Lately I've been mowing and trimming the lawn regularly, especially since the new American-made mower
is a pure joy to use. I left one corner untrimmed for a couple rainy weeks, and found several of these had sprung up.
Never seen it before. Looks more like a schematic of a plant than an actual plant.
The stem is dark and brittle, about 18" tall, full of sticky milky sap. The base (not shown) has a circle of soft mint-like leaves.
Most weedy plants are extravagantly generous. They toss dozens of leaves and hundreds of bright flowers into the world, betting it all on pollination. Not this dude. He's stingy and grumpy like me. "I'm gonna put up just six
drab little flowers, and if you damn bees aren't sharp enough to find them, it's your own damn problem. Don't come buzzing to me, or I'll really give you something to buzz about!"
= = = = =
Later: Googling "weed dark brittle stem" pinned it down instantly: Fleabane.