"Plant matter" refers to any substance that comes from a plant, such as leaves, stems, roots, or flowers. It basically means anything that is part of a plant. Full definition
They can even be combined with the burning of plant matter to create a «carbon negative» fuel that when burned removes more CO2 from the air than it puts in. (scientificamerican.com)
A poor diet inhibits digestion, causing waste and partially digested plant matter to «build up» inside the body. (petconsider.com)
The new analysis concludes that trees and other plant matter took up one third to two thirds of a billion tons of carbon each year between 1980 and 1989. (scientificamerican.com)