Before we start studying eudicotyledons we need to remember some concepts.
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- Why use eudicots and not dicots?
- Do you know what a cotyledon is?
- Growth in thickness of eudicotyledons
- Differences between monocots and eudicots
Why use eudicots and not dicots?
In the past, angiosperms were divided into monocots and dicots . However, after molecular phylogenetic studies, it was found that not all plants classified as dicots were monophyletic, that is, not all had the same common ancestor.
Therefore, they were divided into two groups: the eudicotyledons (the prefix “eu-” means “true”), from the Eudicotyledoneae clade and the magnoliids, basal plants of the Magnoliids clade that do not fit neither in monocots nor in eudicots.
Magnoliids have more primitive characteristics, they include species such as laurel, peppers and magnolias.
Therefore, currently the correct terms suggested by the Angiosperm Phylogeny Group (APG) for the classification of angiosperms are: monocotyledons, eudicotyledons and magnoliids.
Do you know what a cotyledon is?
The cotyledons are leaves early days of an embryo. They can perform various functions such as: reserve, photosynthetic organ and also water and nutrient absorption.
It is the cotyledons that nourish the new plant until the formation of the first true leaves, later they are reabsorbed, serving as a source of nutrients .
Thus, we have plants that have only one cotyledon, called monocots, and those that have two cotyledons, called eudicots.
Eudicotyledons, also known as “eudicots”, are a monophyletic group where individuals have two cotyledons in the embryo .
This is the largest group of angiosperms, consequently, it is also the one with the greatest morphological and anatomical diversity.
In most eudicotyledons, cotyledons are large, fleshy and store nutrients that will be used for energy during germination. This is because most of the endosperm reserves are absorbed by cotyledons during embryo development.
However, there are exceptions that have developed endosperm, for example, castor beans. In this case, the cotyledons are membranous and delicate and will only absorb the reserves of the endosperm during the growth of the embryo.
In addition to the two cotyledons, see some basic characteristics for eudicotyledons :
- They may show secondary growth;
- The ribs have a diversified pattern, usually branched, of the peninerval type;
- The floral elements are in multiples of four or five, often pentamerous;
- The vascular bundles are distributed in a ring shape;
- The roots are pivoting, that is, it has a main root and other secondary ones derived from it;
- Pollen grains are of the type tricolpado or derived from it.
Are examples of eudicotyledons : beans, mango, daisy, sunflower, soy, rose bushes, strawberry, pumpkin, cucumber, tomato, eggplant, peppers, among many other plants.
Growth in thickness of eudicotyledons
The eudicotyledons can have secondary growth through the phellogen and the vascular exchange, the meristems responsible for the formation of the periderm and the secondary xylem and phloem, respectively.
The activity of these secondary meristems is that it increases the number of cells causing the organs, stems and roots to grow in thickness.