I really love ferns, and it's been on my bucket list of specimens to paint for a long time.  I actually finally completed two of them this spring!  Although I think they're so fascinating, getting into painting one really was quite a challenge, seriously SO MUCH GREEN!  I love the design in them, the whole big leaf is really duplicated smaller and smaller on each leaf stem as you look closely.  Then there's the fiddle heads' sweet little curls, oh so intricate, AND SO GREEN!  

Painting it really became a study in value.  This is something I learned about in a pastel class of all places years ago, but when I started to understand values, looking at your subject in grey tones to see light and dark shades, it was like a light bulb moment.  I tell my students to look through a piece of red acetate, or take a photo and convert to black and white to check if you're going dark enough with your colors for contrast.  Once you can see and adjust that, your painting almost paints itself, whether your working with many many colors, or mostly just one.