Weed With 4 Petal White Flower . Photo by erin hill, msu. 45 types of white flowers with pictures flower glossary. identification What is this fourpetal lavender to white flower from gardening.stackexchange.com White flowers with three petals (½) on greatly branched stems. This cool season biennial herb is one of the most invasive lawn weeds with little white flowers. These plants all produce flowers on upright stems.