For instance, we'd like to add the genus Cardiocarpus to the "Genera and species"-vocabulary.
Go to "Content" (right sidebar, scroll down) and click on "Taxonomy". A table with all the used vocabularies is shown. Scroll to the vocabulary which you want to extend. In this case: Genera and species. At the end of the row there are four clickable selections:
Editor; settings; list items and add aitems.
Now there are two possible ways to add a new term: 1.) via "add items" and 2.) via "Editor".
ad 1.) Click on Add items and you get a form with two visible fields: term name and description. Fill in "Cardiocarpus" in term name and click on save. Ready. If you want to add a species like Cardiocarpus tritolopus, you fill in Cardiocarpus tritolopus in term name, click on "Advanced options" and under "Parents" you start typing "Cardiocarpus" until you get a pulldown box in which "Cardiocarpus:[+ a number]" appears. Select that one and click on save. Ready. If you want the terms in a non-alphabetical order, you should choose "list items" and drag your term to the right position.
ad 2.) Click on Editor.
Click on the Add Term icon (the one with the green plus-sign). Fill in Cardiocarpus in "term name"-field and click on save. For adding a species to this genus, make sure that "Cardiocarpus" is selected in the list under the icons and click again on the Add Term icon. Fill in term name field and click again on save. If you want to change the order in the list, you can drag the term up and down by moving the cursor on the term (the cursor will change into something with four arrows) clicking down, moving to the right position and unleashing the mousebutton again. If you want the term to have the same rank as the one above it, unleash the mousebutto, while you hoover over the square of the term just above.