I am systematically growing Cave Blossoms, with no luck so far. I fear it may not be possible given the flower colours/gradients coded into the game. The seed range of Cave Blossoms is <050 0000> to <059 9999> so there are 99,999 unique Cave Blossoms to find!
That said an monochromatic Tiny Tree may be possible, but I'm unsure if black is a option for Fancy Stem Colour.
edit: added bit about Tiny Tree
edit2: accidentally a word