a small hard object produced by plants, from which a new plant of the same kind grows.——朗文当代大辞典

As a count noun: the typically small, roundish structure by which certain higher plants reproduce and disperse themselves, which develops from a fertilized ovule and consists of an embryo plant and (often) nutritive endosperm enclosed in a protective coat. Also: the spore of a lower plant or fungus; a small hard fruit resembling a seed.——牛津当代大辞典  @en