What does cotyledon mean?
A cotyledon is the first leaf — or pair of leaves — formed in the embryo of a seed-bearing plant, commonly called a seed leaf. It emerges during germination and typically either stores nutrients absorbed from the seed or begins photosynthesis while the seedling's true leaves develop. The number of cotyledons is a fundamental classification tool in botany: flowering plants with one cotyledon are known as monocotyledons (monocots), including grasses, lilies, and palms, while those with two are dicotyledons (dicots), such as beans, roses, and oaks. The word is used mainly in scientific, horticultural, and educational contexts rather than casual conversation, and its plural is simply cotyledons. Medicine borrows the term for the lobed divisions of the placenta, though this sense is rarer. Understanding cotyledons helps explain how seeds fuel their own early growth, making the word essential reading for students of botany and curious gardeners alike.
nounA cotyledon is the seed leaf of a plant embryo, the first leaf or pair of leaves to emerge during germination, which often stores or absorbs nutrients for the developing seedling.
- A seed leaf: the primary leaf or leaves in the embryo of a seed plant, which may store food or absorb nutrients during germination.
- (Botany, historical/anatomical use) A lobe or fleshy division of certain organs, as in the cotyledons of the human placenta.
"The bean seedling pushed a single cotyledon above the soil before its true leaves unfurled."
"Monocots such as grasses produce a single cotyledon, while beans and other dicots produce two."
"The placenta is divided into distinct cotyledons, each served by its own branch of the umbilical vessels."
Standard English plural; used when referring to both seed leaves of a dicot embryo or to multiple embryos' cotyledons.
"Dicotyledonous seeds contain two cotyledons, which swell as they absorb water during germination."
Count a seed's cotyledons and botanists can tell you which great family it belongs to — one makes it a monocot, two makes it a dicot.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of cotyledon
The word cotyledon derives from the Greek kotylēdōn, meaning a cup-shaped hollow or cavity, itself formed from kotylē, a cup or bowl. Ancient writers applied the term to cup-like structures, and early modern botanists adopted it in Latin form for the seed leaf because of its rounded, cup-like shape in many plants. The word entered English around the early seventeenth century, initially in anatomical descriptions of the placenta before becoming established in botany. Its Greek root also lies behind related botanical terms such as cotyledonous, describing plants characterized by their number of seed leaves.
How cotyledon is actually used
Cotyledon belongs chiefly to botanical and scientific register; it appears in gardening guides, textbooks, and exam biology rather than everyday speech. In casual contexts, gardeners often say 'seed leaf' instead. The plural 'cotyledons' is standard. The term also has a technical anatomical sense for the lobes of the placenta, though this is far less common outside medical writing.
Easily confused with cotyledon
A cotyledon is a seed leaf of an embryo, whereas a coleoptile is the protective sheath enclosing the emerging shoot in grasses such as maize and wheat.