As part of its efforts to source its materials more responsibly, LEGO is launching a line of plant forms made from sustainable sugarcane plastics instead of petroleum-based plastic.
Note that these polyethylene pieces are not biodegradable, but they are sustainable. Via their announcement:
The new sustainable LEGO elements are made from polyethylene, which is a soft, durable and flexible plastic, and while they are based on sugar-cane material, they are technically identical to those produced using conventional plastic. The elements have been tested to ensure the plant-based plastic meets the high standards for quality and safety that the LEGO Group has, and consumers expect from LEGO products.
• LEGO Plants Now Made from Real Plants (YouTube / LEGO Group)