Stellaria Media (Common chickweed)
Image credit: Clarence E. HsuIdentification tips
Tip #1: to remember the scientific name, the name of the genus comes from the Latin "Stella" meaning star, the flowers are very reminiscent of a star and the name of the species comes from the Latin "media" which means it kind of has to do with the size of the species, just remember that it is born in the middle of the crop.
Plant shape
2º Identification tip: usually the plant grows in a prostrate way, and can emit roots in stem nodes. It may grow upright too, but it's less common.
Leaves
3º Identification tip: the leaves are oval and opposite when they grow they can show ripples on the sides of the sheet without changing the margin of the leaf.
Stem
4º Identification tip: the stems are fundamental for identification of this species, these have thin hairs in a parallel line and change direction to each node, forming as if it were a spiral along the stem. These hairs are also present in the petiole and in the gems.
Flowers
5º Identification tip: the flowers are also one with identification indicative of the species, the star shape of the sepals is very characteristic, accompanied by the divided white petals.
Seeds
6º Identification tip: the seeds have a reddish color and look quite different, resembling a dinosaur skin or something like that.
Although they are quite peculiar, the seeds are very small, making it difficult to observe this characteristic with the naked eye.
Seedlings - the terror of all
7º Identification tip: cotyledons are shaped like a spear, hairless. They have short stems with sparse hair. The first and next pair of leaves are oval, with small tips at the tips and have short stems with a line of hair down on both sides.
Extra references:
http://identifythatplant.com/stellaria-chickweed-species/