Sentence:  Further, species which show continuous variation that is not amenable to orthodox taxonomic treatment, and this is the situation in many <WSD>monoecious</WSD> plants, are treated as invariable. 
Meaning of the word marked with <WSD> tags:  That has male and female reproductive organs on the same individual plant (rather than on separate individuals), either in different flowers<ref name=Hick01>Hickey, M. & King, C. (2001), "The Cambridge Illustrated Glossary of Botanical Terms", Cambridge University Press</ref> or in the same or different flowers<ref name=Beentje>Beentje, Henk. (2010), "The Kew Plant Glossary", Richmond, Surrey: Royal Botanic Gardens, Kew, (978-1-84246-422-9)</ref>