Viscum minimum, a tiny mistletoe, uses only Euphorbia horrida and Euphorbia polygona as hosts. The red fruit is only 8-9mm, with one seed inside, not much bigger than the seed of a tomato. The fruit provides an adhesive that sticks the seed to the stem, and when the seed germinates, it 'injects' itself into the plant. Most of the plant consists of branching haustoria which grows inside of the host, with only a few minute scale-like leaves to be seen on the surface. The flowers are too tiny to notice, but the red berries are wonderfully bright red against the white host.
It does not seem to hurt the host, so it is sometimes inoculated on the white stems of Euphorbia horrida cv 'Snowflake' as an attractive novelty.