Radial Parenchyma
Radial Wood Sections
Rainbow Funnel of Humic Acids
Rams Horns
Ray Initials
Ray Shakes
Reaction Wood
Reaction Zone
Recycle
Red Heart
Redox Potential
Reduction and Oxidation
Regenerating and Generating Systems
Religion
Renewable Resource
Reproduction
Research
Researchers
Resin Ducts
Respiration
Respiration and Photosynthesis
Rest
Rhizomorphs 
Rhizoplane
Rhizosphere
Rib Wood
Ring Porous
Ring Shakes
Roads or Forest
Robert Hartig
Robots
Rocks
Root
Root / Aerial
Root Collar
Root Exudates
Root Flair or Flare (sic?)
Root Growing
Root Hairs
Root Hairs / Mycorrhizae
Root Plasmolysis
Root Pruning
Root Rots
Root / Seed
Root Sprouts
Root Stubs (Woody)
Roots
Roots / Seed
Rot, So Blatantly Called
Rots
Rotten
Rotten Wood
Rubber / Natural