Here is the finished illustration for SESE of Rhubarb:
I added a lot of veins to the leaves first with a razor, scraping away some of the paper. Then I added a lot of shading in the stems and leaves with colored pencil, blending a bit with the white colored pencil. And lastly, I added some bluish shadow with watercolor again.
I looked for some more interesting things to write about rhubarb on wikipedia and I am just going to copy and paste a couple paragraphs here that I thought were fun. Who knew that rhubarb was once as expensive as opium and saffron?
For centuries the plant, [rhubarb], has grown wild along the banks of the River Volga, for which the ancient Scythian hydronym was Rhā. The expense of transportation across Asia caused rhubarb to be highly expensive in medieval Europe where it was several times the price of other valuable herbs and spices such as cinnamon, opium and saffron. The merchant explorer Marco Polo was therefore much interested to find the plant being grown and harvested in the mountains of Tangut province. A measure of the value set upon rhubarb can be gotten from Ruy Gonzáles de Clavijo's report of his embassy in 1403-05 to Timur in Samarkand: "The best of all merchandise coming to Samarkand was from China: especially silks, satins, musk, rubies, diamonds, pearls, and rhubarb...".
The term rhubarb is a combination of the Ancient Greek rha and barbarum; rha is a term that refers both to the plant and to the River Volga. Rhubarb first came to the United States in the 1820s, entering the country in Maine and Massachusetts and moving westwards with the European American settlers.