Plant/weed ID

The Oxalis aren't a weed.
You would have bought forms for them.

 

...agreed. It's a garden plant that some people like...but has a nasty habit of spreading to where it's unwanted. I bought a house that came with 2 species of Oxalis. Despite a concerted effort to eradicate them, both still pop up all over.

 

3) The pink flower seems to come from a stem in the background which @Cinnamon and @Silver surfer confirmed as part of the Oxalis family. All types of Oxalis are opportunists and can spreads like wildfire in the right condtions. Yellow sorrel (Oxalis corniculata) is a real pain as it has exploding seed pods. Hopefully your version doesn't, as many types delevop bubils/small bulbs underground alongside the main tuber, and if the soil is disturbed, can cause the bubils to disperse and take root (somewhat like Lesser Celandine... which is unrelated but a serious pain in the backside... although in a higher league of invasiveness).

The main foliage in the bottom of the pick looks to me like creeping buttercup (Ranunculus repens) and if your borders are near a lawn, I'd be sceptical about keeping it as it's easy enough to dig up (use a fork... even just a small hand fork to remove all the roots more effectively than a trowel or spade) from borders but it can be a real pain eradicating it from lawns (assuming you have an adjacent lawn), without digging up grass as well as the buttercups.

Weed and feed usually kills it but often only if applied in the correct manner. The foilage needs a good week or longer after mowing in order to regenerate sufficiently to have the surface area required to make the product effective.

 

Sorry if it seems like teaching gradma how to suck eggs!

The most common types seem to be yellow sorrel with dark brown/blackish leaves and yellow flowers or wood sorrel with green leaves and yellow flowers. There's debate over whether they are the same species or subspecies of one another. Both seems quite resilient to Glyphosate, unless you make a nice mixture.

I find the green variant easier to fork out as it has shallow tubers and always bin the soil surrounding it so that the bubils don't fall off. With yellow sorrel, the roots are more rhyzomous and if given enough time, they form a taproot. Damn those things.... they crop up everywhere in certain gardens and are a real menace, particularly on fortnigtly jobs when they can flower and go to seed so quickly at this time of year.