This is the one and only origami creation I've come up with on my own...usually I just follow along in a book. However, I needed a good stem and couldn't find one, so I just got to folding, and this is what I came up with. There are many variations one could do on this basic approach. I show three, the last of which is shown in the main page photo.
Step 1: Required Materials
There is beauty in simplicity! All you need is one square sheet of paper, preferably green, I suppose - but you do whatever makes you happy. If the sheet is white on the back, then the backs of the leaves will be white also in the basic design. Note that the ultimate stem length will be the length of the paper diagonal, so you can either measure that or multiply the paper edge length by 1.4 if you want to get an idea of how big the end product will be.
Step 2: Valley Fold Along Diagonal
Try to keep the corners neat. If using traditional origami paper (which is colored only on one side), make sure to place the colored side up before performing the valley fold.
Step 3: Rabbit-ear the Top Layer
This fold is called a rabbit-ear, because it results in a flap that can be laid flat, just as a rabbit's ear can be pointed up or flopped back. Since you have just valley-folded the model, you now have two layers - this step is performed only to the top layer. The two valley folds coming up from the bottom corners exactly bisect the angle, so the diagonal edges will align perfectly with the bottom edge when the fold is complete. You can see that the third valley fold goes from where the two diagonal valley folds intersect to the top corner of the model. This will allow the formation of a point to the rabbit ear...if you fold this point either to the left or right, a mountain fold will form as well. See second image for this step to view the result of this fold.
Step 4: Flip and Repeat.
Flip the model over and repeat the rabbit-ear fold. This is how the model should look once you complete this step.
Step 5: Adding Pre-creases
Now fold the point of the top triangle down to the base in a symmetric fashion. The result will be a valley fold halfway from the top point and the base. Unfold.
Step 6: More Pre-creases...
Fold the top corner down to the pre-crease you just created in step 5. Unfold, then fold the pre-crease from step 5 down to line up with the lower edge of the paper. Unfold. The result should be three evenly-spaced creases along the front face of the model.
Step 7: Unfold Flap and Perform Sink Fold
Open up the rabbit-ear you created in steps 3 and 4. The result will be a set of 3 triangles of creases formed by the pre-creases completed in steps 5 and 6. Now comes the most difficult step: as shown in the image of the opened-up sheet by shading, reverse existing creases as necessary so that the outer triangle is all mountain folds, the middle triangle is all valleys, and the inner triangle is also mountains. Once the folds have been reversed to this pattern, you should be able to perform a "sink" fold that will flatten the triangle to lay flat against the other rabbit ear. This step is sort of like the paper fan we all folded as kids, except with triangles. The second and third images attached to this step show the sink fold halfway complete and essentially complete.
Step 8: Repeat Steps 5-7 on Opposite Flap
At this point, flip the model over and perform the same steps on the rabbit-ear you completed in step 4. Once complete, the model should look similar to the attached image when viewed from above.
Step 9: Rabbit-ear the Upper and Lower Stem
The stem is still a little too fat, so perform a long rabbit-ear down the lengths of the upper and lower halves of the stem. The diagonal folds of the rabbit-ear will be very short this time. This step results in a stem that is just about as thick in one direction as it is in the other - it also gives a nice natural appearance due to the multiple layers.
Step 10: Shape Leaves and Attach Flower
At this point, the stem is essentially complete. The leaves may tilted to different angles depending on the look you wish to achieve. For fuller leaves that are also smooth, open up just the outer layer of each leaf from the back, which will result in a rounded leaf appearance that has a stem line about halfway up the middle. For an even fuller leaf with a more natural appearance, open the middle layer of the leaf, again from the back, and press flat. Due to the geometry, the leaf will wrinkle a bit when you open the middle layer. Try to keep the folds down the middle crisp so as to give the appearance of a leaf stem. Reinforce the upper and lower stem folds to keep the stem narrow.
Usually a flower model will have a pocket or two into which you can slip the point of the stem. You can add another rabbit-ear or valley fold at the point to narrow the stem more for insertion into the pocket or to change the angle of the flower. The flower shown in the main photo for the instructable is from a book I had as a kid, called "The Complete Origami Course" by Paul Jackson. Not sure if it is still in print, but the idea is just to fold a waterbomb base in half to form four flaps, use a valley fold to put a crease near the line that formed the flaps, and then open up the flaps while flattening their bases.