Dicots

Dicotyledonous plants—commonly referred to as dicots—are a diverse group of flowering plants (angiosperms) recognised for a significant number of essential characteristics. One of the major differences is that dicots have two cotyledons (embryonic leaves) within their seeds, distinguishing them from monocots, which have one. The plants commonly called dicots are incredibly diverse, including tiny herbs to large trees.

1.0Introduction

The term “dicot” is derived from the Greek words “di” (two) and “cotyledon” (seed leaf). It literally means “plants having two seed leaves.”

2.0Definition

Dicots (or dicotyledons) are flowering plants (angiosperms) containing seeds with two embryonic cotyledons. They typically display net-like venation in the leaves, a taproot system, and vascular bundles arranged in a ring.

3.0Dicot Characteristics

The following features are classic indicators of a dicot plant:

1. Seed Structure: This is the cotyledons, which store food for the developing embryo. A dicot seed will contain two cotyledons, which store food for the growing embryo. Examples would be beans, peas, and peanuts. Examples include beans, peas, and peanuts. 
2. Root System: Dicots usually exhibit a taproot, which is a firm, single root that grows deep in the soil from the single main root and takes on many lateral roots. A taproot system provides firm anchorage and good water uptake.
3. Leaf Venation: The leaves on dicots typically exhibit reticulate or branched venation, or a net-like pattern for the arrangement of the leaf's veins. A monocot would show a separate pattern of parallel venation.
4. Stem Anatomy: Dicot stems have their vascular bundles arranged in a distinctive pattern in a ring, located within the pith. This ring pattern is necessary in stems for secondary growth, which is an increase in the girth or thickness of the stem. The vascular cambium between the xylem and phloem in dicots enables secondary growth and is visible as the outer bark of most trees. Most trees are dicots. 
5. Flower Parts: The floral parts (petals, sepals, etc.) in dicot flowers are usually arranged in multiples of four or five. Think of a rose with its numerous petals or an apple blossom with five petals. 
6. Pollen: Dicot pollen grains typically have three furrows or pores (tricolpate), unlike monocot pollen, which has a single furrow or pore.

4.0Anatomy of Dicot Plants

1. Dicot Root: The anatomy of a dicot root, when viewed in a transverse section, reveals several distinct layers:

• Epidermis: The outermost protective layer with unicellular root hairs for water and mineral absorption.
• Cortex: A multi-layered region of parenchyma cells for food storage and water transport. The innermost layer of the cortex is the endodermis, which contains Casparian strips that regulate water flow into the vascular cylinder.
• Pericycle: Located just inside the endodermis, this layer gives rise to lateral roots and a portion of the vascular cambium during secondary growth.
• Vascular Bundles: The xylem and phloem are arranged in a radial pattern. The xylem is typically star-shaped with phloem bundles located between its arms. The central pith is small or absent.

2. Dicot Stem: A young dicot stem in a transverse section shows a well-defined arrangement of tissues:

• Epidermis: The outermost protective layer covered by a cuticle.
• Cortex: Differentiated into three sub-zones: a collenchymatous hypodermis for mechanical support, a general cortex of parenchyma, and an innermost endodermis (starch sheath).
• Vascular Bundles: Arranged in a ring. Each bundle is open due to the presence of a vascular cambium between the xylem and phloem, which enables secondary growth.
• Pith: A large, central region of parenchyma cells for storage.

3. Dicot Leaf (Dorsiventral Leaf): The anatomy of a dicot leaf is adapted for maximising photosynthesis:

• Epidermis: The leaf is covered by an upper (adaxial) and lower (abaxial) epidermis, with the lower surface generally having more stomata.
• Mesophyll: The ground tissue between the two epidermal layers is differentiated into two types of parenchyma:
• • Palisade parenchyma: Elongated, tightly packed cells rich in chloroplasts, located just below the upper epidermis.
  • Spongy parenchyma: Loosely arranged, irregular cells with large air spaces, located below the palisade layer. These spaces facilitate gas exchange.
• Vascular Bundles: Found within the veins and midrib, they are surrounded by bundle sheath cells. The xylem is on the upper side, and the phloem is on the lower side. The prominent veins correspond to the reticulate venation seen on the leaf surface.

5.0Examples of Dicots

Common examples of dicot plants include:

• Legumes: Pea, bean, gram, lentil
• Fruits: Mango, guava, apple, orange
• Flowers: Rose, hibiscus, sunflower, marigold
• Trees: Banyan, neem, teak, mango tree

Dicots are widespread across families like Fabaceae, Asteraceae, Solanaceae, and Rosaceae.