Which term describes a seed plant having a single cotyledon?

The term that describes a seed plant having a single cotyledon is "monocotyledon." In botany, monocots are characterized by their seed structure, which features one cotyledon or seed leaf. This differentiates them from dicotyledons, which have two cotyledons. Monocots typically include plants like grasses, lilies, and orchids. They exhibit distinct features such as parallel leaf venation, flower parts usually in multiples of three, and a fibrous root system. Understanding these characteristics is fundamental in plant identification and classification.

Other terms such as dicotyledon refer specifically to plants with two cotyledons and do not apply here since they do not share the single cotyledon trait. Gymnosperms are a broader category that includes seed-producing plants that do not form flowers or fruits, while angiosperms refer to flowering plants, which can be either monocots or dicots. Therefore, "monocotyledon" is the precise term that relates to seed plants with a single cotyledon.