Hibiscus trionum, commonly called flower-of-an-hour, bladder hibiscus, bladder ketmia, bladder weed, puarangi and venice mallow, is an annual plant native to the Old World tropics and subtropics. It has spread throughout southern Europe both as a weed and cultivated as a garden plant. It has been introduced to the United States as an ornamental where it has become naturalized as a weed of cropland and vacant land, particularly on disturbed ground.