Wildlife Spotting

This persistent weed looks like this every time it pops up around my backyard. It can get very tall in just one week. In addition to growing up in bare soil and amidst other weeds, it also pushed itself up right through the center of my dense lavender bush in quite a few locations. Its stalk beneath the ground is always moist and always seems to be attached to thick moist sideways plant matter covered in dirt way down in the soil, about 1 foot down (or maybe I'm exaggerating in my dismay). But when I try to get down to remove that old plant mass that's spawning these scary things, the moist stem quite often breaks before I can find the source. Nobody I've asked in person has ever seen it before. Please help me ID this thing?