Can anyone help with this?

[prh47bridge]

This stuff keeps growing through my lawn. As you can see, it grows in clumps. These clumps are connected by a long, woody root. A couple of years ago my sons dug up the lawn and removed a huge network of these roots. That stopped it for a bit, but it is back. I used to just mow it but doing that doesn't stop it - the roots just get bigger. I'm currently digging it up and extracting as much root as I can, but it is a pain and makes a bit of a mess of the lawn. I suspect that this is coming through from next door - one of our neighbours just lets his garden run completely wild. Does anyone know what this is? And is there anything I can do to treat it and make it go away permanently?

It looks like garlic mustard to me, it's a common hedgerow plant. Supposedly edible though I've never tried it.

I get a bit in my back border, where it's usually quite easy to pull up. I'm a bit surprised by your description of a connected root system - afaik it's a biennial...maybe my identification is wrong. If you rub a leaf does it smell garlicky/mustardy?

But if you've got something with a root system you really want to eradicate in a lawn then I'd be tempted to use a systemic herbicide such as glyphosate - apply carefully to the leaves as it will kill grass if it gets on it.

I don't know but I have exactly the same growing in my lawn and have been wondering the same. It breaks quite easily but the underlying root system is massive. I've wondered if it's a type of tree but I have no idea.

Yes, that was my first thought, but Garlic Mustard has alternate leaves and this seems to have its leaves in opposite pairs. And, as you say, it doesn’t have that root system.

OP - is it possible to get an in focus close-up? And is the stem square or round?

@ErrolTheDragon Yes, garlic mustard is edible. It’s in the cabbage family, which is pretty safe to experiment with, unlike the pea or carrot families which have members which can kill you. Garlic mustard is good added to a mixed green salad, for a gentle hint of garlic. It’s not as strong as wild garlic.

Can you get some close-up photos of the leaves and flower spike, OP?

It looks like suckers from an Aspen or White Poplar tree to me - like Lilac, Cherry, Plum and many other trees they have an extensive root system which will spread many yards from the parent tree and will produce suckers from the roots. Do your neighbours have such a tree in their garden?

I'll see what I can do.

There are two large trees very close together in next door's garden. Definitely not Aspen, but possibly White Poplar.

White poplar sounds a good suggestion, but that also has alternate leaves - @prh47bridge, could you have a good look and tell us whether the leaves are alternate or opposite?

My son mowed the lawn yesterday, so closeup pictures of the leaves will have to wait for a few days.

I've decided I'm not very good at identifying trees 😊 The trees next door have a whorled leaf arrangement.

I have a snake bark maple tree whose leaves are a similar shape

It’s not garlic mustard, I’ve got it and it’s hugely invasive. It wouldn’t grow in those clumps and it doesn’t have woody elements or the root system.

They don’t sucker, though

More close up images as requested

Well, that doesn’t help much! It confirms the leaves are in opposite pairs, which rules out everything suggested so far