As I mentioned recently, the seed coat sometimes remains on a plant’s seed leaves or cotyledons, trapping them so that the young plant can’t grow properly. Soil or other material can similarly bind seedlings’ leaves.
If the seed coat or other problem doesn’t drop off on its own within a day or two, I try to remove it and separate the seed leaves. I wait a bit because it’s possible to injure the seedling. I first squeeze the seed coat to try to get it to pop apart. If that doesn’t work, I gently pull it off the plant.
This cilantro* ‘large leaf’ seedling’s leaves were already damaged and I couldn’t remove the seed coat cleanly. I think it’s better than if I’d left it, however.
In my experience, many dicotyledonous (having two seed leaves) plants can have their seed leaves stuck together like this. Here’s a tomato seedling with a similar problem.
This time, I could release the seed leaves without damage. This tomato is of the ‘Polish linguisa’ variety, which germinated a little later than the other varieties that I planted at the same time.
Now that I’ve removed the obstruction, the seed leaves or cotyledons can spread so they can more efficiently collect light and transform it into the chemical energy that the plant uses to grow.
Cotyledons or seed leaves are formed within the seed when it is produced by the parent plant. In some species, the cotyledons stay in the ground and provide stored energy that the seedling uses when it first begins to grow. The seeds of these plants are usually large.
In other plants, such as the vegetables shown here, the cotyledons emerge from the ground and provide the seedling’s initial energy through photosynthesis.
True leaves are formed after the new plant germinates and usually don’t look like the seed leaves. In the photo below, the napa cabbage ‘optiko’ seedlings each have two seed leaves (the smooth-edged, heart-shaped leaves) and two true leaves (with rough, slightly hairy edges). The true leaves will grow into the large cabbage leaves that we eat, but the seed leaves usually don’t get any bigger. Often, they will wither and possibly disappear.
I find that the seed leaves of vegetables within a family all look alike, much as the seeds within a family all look alike; thus, cabbage, radish, kale, and mustard greens all have similar seed leaves.
Speaking of kale, here is a kale ‘starbor’ seedling with three seed leaves!
This is the first time I’ve seen a tricotyledon, or seedling with three seed leaves, but apparently tricots are quite common. Some people think it gives the seedling an advantage while others think the opposite. I haven’t found any authoritative sources with information on tricotyledons, so I’ll try to watch this seedling and see if there is a notable difference between it and the others. It does seem to be just a little bigger and further developed than the other kale seedlings at this point.
Update: The “mutant” kale seedling did seem to grow a little faster initially, but it may have just germinated a little before the others. Later in the summer, that plant was not appreciably different from the others.
Further update: See another “mutant” from my garden in this post.
*In the USA, we refer to this plant as cilantro when we use the leaves as an herb, and as coriander when we use the seeds as a spice. I grow it for the leaves, since it’s easy to obtain the seeds but the fresh leaves are rare (and expensive) in the grocery store.