Where are you located? You can post pics directly by using the photo icon, people sometimes do not want to open what they are unsure of. I did open them but I do not recognize it.

If you do not get a response there is another forum here that you can also post to Name That Plant

The images are essentially the same -- only showing one leaf.

Please post an image of the entire plant.

I apologize for that.

I am located in Southern California. Most noticeable about this plant is the red midrib.

Perhaps a Medicago species. I would think something in Fabaceae at least.

I think the longer petiole on the middle leaflet is diagnostic of Medicago sp. vs. Trifolium sp.

Yellow flowered Trifoliums also have the stalked central leaflet, but this looks more like a Medicago.

Medicago is alfalfa. We have both alfalfa and "sweetclover" (Melilotus) and they look almost identical (and like your photos) until they start flowering. Melilotus dies after a couple of years, but self-seeds vigorously like a weed. Alfalfa, which we want more of and is perennial, doesn't self-seed as vigorously.