Magnolias and daisies. About 200 families of flowering plants (Class: Dicotyledons or Magnoliopsida) have been recorded in Mexico, comprising around 18,000 species (Villaseñor, 2004). A sample of 30 families is presented, selected either for their diversity in Mexico, for being restricted to Mexico, or for their uniqueness.
They are called dicotyledons because in their early stages of development they have two cotyledons. These form a very important part of the plant embryo, and become the first leaves of the seedling. The cotyledons contain accumulated reserves of proteins, fats and sugars that enable the rapid growth of seedlings. The main differences with the other group of flowering plants (monocotyledons or Liliopsida) are:
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The veins of the leaves form a network, unlike the parallel venation of the monotocots. |
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They normally have 4 or 5 sepals and petals, instead of three as in the monocots. |
| Conducting tissues (xylem and phloem) are arranged in the form of a ring. |
| They have two or more cotyledons in the embryos |
| They undergo secondary growth, i.e., they thicken and form wood. |
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