Plant identification: Asiatic Dayflower

(Question)

I received a cutting of this plant from my neighbor. He called it “portuguese water grass”, for which I can find no reference. It is winter hardy outdoors, spreads prolifically (from 3 small cuttings last spring, it now covers almost 4 square metres). It’s growth habits remind me a lot of “Tradescantia zebrina”.

What might this plant be?

(Answer)

 

It looks like your cutting is from the Asiatic dayflower (Commelina communis). It is an annual which can form new plants vegetatively and is a ¬†vigorous spreader. Keys to identification are blue symmetrical flowers with two prominent petals (the third, a tiny white one, is difficult to see), long fleshy leaves that attach directly to a red stem, and long creeping stems that point up at the ends. Each pretty flower lasts only a day. You are right to be reminded of Tradescantia–both belong to the same family, Commelinaceae.

While it is quite ornamental and potentially useful as a herb and vegetable, Commelina communis is also considered a weed as it thrives in open, disturbed areas, along roadsides and woodland borders. It is listed as an invasive in Kentucky, and as a troublesome or common weed in the states of Virginia, North Carolina, Georgia, Alabama, Louisiana and Florida.