Orange seeds, like those of all citrus fruits, are the reproductive units of the plant. Their primary function is to protect the embryonic plant and provide the necessary nutrient reserves for germination. While all orange seeds share a basic structure, their exact size, shape, and internal characteristics vary depending on the specific cultivar.
Physical Description of the Outer Seed
The exterior of an orange seed is defined by a hard, protective casing known as the seed coat or testa. A typical orange seed has an elongated, somewhat irregular shape, often described as an oval or teardrop, tapering slightly at one end. For common varieties like the Late Valencia orange, the seed is relatively plump, measuring approximately 14.66 millimeters in length. The surface of the seed coat is generally a pale cream or tan color when fully dried. This outer layer is a tough, durable barrier designed to protect the delicate structures within until conditions are right for sprouting.
Inside the Seed: Structure and Embryos
Beneath the tough outer hull, the orange seed is primarily composed of two large, fleshy cotyledons. These cotyledons function as the plant’s main food storage organs, accumulating nutrient reserves during development. Orange seeds are classified as ex-albuminous, meaning the endosperm—a common food storage tissue—is absorbed by the developing embryo before the seed matures.
A key biological trait in many orange seeds, such as Valencia varieties, is polyembryony. This means a single seed can contain multiple embryos. These embryos arise from two distinct sources: the zygotic embryo, resulting from sexual reproduction, and several nucellar embryos, which are asexual clones derived from the maternal tissue. A single seedy orange may contain an average of three to five embryos.
Seed Differences Across Common Orange Varieties
The appearance of orange seeds is influenced by the specific variety and its reproductive mechanism. Many oranges found in grocery stores, such as the Navel orange, are virtually seedless due to a natural process called parthenocarpy. This allows the fruit to develop without the ovules being fertilized, resulting in no seeds or only vestigial, undeveloped structures.
In contrast, varieties like the Valencia orange or certain heirloom types are typically polyembryonic and contain a noticeable number of fully developed, viable seeds. The absence of seeds in varieties like the Navel orange is a desirable mutation that must be maintained through grafting, as the seedless trait prevents natural sexual propagation.