This parasitic plant turns up every year in the marjoram plants we grow at work, and only ever in the marjoram. I’m pretty sure the marjoram seeds are contaminated with dodder (Cuscuta) seeds.
This is how it starts, a few thread-like stems, leafless and rootless, sucking what they need from the marjoram plant.
And this is what it turns into.
Tiny tiny flowers (and my work-dirty fingernail).