shp123, found this on google, never having grown mustard greens before, and it sure looks like similar..

mustard greens plant - Google Search · More Info

I may watch it to see if it goes to seed, forms pods.

Yes, a mustard or, possibly, a turnip.

Chard is glossy and smooth, not toothed and rough and it has distinctive white midribs.(In green varieties).

Thank you floral. I noted white ribs on the plant, and that's why my mind went to chard, but the leaves were just too spread out.

If I knew for sure it was mustard greens, we'd be eating them. Oh well. No way to know without some doubts.

Mustard , specifically Florida Broadleaf. Taste a leaf, mustard has a distinctive pepperary flavor and FB is one of the stronger flavored varieties.

Can't stop myself, running out there right now to take a taste...

farmerdill, just as I saw your comment, Bakers Seeds, where I ordered the broccoli and other seeds also sent an email saying to take a taste. It's not mustard greens. Very, very mild flavor, quite pleasant.

I'm totally stymied, as I'd found a photo of the FL broadleaf you mentioned, and it's so similar. The fellow at Bakers Seeds saw the same photos above and said "Looks to me like Rapini Raab. If I'm right, you should be seeing a flower stalk pretty soon. You let this grow, then harvest when the first flower bud on it begins to open. It's eaten like broccoli (yet technically a turnip), although a single floret will only give you a taste. If no flower head develops soon, feel around the base of the plant, and if you feel a root developing, it's a turnip. If no flower head and no turnip, it could be a mustard. A taste of a leaf will tell the tale there."

So, my quest continues.

Edited to correct: Baker Creek seeds. I have to add, I was pleasantly surprised to get an email response from them!

The ribs are nothing like the ribs of chard which are broad and white, almost as broad as celery. Often an inch across. Totally different. Nor is the leaf texture and colour remotely like chard. Its 100% not chard which isn't even a brassica, which your plant is. It's a mustard of some kind, or possibly, but unlkely, a turnip.

That is good customer service. I would rule out broccoli raab as it has the same dark color of turnip greens. The only other mustard green leafy vegetable that I know is Chinese cabbage (NAPA or Michilli) That is mild and sweet.. Broccoli raab is slightly bitter like turnip greens..

From Baker's Creek Seeds, they have this mild mustard...
Miike Takana Mustard?

I am not familiar with this variety, But if you got your seeds from Baker Creek, There is a good possibility that one of these seeds got mixed in your order. It is not a common variety. They don't list a scientific name but it is most likely an Asian variety

I don't think it's the Miike Takana as it's not got the bubbly texture. I've assumed it was a stray seed from something else they sold, but have since seen a photo posted of Holland Greens, and that's pretty identical to what I have. Baker's doesn't sell that seed, but as it seems to be used as a ground cover sometimes, I think it might be a possibility.

Possible. Tyfon is a cross between Chinese cabbage ( Brassica rapa Pekeninensis ) and Stubble turnip. Tyfon/Holland Greens are palatable and mild flavored according to reviews. They will self seed when used as a pasture or cover crop. Not widely planted in the US tho.

When I saw your pics, I thought it looked a lot like my plants. Spring Raab Rapini Broccoli from Sustainable Seeds.

CathyCA, well, now I'm very confused. Just as the Holland Greens looked like what I've got - see below:

Vegetable plant ID help – Cauliflower, chard? I don’t know! (x post) · More Info

now so does your photo. As you can see, they are so alike. At this point, I think I will watch to see if they grow a small head. The people at Bakers said it might be rapini raab. Thus far, it just keeps getting bigger and bigger, spreading out, unlike the Waltham 29 broccoli I planted, which is growing upright. Of course, I knew it wasn't that.

Fun mystery plant. Mine are large as well and spread out.

Rapini is a type of turnip. Leaves should have a slightly bitter after taste.

Well in any case, it certainly looks edible -- whether you call it mild mustard greens, turnip greens, or immature rapini. That whole family is edible, and when it happens to be mild, it is imminently so. If it's crowding out your broccoli, you could just cut off the big leaves, chop 'em up, saute in some oil and onion or garlic, and it will almost surely be delicious and nutritious. That's what I would do.

In fact, I did that, when something grew in my garden mulch several years ago that seemed to be a mustard green. It turned out to be milder than my arugula, so I ate some, let it go to seed, and have been planting it ever since. I think it must have grown when I threw the trimmings from a pickling episode onto the mulch. But I tried planting what I thought were the same mustard seeds the next year, but they were rougher and less tasty than the mystery mustard greens, so I don't know where the first seeds came from, but I keep planting them.