Yes - its because Landcare has yet to update their Cyperaceae treatment. You see Baumea is morphologically, cytologically and otherwise speaking indistinguishable from Machaerina. Ever wondered why Baumea complanata looks like Machaerina sinclairii? Well now you know!!! Last year I learned that everyone else in the world has rejected Baumea in favour of Machaerina - the work of Koyama is now followed. I made the switch on the NZPCN Fact Sheets last year after attending the Cyperaceae sessions at the Botanical Congress, hearing about this and discussing it with the worlds leading Cyperaceae experts.
I should also add that Landcare's Plant Name Database is a resource based on the names used in the NZ Flora series and the Allan Herbarium. As such it does not necessarily reflect other, more recent (or past) taxonomic opinions.
Cheerio
Peter J. de Lange