Reddit reviews Botany for the Artist: An Inspirational Guide to Drawing Plants

So, I think the issue is in your rendering; your value range on the leaves is shorter and less organized than on the bird. The forms looks really good actually, the shapes on those flowers are quire sensitive. But one of the tricks with leaves is that even though they often 'reduce' in the eye to a lot of random shapes, they need to be just as carefully rendered as everything else. Just go slow and remember to add darks, respect highlights and pay attention.

If you want to kickstart your nature drawings, I suggest Sarah Simblet. Her book 'Botany for the Artist' is invaluable.

I'll second James Gurney's books, his blog and his "In the Wild" video series.

I really like the Complete Guide to Drawing Animals by Gottfried Bammes. It brought together a lot of concepts about anatomy in art that I hadn't really fully understood until I read it. Similarly, I think Sarah Simblet's Botany for the Artist has beautiful and inspiring art.

I'm a big old paleontology nerd, so I have a lot of books on my shelves with fantastic paleoart: Dinosaur Art, edited by Steve White, is a great showcase of modern paleoartists, and Feathered Dinosaurs is full of gorgeous paintings by Peter Schouten. For drawings of dinosaurs of the non-extinct variety, I'm fond of Katrina van Grouw's The Unfeathered Bird.

And I just got a copy of Shaun Tan's The Bird King and, oh man, I really love it. His imagination is incredible. Highly recommended for when you're in a creative rut.