You searched for: “liken
lichen, liken
lichen (LIGH kuhn) (noun)
One of several thallophytic (Lichenes) that are crusty patches or bushy growths on tree trunks, rocks, or on the ground, etc.: The lichen on the dead branch of the hedge was multicolored and fascinating.
liken (LIGH kuhn) (verb)
To compare as similar: In Jeff's poem, the author tried to liken the shine in Diana's eyes to the stars in the sky.

It is a fair comparison to liken mistletoe to lichen since they both grow in a symbiotic relationship with their hosts.