Common Chickweed

Classification:
Kingdom: Plantae
Division: Magnoliophyta
Class: Magnoliopsida
Order:
Family: Caryophyllaceae (pink family)
Genus species: Stellaria media

Plant Description:
Flowers are white, small. 
Flowers have five petals but petals are so deeply cleft that flowers seem to have 10 petals. 
Sepals are longer than petals. 
Leaves are short, ovate.

Photo sources:
Vanessa Fox, DePauw University
http://commons.wikimedia.org/wiki/Image:Stellaria_media_2003-02-04.jpg