One artist who took such care was Peder Mork Mønsted (Danish 1859-1941). In his long career he painted landscapes of all sorts, and managed to blend painterly handling with conscientious rendering.
In this foreground detail of the painting above, he observes the character and the color of each leaf, and records how the colors change as the leaves move in and out of shadow.
But a forest is more than the sum of its leaves, or even of its trees. Mønsted improvises a different toolset for the far masses of foliage, generalizing and softening where he needs to.
Improvisation and resourcefulness is vital to painting foliage. The tools and methods that we learn from painting casts or figures in the academy don't really serve us outdoors as we face the changefulness and immateriality of nature.
As we've seen in this series, complete imitation of every leaf in a lush landscape is probably not possible or even desirable, nor perhaps is the other extreme of ultra-softness and generalization. One can be faithful to the character of the plant without copying or imitating every detail. Instead, nature must be re-created or "represented" in paint on the canvas.
Asher B. Durand, in his influential 1855 essays "Letters on Landscape Painting" draws this very distinction between imitation and representation. When painting a tree, he says, “direct imitation is impossible." Instead the artist should strive to “represent this foliage in every essential characteristic, without defining the forms of individual leaves. To do this, some analysis of its structure is necessary.”
There's more to say about structure, but I'll save that for future posts.
More on Mønsted on Lines and Colors
Full text of Letters on Landscape Painting in The American Landscapes of Asher B. Durand
The Artistic Anatomy of Trees (Dover Art Instruction)
More on leaves and foliage in my book Color and Light, which you can get signed here.
Part 1: Painting Tools