I only used few brushes when I painted landscape paintings both in oils and acrylics. I am a self-taught artist and no one taught me to used specific brushes for a specific medium. Sometimes I used watercolor brushes in acrylic painting and still works for me and even in oil but not too often. I am not also picky when it comes with brands and prices. Cheap or expensive it's all the same for me. As long as I am comfortable and it works. Below are the most common brushes I used in my paintings, acrylic, oil or watercolor, I just choose which one will fit on my needs.
Brushes for smaller details:
When it comes to details like small branches, single leaves, hair strands, detailed grasses and other circumstances that need to use a smaller pointed brush. These are the types of brushes I played with.
Flat Brushes for bigger details and textures:
I used this group of brushes for painting the whole area like the entire sky. These brushes are good for painting the details of the forest leaves or tree leaves. It can also be use for the bushes, grasses and vegetations.
Whatever brush you are using as long as you are comfortable and it can give the results you want, I must say that you are using the right kind of brush. I can even use a pointed smaller brush to do the leaves of the forest but it takes more time and the results will still almost the same and more detailed. The most important thing is to practice using your brush. The more experience you have the better results you can achieve.
When I started painting 16 years ago, I practiced on my own and everyday I discovered something new. Some technique that give me good results. I keep painting almost everyday and got to know my brushes. How I should hold it and the right pressure on the canvas' surface and many more. I keep learning until I became better than yesterdays.
My few brushes:
Oil Portrait Paintings, Landscape Oil/Acrylic, Abstract and directly copy from picture. Best for birthday gifts, anniversaries, weddings and even for personal collections.