Looking for new leaves to knit, I found the triangular leaf of the Mile-a-minute plant (Persicaria perfoliata). It’s native to India and Eastern Asia. The knitted leaf starts at the point and works toward the stem end, so you can determine how big your leaf will be. An I-cord stem is optional.
The pictured leaf is life-size: 3” by 3.5” without the stem. DMC #5 perle cotton color 907 was used.

Skills needed: cast on, knit, purl, knit front and back of 1 stitch and bind off in knit stitch.
Optional: I-cord for stem

Gauge is not important in this pattern. Any block-able yarn/thread will work. Make a swatch to check gauge and appearance.

11 yards of #5 pearl thread will make a 3” by 3.5” leaf with a 3” stem in the stated gauge.
One 27-yard DMC skein will make 2 leaves at gauge.