Until recently, biologists divided flowering plants into two groups based on several characteristics, such as seed behavior, flower, stem and leaf appearance, and how their pollen and cells were composed. These groups were called monocots and dicots. However, today the dicot group has been divided into many subgroups, including the eudicots, sometimes called "true dicots," which comprise about 75 percent of all flowering plants. Although both groups belong to a family of plants called angiosperms, they have some notable differences, especially in regard to how their seeds germinate and function. These differences include the number of leaves within the seed, how the seed receives its first nutrients and how the first leaves look.
Number of Leaves
The greatest difference between monocots and eudicots is the number of leaves, or acotyledons, their seeds contain within its embryo. Monocot plants produce only one thin leaf when they germinate, hence their name. Eudicots, on the other hand, produce two leaves that sprout after germination.
The cotyledons of eudicot plants contain endosperm, a food source that the germinating seed depletes as it grows. Monocots, however, do not have endosperm inside their first leaves -- their endosperm is contained within the interior of the seed, and is absorbed through the leaves.
Due to the absorption of the endosperm, the first leaves of eudicot plants are fatter and rounder than the adult leaves. These leaves will drop off the plant as soon as the first set of adult leaves appear. The first leaf a monocot produces, however, is an adult leaf, usually long and thin. The plant will keep this leaf instead of allowing it to drop away.
There are no defining features unique to the outer appearance of both eudicot and monocot seeds, and the texture, size and shape of seeds belonging to both classes can differ greatly from species to species. In fact, seed shapes among monocots vary so greatly that this group of plants contains both the largest seed found on Earth, the Coco-de-mer, and the smallest, the Orchid.
The outer seed coating of a eudicot plant is made from two layers of integument, or tissue. Monocot seed coatings, however, are made from only one layer of integument. This means they are slightly thinner than those of the eudicot.
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