Kitniyos is not chometz and may be kept over Pesach; Sephardim have the minhag to even eat kitniyos on Pesach. Thus, kitniyos does not need to be sold to a non-Jew. However, some are machmir to mention kitniyos in the document since one of the reasons Ashkenazim are machmir for kitniyos is that perhaps some pieces of chometz got mixed in (see Issue 129, paragraph 7) (שו''ת דברי מלכיאל ח''ד סי' כ''ב אות ה'). Nevertheless, there is no need to mention kitniyos explicitly since if there is indeed chometz among the kitniyos, it is already included in the general wording of the sale which includes any concern of chometz or possible chometz.
Mustard
Mustard is a type of kitniyos, but sometimes it contains grain flour too, so it should be included in the sale.
Quinoa
Quinoa is considered kitniyos, so Ashkenazim should not eat it on Pesach (see Issue 129, paragraph 29), but there is no concern of chometz.
