School of Botanical Art & Illustration https://www.botanicgardens.org/education/school-botanical-art-illustration
Introduction to Botanical Illustration Start at the beginning. If you are puling from distant memory or drawing for the very first time, this gently paced course is for you. Through carefully explained demonstrations, simple exercises and helpful critiques, learn step-by-step observational drawing skills.
Watercolor 2 Bring what you learned in Watercolor Mixing and Watercolor Level 1 to create a finished painting from specimen observations in graphite, to complete a finished botanical plate. Learn to enhance perspective and depth, and gain confidence in the final detail. More techniques will be explored as you fix those at times, "mistakes".