I have some bad news for you. You can not ever harvest celery seed from a lovage plant. Celery plants produce celery seeds and lovage plants produce lovage seeds.

The lovage plant is a green plant that sprouts in the spring of every year. Lovage is an herb use often in cooking to increase the flavor of a dish. Review of lovage in cooking dishes is good as well and it goes great with tomatoes.

Chuchupate, Indian parsley, Porter's lovage, mountain lovage, Colorado cough root.

Lovage-, Levisticum officinale, is a perennial herb that looks like parsley and is in the parsley, or Apiaceae, family, like anise, dill, caraway, cumin, and fennel. Lovage is native to mountainous areas of southern Europe and Asia Minor. It is sometimes called sea parsley.

answer is lovage.