. You can zero all selections by reloading the search page. Streamlining the form and general site functionality will be addressed in the next few months.
Also note the search form doesn't have all the characters in the database, it is too long and clumsy for all of them.
As there are only fifty-odd plants recorded so far, go to the home page and look at a few plants to get an idea of what is recorded. You can then do a new search and fill in the characteristic(s) you want to search for, for example {growth_habit: climbing} returns five plants.
Note that the characters are in a hierarchy, e.g. stem.leaf.attachment.petiole, to represent their physical relationships. These characters are represented in the search form with two underscore characters, so it becomes stem__leaf__attachment__petiole (this because of a quirk with the web engine). You can look for a characteristic in the form using these, so enter CTRL-F on your browser and search for 'attachment__petitole' instead of scrolling down and down and down.