A Bit of Seedling Botany

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Sunflower seedlings, each showing 2 cotyledons (seed leaves) still not fully deployed.

We probably all learned some elements of botany in school… but no one’s memory is perfect and there are often elements of our knowledge that may have become somewhat vague over time. That’s why it never hurts for gardeners to do a quick review of a few elements of botany from time to time. And here is one, about those first leaves you see when your start plants from seed: cotyledons.

Flowering Plants

Flowering plants can be divided into two main classes, monocots (monocotyledons) and dicots (dicotyledons). Their name comes from the number of cotyledons (seed leaves) which appear when they germinate.

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Monocots produce only one cotyledon… and it generally resembles the adult leaves.

Monocots produce only one cotyledon and generally it has a form similar to that of the adult leaf. For example, when corn and onions, two well-known monocots, geminate, their first leaves resemble those they’ll produce for the rest of their lives.

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Dicots have 2 cotyledons.

Dicots produce, as the name suggests, two cotyledons… and they almost never resemble the plant’s mature leaves. In general, cotyledons are simple and entire whereas the plant’s mature leaves can come in a wide variety of shapes and are often lobed or cut. Roses, cosmos, tomatoes, and most other plants with showy flowers are dicots.

And conifers?

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Seeds of conifers often have many cotyledons.

So much for flowering plants or angiosperms. But what about gymnosperms, a group that includes conifers (pines, spruce, larches, etc.)? Typically they produce a multitude of cotyledons, as few as 2 and as many as 24, but most often 10 or 12. Their cotyledons often look very similar to their mature leaves.

Short-Lived

In general, when the seedling is well established and bears several true leaves, its cotyledons dry up or fall off, having no other role to play.

The Exceptions

The plant kingodom is very complex, so there are exceptions to all just every rule, including the ones about cotyledons. You’ll find there are higher plants whose seeds contain no cotyledons (most orchids), cotyledons than remain underground (oaks and some beans), dicots that have (at least apparently) only one cotyledon (some waterlilies), and other cotyledonous anomalies. Plus algae, mosses and ferns, which don’t bear seeds at all and therefore have no cotyledons either.

However, when you start seeds for your garden, in 99% of cases you’ll see 1, 2 or multiple cotyledons… and that will help you place them in the right category!20161117a

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