Weeds of Wednesday: Common dayflower

Terry Greene (Class of 2019) asked about this tiny blue-flowered plant that we saw at Treasure Shores Park growing amid beach dune sunflower (Helianthus debilis).  It is a dayflower, most likely common dayflower (Commelina communis).  Each flower lasts only a day.

The genus name, Commelina, references two 17th century Dutch botanists, Johan and his nephew Caspar Commelin.  The species name, communis, means wide-spread.

Common dayflower is a much-hated common weed of Asian origin.  It laughs at herbicide, and even the tiniest piece left behind will re-sprout.

The native whitemouth dayflower (Commelina erecta) looks quite similar flower-wise (2 big blue petals & small white petal) but has an upright growth habit to which the species name, erecta, refers.

Whitemouth dayflower prefers drier locations.  The photo above was taken at the Wabasso Scrub on a 11-11-2018 walk and has not been found growing at south Oslo Riverfront Conservation Area.

Plant ID matters!