This is yellow nutsedge (Cyperus esculentus), a member of the sedge family. Nutsedge's triangular stem is one of the main clues that this is not a grass -- grasses have round stems. Nutsedge is a perennial, plant that reproduces mainly by underground tubers (nutlets), which can remain dormant in the ground for several years. For this reason nutsedge is difficult to eradicate, and is considered a common lawn and garden weed. Nutsedge thrives in low spots and high moisture areas that drain poorly, but can occur in drier sites as well.
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