Any mushroom expert around here?

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Oxalis corniculata. It's an extremely invasive weed. It sends down deep rhizomes. It shoots ripe seed well over 3 feet / 1 meter.

We didn't help rbarata at all. But he took great photos showing most of the important characteristics for identifying mushrooms:

Are there gills or pores under the cap?
Do the gills stop before the stem? Just attach to the stem? Run down the stem?
Does the stem arise from a cup, or directly from mycelia?
If from a cup, do remnants of the cup tissue remain on the expanded cap?
Does the cap liquefy from the edges in as it ages?

Only one remains - what color are the spores? Set the cap on a piece of white paper. Spores fall onto the paper. Their color is important for diagnosis.