Galium tricornutum aka Corn Cleavers

Galium tricornutum, commonly known as rough corn bedstraw, roughfruit corn bedstraw, and corn cleavers, is a species of flowering plant in the coffee family that is found across most of Europe, northern Africa and southern Asia. It has also been naturalized in Australia, the Canary Islands, Mauritius, Madeira, Réunion, Brazil, Argentina, and scattered parts of North America (mostly California and Oregon). This annual herb forms tangled masses or spreads thin and has stems that are sometimes nearly square in cross-section. The leaves are arranged in whorls of 6 to 8 around the stems and are bordered with prickles. White, thin clusters of flowers appear, followed by pairs of spherical nutlets that hang in the leaf axils. It might be poisonous, but corn cleavers is actually a super rare houseplant that needs regular watering to thrive and direct sunlight. If properly maintained, corn cleavers should not need adding fertilizers as it doubles in size. To get rid of it, you can try to manually pull it, or use a weed wrench, although these will not be effective against weeds with deep underground stems.