I have quite a growth of a very low lying weed all around my onions.

It has very shallow roots - grows about half an inch high. Has spikey
(but not sharp) leaves - about 1mm wide.

Small flowers which have four petals - yellowy/whitish/green - about
4mm across.

It is not chickweed (flowers not right)

Any suggestions I can look up photos of please?

(The onions are fine !!)