One of my neighbours lent me her backyard plot for gardening this year, and letting it overgrow with… whatever last year. While I can identify most of the volunteer plants that are growing there, this one is stumping me. I’m fairly certain it’s something in the squash/cucumber family, but I don’t quite know what it is. It’s paler green than all the other things like it that I’m growing, for one. If it’s going to produce something that I’ll want, I’ll leave most of them out there since it’s mostly out of the way of my rows. Any master gardeners out there know what it is?
Rub a leaf and see if it smells ‘minty’. The leaves kind of have the look to them of various mints, but hard to tell from just this alone. Its a long-shot guess, of course.
Nope, no mint odor. It has almost like a faint fishy smell to it. The leaves also feel thick and spongy, and are covered in small “hairs”.
Where do you live?
What shape is the stem? Does it have any flowers? Do the leaves come off in opposing pairs, or do they make a spiral up the stem, or something else? Does it grow from a single stem out of the ground, or a rosette or a clump or does it start single and then branch off?
Is it really soft, like you want to pet it? So far, my guess is that it’s a baby comfrey, but it’s just this side of a WAG until you can share more details.
Calgary.
Cylindrical and smooth.
None of the plants have them yet.
Opposing pairs.
Single stem, although it hugs the ground quite closely.
It’s fairly soft, yes.
Hm. No more, mature, plants to photograph?
Try a net search on fuzzy/indigenous/Calgary/herbs/weeds/plants.
The reason I’m going here is that there are edible, if not desirable, young plants that only pop up in a short proper season for harvestong. Like burdock here in the deep south of NYC. 
And then there are those plants that will kill you just by touching them.
It’s true.
This is a seedling.
A kajillion plants look similar as seedlings.
Give us a phot in two weeks maybe I’ll have a clue.
Go over the observations in post #5 again then as some might change–practically all dicots start out with opposing pairs but some wind up spiralling, for instance.
Hmm, not comfrey then. Its leaves grow in clumps, not opposing pairs…
And not a mint, those have square stems…
It’s really, really hard to identify a plant before it flowers. Not least because the most common field guides begin the process with flower.
The good news is, there are several plant ID courses at the Calgary Zoo! 
Comfrey seedlings begin with opposing pairs, as nearly all dicots do.
With a dicot, there a two seed halves which each produce a leaf, naturally opposing.
Nevertheless, the mystery plant is not comfrey.
As others said, hard to tell at this early stage, but assuming it’s a volunteer of something that survived through composting of kitchen/household waste, then cucurbits are a strong possibility, or maybe sunflower.
If the plant is emerging from the soil with already-large/thick cotyledons (seed leaves) and an already-thick stem, this suggests that it’s growing from largish seeds (which again, cucurbit or sunflower would fit).
Are any of the seedlings emerging with the seed coat still wedged on top of the seed leaves? If so, that would be something to examine.
None that I’ve seen. I’ll come back to this thread when they’ve flowered.
By the time they’ve got another half dozen leaves, it should be easier especially if they’re one of the two possibilities I mentioned.
If its leaves have a cucumber-like fragrance when crushed, I’d vote for it being borage.
Cucumber seedlings seem to have leaves with more of a polygonal/hexagonal shape.
True, but not necessarily so for the first few true leaves - for example, thissquash seedling will probably have somewhat palmate leaves later on, but it seems that for a lot of plants, leaf shape is simplified at the early stages of growth.
I think this might be right. I was walking through a greenhouse today and saw some borage, and it looked very similar to what I’ve got out in the garden right now.