Its easy to confuse the leaves of............

[veggiechicken]

Cosmos and carrot seedlings
Vinca/Periwinkle and Kiwi issai
Cultivated blackberry and wild blackberry
Brassica seedlings and Herb Robert when both are at the 2 leaf stage.

Just saying - as I've come across all of these today.

[Mr Bones]

It's also easy to confuse..
Young chervil and hemlock (could be fatal )
Lemon grass and rye grass (have nursed the latter thinking it was the former )

[jackarmy]

Pyramid and circular ( in bag form of course )

[veggiechicken]

You "tease", Jack.

[HoneyChild]

Teasel and borage

[Lumpy]

Spring onions and grass from bird seed scattered willy nilly for the daft critters during the winter.

[scarey55]

Parsnips and weeds. I managed to weed out all my parsnips one year

[Jay-ell]

Self sown Sand leeks and grass. Had a bag of weeds smelling suspiciously of leek.

Quinoa and fat hen.

[jackarmy]

WEED and WEEDS

[Vince G]

Cow parsley and hemlock (gulp)

[elsie-scot]

This will be just me -I thought I had a great patch of self sown calendula growing until the tops went spikyish. Turns out all lasts years calendula have had no babies, but the one M0rris0ns centurea has had quite a few!