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Introduction
Monocotyledonous plants have narrow, elongated leaves with parallel venation, which is used to distinguish them from dicots.
Monocot leaves are isobilateral because the colour on both surfaces of the leaves is the same.
A proximal leaf base, or hypophyll, and a distal leaf hyperphyll make up the primordial monocot leaves.
In dicots, the hyperphyll is the major structure of the leaf, but in monocots, the hypophyll is the dominant structure.
The leaves are slender and linear, with a sheath enveloping the stem at the base, however monocots contain several exceptions that do not have similar features.
Monocots leafs structure :
Bulliform cell
Bulliform cells in the top epidermis are not found in every monocot. This is an adaptation found in many grasses that thrive in hot or dry conditions.
The bulliform cells can contract to prevent water loss, causing the leaf to roll up and minimise surface area.
A leaf from the beach grass Ammophila has rolled in on itself in the photograph below.
Vascular bundles
The xylem will be on top (adaxial side) and the phloem will be on the bottom of the vascular bundle (abaxial side).
When you consider how a leaf emerges from the plant, you’ll see that the xylem and phloem in the stem are oriented differently, with the xylem closer to the centre and the phloem closer to the outside/epidermis.
A bundle sheath is a structure formed by inflated parenchyma cells that surround the vascular bundle. This is where the Calvin Cycle occurs in C4 plants, such as corn.
Leaf ventilation
Leaf venation is striate, most commonly arcuate-striate or longitudinally striate (parallel), less frequently palmate-striate or pinnate-striate, with leaf veins emerging at the leaf base and then running together at the apices.
Because the leaf base covers more than half of the circumference, each node normally only has one leaf.
Rather than meristem activity, developmental variations in early zonal differentiation have been blamed for the emergence of this monocot trait (leaf base theory).
Vascular System
Monocots have an atactostele, which is a vascular tissue architecture in which the tissue is distributed rather than grouped in concentric rings.
Monocot stems, roots, and leaves lack collenchyma. Many monocots are herbaceous and lack the vascular cambium seen in non-monocot woody plants, which allows them to increase the width of their stems (secondary growth).
However, some monocots do have secondary growth, which is referred to as “anomalous secondary growth” since it does not result from a single vascular cambium produces xylem inwards and phloem outwards.
Palms (Arecaceae), screwpine (Pandanaceae), bananas (Musaceae), Yucca, Aloe, Dracaena, and Cordyline are examples of giant monocots that either exhibit secondary growth or can reach huge sizes without it.
Monocot Apomorphies
Herbaceous habit, leaves with parallel venation and sheathed base, a single cotyledon embryo, an atactostele, numerous adventitious roots, sympodial growth, and trimerous (3 parts per whorl) flowers with 3 sepals, 3 petals, 2 whorls of 3 stamens each, and 3 carpels are among the monocot apomorphies (characteristics derived during radiation rather than inherited from an ancestral form).
Monosulcate pollen, on the other hand, is regarded as a plesiomorphic ancestral feature.
Conclusion
Monocotyledonous plants have narrow, elongated leaves with parallel venation, which is used to distinguish them from dicots.
There are over 60,000 species of monocotyledons. The orchids (family Orchidaceae) are the largest family in this group (and in flowering plants in general) by number of species, with over 20,000 species.
Monocotyledons produce the majority of the biomass produced in agriculture. Not just major crops like rice, wheat, and maize are included.
