Monocots vs. Eudicots
Angiosperms are a very diverse group, and in education there are two groups traditionally used to represent this diversity. Monocots represent ~20% of angiosperm diversity, and eudicots represent ~66% of diversity. By studying these two groups, students can observe the general anatomical & morphological diversity of flowering plants.
*"Dicots" are now referred to as Eudicots, although the "dicot" features described below pertain to many non-monocot plants (e.g. many magnoliids)
Roots
How do their root morphologies differ?
Eudicots and monocots have differing root morphologies: tap roots and fibrous root systems, respectively
Tap roots
Hierarchy to root system: main root branches to create smaller side roots
Found in eudicots small (e.g. beans) and large (e.g. oaks)
Fibrous roots
All roots are equal-sized and emerge from stem
Limited or minimal branching of roots
Found in all monocots, whether small (e.g. grass) or large (e.g. palms)
Above (left) : tap root system, usually found in dicots. Above (right): fibrous root system, usually found in monocots
How do their root anatomies differ?
Eudicots and monocots have differing root anatomies: protosteles and eusteles, respectively
Protostele
Eudicots have a protostele pattern in their roots: xylem is located at the center of the root
The xylem in an X-shaped or star-shaped fashion; this is a specific type of protostele called an actinostele
There are pockets of phloem between the lobes of the X-shaped xylem
Eustele
Monocots have a eustele pattern in their roots: pith (with parenchyma cells) occupies the center of the root
The xylem forms a ring-like pattern around the pith
There are pockets of phloem outside of the ring of the xylem
Above (left): Cross-section of a eudicot root. Notice the central position of the vascular tissue in a cross-like configuration. Above (right): Cross-section of a monocot root. Notice the ring-like appearance of the vascular tissue.
Stems
How do their stem morphologies differ?
Eudicots and monocots have differing stem morphologies
Eudicots
Hierarchy to shoot system: main trunk branches to create... branches, which give rise to twigs
Found in eudicots small (e.g. beans) and large (e.g. oaks)
Monocots
Generally, upright shoots tend to be similar in size and vigor, but some branching does occur in monocots
Found in all monocots, whether small (e.g. grass) or large (e.g. bamboo)
How do their stem anatomies differ?
Eudicots and monocots have differing root anatomies: eusteles and atactosteles, respectively
Eustele
Eudicots have a eustele pattern in their stems: pith (with parenchyma cells) occupies the center of the stem
The xylem forms a ring-like pattern around the pith
There are pockets of phloem outside of the ring of xylem
Atactostele
Monocots have an atactostele pattern in their stems: xylem and phloem are arrange in bundles that are scattered throughout the cortex of the stem
Above (left): Monocot stem in cross-section. Notice the scattered appearance of the bundles. Above (right): Eudicot stem cross-section. Notice the ring-like appearance of the vascular tissue.
Stem vs. Root anatomy synopsis
The eudicots have eustele pattern in their stems, but a protostele pattern in their roots
The monocots have an atactostele pattern in their stems, and a eustele pattern in their roots
Are you confused yet?
Leaves
How do their leaf morphologies differ?
Eudicots and monocots have differing leaf morphologies, most notably in the veins of the leaf
Eudicots
Veins are usually netted/branched in eudicots
Monocot
Veins tend to be parallel to each other
How do their leaf anatomies differ?
Eudicot and monocots have differing leaf anatomies
Eudicots
Epidermis
One cell layer surrounding the leaf that serves as protection of leaf tissues
Coated with cuticle, waxes, and hairs
Mesophyll
Parenchyma cells specialized for photosynthesis
Palisade layer
Site of energy-capture;
Contains 80% of plant’s chloroplasts
Composed of chlorenchyma tissues
Spongy layer
Site of gas and water exchange
Composed of aerenchyma tissue
Stomata
Guard cells regulate gas and water exchange; usually on lower surface
Above: Cross-section of eudicot leaf
Monocots
Mesophyll
Less defined than eudicots
Mesophyll uniform; not differentiated into palisade and spongy layers
Bulliform cells
Function to roll leaf blade
May reduce transpiration
Veins
Many monocots, like C4 grasses, will have a bundle sheath around the vascular tissue
Stomata
Found on the epidermis of both surfaces (abaxial and adaxial)
Above: Cross-section of monocot leaf. Notice the bubble-like bundle sheath cells around each veins
Flowers
How do their flower morphologies differ?
Eudicot Flower
Flower parts in multiples of 4s or 5s
This includes sepals, petals, and stamens
Monocot flowers
Flower parts in multiples of 3s
This includes sepals, petals, and stamens
Above (left): cross-section of a monocot flower. Notice the parts in multiples of 3s; Above (right): cross-section of a eudicot flower. Notice the parts in multiples of 5s
Seedlings
How do their seedling morphologies differ?
Eudicot seedlings
Eudicots have seedlings with two (2) cotyledons or seed leaves
The name "dicot", means "2 cotyledons"
Monocot seedlings
Monocots have seedlings with one (1) cotyledon or seed leaf
The name "monocot" means "1 cotyledon"
