Persicaria Tinctoria (Polygonum Tinctorium) is one of the most simple plants I've ever encountered in terms of propagation from leaf cuttings. Simply trim a stem with five or six leaves, plop it in water, and let time be your tool! No rooting hormones or fertilizers are necessary. Adventitious roots will emerge at the base of each stem node that is submerged in water! This begins to happen within a matter of hours. I've had success with transplanting these newly rooted indigo clones back into the soil after one week.
I've been keeping my clippings in a cup full of water on a sunny window sill.
I've pulled out a few different clippings from the water and placed them on a dark background to highlight the speed and location of the root growth.
This is a fresh indigo clipping with five formed leaves. The cut was made between nodes. No rooting has occurred.
On the third day, rooting is evident from the base of the lowest node. The roots from the next node up on the stem are just beginning to emerge.
By the fifth day, the roots can be an inch or more in length and are reaching out from every node that is submerged beneath the surface of the water the plants are stored in.