What is this weed?

Question

I started growing vegetable in my garden last year and have notced this weed that just keeps coming back. It grows out rather than up, and each stem has three heart-shaped leaves a bit like a clover or a shamrock, but they are dark green in colour, gradually changing to a deep blood red even purplish in places.

What is it and does anyone have any tips on how to get rid?

Answer 1

From the leaf shape it sounds like wood sorrel.  They grow on rhizomes so they will grow back unless you dig out all of the root.

Answer 2

I think it's Yellow Oxalis, Sleeping Beauty (Oxalis corniculata)

A fairly common garden weed that ought to be welcome for its ability to cover the ground in interesting reddish leaves and bright yellow trumpet flowers. Spreads rapidly, grows anywhere. Very difficult to get rid of, with tiny tubers and lots of seeds.  Good luck :-)