My first thought was Scirpus atrovirens (dark green bulrush). However the red at the base of the stem does not fit this species but might suit Scirpus microcarpus (panicled bulrush).

Neither one likes dry conditions though, so it may be another Scirpus sp.

It is hard to tell the scale of the picture; in other words, I can't tell how tall the plant is, but it looks a lot like a sedge in the genus Cyperus. These are usually called Nutsedges for the nut-like nodules on the roots. They are native, but a weed in gardens. There are several species, I think.

Thank you all for the help, it definitely pointed me in the right direction. After lots of internet reading I'd call the plant the Panicled Bulrush, Scirpus microcarpus.