The leaves are 'more triangular,' as you say, technically
they are rhombic-ovate near the bottom of the plant and
lanceolate near the top. The leaves have a toothed pattern for their edges.
Sometimes the leaves are silvery on the underside, sometiems they are green
on both sides. (the greener ones taste more tender to me).
The main stem has grooves on it, and the top of the plant
ends up with clusters of tiny seeds as the plant matures.
It was once a European forage plant (Lois was asking about those)
which has now spread across the country, so there is
probably some in Wisconsin, but I'm not sure that's what you have in your yard!
There is a cousin plant, Oak-leaved Goosefoot, (Chenopodium glaucum L.)
which can have oblong leaves (also toothed or scalloped edges), and is another edible
weed naturalized from Europe.
So, yes there are several types!
Might be worth a closer examination to see what you really have.
BTW The Goosefoot Family includes not only these, but beets and spinach!