II. Monocotyledons and Dicotyledons

A. General information

1. The two classes of the division Anthophyta are monocotyledons and dicotyle-

dons, commonly referred to as monocots and dicots

2. Although the terms monocot and dicot refer specifically to the number of cotyle-

dons, or food storage organs, within the seeds of angiosperms, several other characteristics separate the two classes (see Comparison of Monocots and Di­cots, page 108)

B. Monocots

1. Monocots have only one cotyledon in each seed

a. The single cotyledon enzymatically absorbs food from the endosperm and

transports it to the growing embryo

b. The large cotyledon in the mature seeds of grass species is called the scutel-

lum

(1) The scutellum is attached to one side of the embryo, midway between

the plumule at the upper end of the embryo and the radicle at the

lower end (2.) The radicle, or embryonic root, is enclosed in a protective sheath

known as a coleorhiza (3) The plumule (epicotyl and young leaves) is enclosed within a protective

sheath called the coleoptile

c. The endosperm persists in the seed and is the primary source of stored food

for the embryo and young seedling during the early stages of germination

2. The flower parts (sepals, petals, stamen) usually occur in groups of three or multi-

ples of three

3. The leaves have parallel veins

4. Monocots tend to have fibrous root systems

5. The primary vascular bundles in stems are scattered throughout the cross section

Comparison of Monocots and Dicots
CHARACTERISTIC	MONOCOTS	DICOTS
Embryo	One cotyledon	Two cotyledons
Flower parts	Occur in groups of three	Occur in groups of four or five
Leaves	Parallel veined	Net veined
Roots	Many main roots (fibrous root system)	One mam root (taproot system)
Stem anatomy	Scattered vascular bundles	Vascular bundles arranged in rings
Root anatomy	Pith	Xylem in center
Secondary growth	No	Yes

6. The roots contain a central core of pith (parenchyma tissue derived from the pro-

cambium)

7. True secondary growth is rare or nonexistent because most monocots lack vascu-

lar cambium and cork cambium

8. Examples of monocots include cereal grains (such as corn, wheat, and oats),

sugarcane, lilies, daffodils, orchids, bananas, palms, and grasses

C. Dicots

1. Dicots have two cotyledons in each seed

a. The cotyledons are the food storage organs of the embryo

b. The endosperm does not remain unchanged in dicots; it is converted to a

cotyledon during seed development

2. The flower parts occur in multiples of four or five

3. The leaves have netlike veins

4. Dicots lend to have root systems consisting of a single main root (taproot) with

small branches

5. The primary vascular bundles in stems form a ring pattern

6. Most dicot roots, with the exception of those of a few herbaceous dicots, do not

have a central core of pith

7. True and often abundant secondary growth occurs in many species because of

the presence of vascular and cork cambium

8. Examples of dicots include many annual plants (such as tomatoes, peppers,

beans, sunflowers, mustards, and common weeds), flowering herbaceous spe­cies, and most flowering trees and shrubs