Unknown Spotting ( Tiny Green Plants - No. 2 )

Description:

My front door mat, had tiny green plants, growing on top of it. The first time, these tiny green plants, was growing on top of the front door mat, was around June 4, 2017. Some time later, all these tiny green plants, disappeared. About a week later, some of these tiny green plants, started growing back again. This will be the second time. All these plants stayed tiny. These plants did not get any bigger. Now, there are two, tiny green plants, with four leaves on them. Now, there are about seventeen, tiny green plants, with two leaves on them. These tiny green plants, are growing again, on top of the front door mat, for about one and a half weeks now.

Habitat:

I looked out of the left front window of my house, and I spotted some of these tiny green plants, growing again, on top of the front door mat.

Notes:

I looked out of the left front window of my house, and I spotted some of these tiny green plants, growing again, on top of the front door mat. This is the second time this has happened, during the month of June.