What Are Monocots & Diocots?
Monocotyledons and dicotyledons (monocots and dicots) were first given formal recognition by biologist John Ray in 1682 in his publication, "Methodus Plantarum Nova." The terms were assigned to the two major classes of flowering plants and continue to be used today. The distinctions between the two classes are far from infallible and many exceptions occur in plants that possess the characteristics of both classifications. Botanists often disagree on the proper taxonomy placement for these exceptions to accepted botanical rules. Does this Spark an idea?
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Seeds
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Monocots have one cotyledon or seed leaf. Most monocots have an endosperm present in the seed. The endosperm is the tissue that surrounds and provides nourishment to the embryo as it grows and emerges from the seed. Dicots have two cotyledons (seed leaves) and may or may not have endosperm. Embryos that do not have an endosperm, such as in pea and bean seeds, absorb their food storage tissues before becoming dormant and develop large, fleshy cotyledons instead.
Roots and Vascular Systems
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The primary root of the monocot does not grow deeply into the ground but instead develops a network of shallow fibrous or fleshy roots branching from it. In the dicot, the primary root is a large, deep and predominant taproot with a few small secondary roots branching from it. The stems of the monocot have scattered vascular bundles that carry water and nutrients from the soil, through the roots to the upper levels of the plant. In dicots, the vascular bundles are arranged solely around the perimeter of the stem.
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Leaves, Flowers and Pollen
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Monocot leaves are usually linear or oblong in shape with veins running parallel along the length of the foliage. Dicots feature broader-shaped leaves with veins running in a net shape along the leaf surface. Monocot flower parts occur in threes or multiples of three. Dicot flowers commonly feature four or five parts. The pollen of the monocot has one furrow or pore, making it monocolpate. The dicot pollen is tricolpate, with three furrows or pores present. Monocots are usually herbaceous or leafy while dicots may be herbaceous or woody.
Exceptions
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Some plants have characteristics of both monocots and dicots but have been placed by botanists in one class or the other. The plants that seem not to fit entirely into one distinct class or the other are usually the result of a shared ancestry between monocots and dicots. Yams are monocots with the broad, veined leaves more characteristically found in dicots. Water lilies are dicots with a single, monocot-like cotyledon and scattered vascular bundles in their stems. No single characteristic, therefore, is sufficient in classifying a plant as a monocot or a dicot.
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References
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