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

https://upload.wikimedia.org/wikipedia/commons/b/b0/Dicot_leaf_L.jpg

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)

https://sites.google.com/site/botany315/plants-structure/6---shoots-pt-2-leaves/Zea%20leaf.jpg?attredirects=0

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"

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