No, biomass energy doesn't only come from plants. While plant matter is a common source, biomass energy can also be derived from:

* Animal waste: This includes manure and other animal byproducts.

* Wood waste: This can include sawdust, wood chips, and other wood scraps from forestry and construction.

* Agricultural waste: This includes crop residues, such as corn stalks and rice husks, as well as food waste.

* Municipal solid waste: This includes garbage, paper, and other household waste.

* Algae: This rapidly growing organism can be used to produce biofuels.

Essentially, any organic material can be used for biomass energy, though some sources are more efficient and sustainable than others.