The Kefir plant is a combination of yeast and bacteria - not a plant as
such. We use the same term in the UK for a culture used for making
ginger beer, it is called a ginger beer plant but it is still a yeast.
Suggest you try the microbiology list. Warning, experience of a
colleague many years ago suggests that making Kefir (the "culture" is
also sometimes called "Kefir grains") is not that easy and when it goes
wrong the product is quite disgusting !
University of Reading,
AKA <P.J.Harris at reading.ac.uk>