Big Mac or McPlant, that will soon be the two options consumers in line at McDonalds (MCD ) will have for their latest high-calorie fast-food dinner.

The Golden Arches said Monday it has developed a plant-based patty it will dub the McPlant. A McDonalds spokesperson tells Yahoo Finance the McPlant will be put into test in 2021 on a market-by-market basis.

As we have worked to better understand customer demand, some markets around the world have tested plant-based products. Informed by those learnings, we have created a delicious burger that will be the first menu option in a plant-based platform we are calling McPlant. McPlant is crafted exclusively for McDonalds, by McDonalds, said McDonalds International President Ian Borden in a statement.

Borden continued, In the future, McPlant could extend across a line of plant-based products including burgers, chicken-substitutes and breakfast sandwiches. And, we expect some markets will test the burger next year. We are excited about the opportunity because we believe we have a proven, delicious-tasting product. When customers are ready for it, we are ready for them.

News of the McPlant sent Beyond Meat (BYND ) shares plunging nearly 10% in early morning trading Monday. Shares reversed losses in the afternoon as Beyond Meat came out in defense of its position. Beyond Meat and McDonalds co-created the plant-based patty which will be available as part of their McPlant platform, a Beyond Meat spokesperson told Yahoo Finance.

Beyond Meat shares have long reflected the expectation of a nationwide rollout with McDonalds. Getting into McDonalds has been a long-term goal of Beyond Meat founder Ethan Brown , per Yahoo Finances interviews with him this past year. So its easy to understand the markets initial reaction to McDonalds deciding to go it alone on the plant burger front.