I hadn't noticed this before, great question. Wumbea plants aren't actually male or female but can alter their sex depending on resources - not sure if they are self fertile but this paper has more info https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3278287/
There were many more male than female flowers (~90%), very small number of hermaphrodites (~1). Those plants that were female occurred in small clumps. Often there were no females to be found in a vast array of males.