This is correct that we have a parent plant that covers all plants in the Viburnum genus, and a plant cannot be a child to multiple parent plants. This means that we can't make Viburnum dentatum (pid 79475) a parent plant since it is already a child.
What we did in hibiscus was to make no parent plant on the top level but have several parent plants on the species level, and that worked out very well.
Being able to share data points across multiple plants is the primary reason I created parent plants in the first place, but parent plants are currently the only possible way to automate adding data points across multiple plants.
