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. 

• No. 1 Flat Brush - I used these brush for single leaves or detailed kind of leaves which are nearer to the viewers eye. I also used this for bigger branches and twigs. 
• No. 0 Round Brush - These are the smallest brush on the group. I used this one for the smallest detailed like the smaller branches and details on the trunks. I also used this one for the taller and thinner grasses. These brush is also best for hair strands and signature.
• No. 2 Flat Brush - The same function on No. 1 Flat brush.
• No. 12 Round Brush - These brush can replace all of the above brushes. These can be so pointed that it can create small details like the smaller brushes and also can be use in signature but only if you have good control on this brush.

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. 

• 1-inch Flat Brush - Even though old and the bristle toe is almost worn out. It has the best result when it comes to painting the textures of leaves and grasses compare to the new ones. So don't throw your old flat brush because it has the best bristle for painting tree leaves. This is also good for painting the large area like the entire sky.
• No. 6 Flat Brush - This brush is good for painting the details on clouds. It has medium size and easy to use. This one also good for the detailed far mountains. This can also be use in painting tree leaves.
• No. 4 Flat Brush - This brush has almost the same function on No. 6 but more detailed and smaller.  

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: