Monocots

A. Kingdom and classification

Taxonomy of monocots
1. Monocots are named differently depending on what naming system is used. This outline uses APG II (Angiosperm Phylogeny Group), which was revised in 2003 and is a common system to use. This system is based on cladistic analysis of DNA sequences on three genes (two chloroplast genes and one gene that codes for ribosomes)

i. APG uses cladistics. A clade is a group of organisms consisting of a single common ancestor and all descendants of that ancestor (monophyletic).

Monocots are classified as follows:

i. Domain Eukarya

ii. Kingdom Plantae

iii. Phylum Angiosperm (flowering plants numbering about 257,000 species)

1. Greek: angion= vessel; sperma=seed

iv. Clade monocots

1. Greek: mono=one; kotyledon: cup shaped hollow

2. monocot embryo produces single cotyledon (seed leaf)

v. Orders (-ales)

1. Acorales (single genus)

2. Alismatales (usually herbaceous and found in aquatic environments)

3. Asparagales (orchids)

4. Dioscoreales (terrestrial, herbaceous)

5. Liliales (lilies)

6. Pandanales (palm-like, climbing, and herbaceous plants)

vi. Clade commelinids (a clade within the monocots)

1. Commelinids: A monophyletic group of monocotyledonous angiosperms that are united by DNA sequence data.

vii. Orders

1. Arecales (palms)

2. Commelinales (herbaceous)

3. Poales (grasses and many crops such as rice, wheat, maize, sugar cane, and pineapple)

4. Zingiberales (terrestrial, tropical; includes ginger, banana)

*These are the main orders of monocots. Each order contains one to many families and some of the main families will be discussed later.

B. General Morphology/Biology

1. Angiosperm Characteristics

a. Produce flowers (reproductive structures)

b. Have endosperm: food storage tissue that provides nutrients to developing embryo

c. Produce modified leaves grouped into flowers that in turn develop into fruit and seeds

d. Advanced vascular system (xylem and phloem)

2. Monocot Characteristics

a. Many produce single flower at tip of shoot (lily) or can exhibit inflorescence (stalk with numerous flowers).

b. Many seed plants increase diameter through secondary growth via the vascular cambium. This produces wood and bark. Monocots do not have a vascular cambium and so do not perform secondary growth.

c. Palm trees have thick stems because they have wide apical meristem (gives rise to primary plant body) and dead leaf bases.

d. Monocot roots have vascular tissue that surrounds the pith(central area)

e. All plant cells contain plastids (chloroplasts, chromoplasts, etc.), some of which become photosynthetic, but those found in the phloem tissue do not. These plastids contain crystalloid proteins and the shape of these proteins is different for different major groups of plants. In monocots, they are triangular.

f. Stomates in monocots are usually in parallel rows.

3. Comparison of monocots vs. dicots

Monocots	Dicots
1 Cotyledon	2 Cotyledons
Parallel-veined, elongated leaves	Reticulate, net-veined leaves
Scattered primary vascular bundles in stems	Stem vascular bundles in a ring
Pollen monosulcate	Various types of pollen, often tricolpate
Root system adventitious, fibrous	Primary root, tap root
Floral parts in multiples of 3	Floral parts in 4’s or 5’s
No Vascular Cambium	Vascular Cambium present
Secondary growth absent	Secondary growth often present
Less than 10% woody	About 50% woody

a. Terms to know

i. Cotyledons: seed leaves produced by the embryo. They absorb nutrients packaged in the seed until the seedling is able to produce its first true leaves and begin photosynthesis.

ii. Monosulcate: Pollen with single pore

iii. Adventitious roots: roots arise from the stem and not another root.

iv. Fibrous roots: have large surface area for absorption of H₂O and minerals; cling to soil well

C. Evolution

Angiosperm evolution
1. Darwin called the origin of angiosperms an “abominable mystery”.
2. Apparent “burst” of angiosperms into fossil record without transitional forms has led researchers to look for origin
3. End of Paleozoic era (260 mya) climate became cooler and drier. The swampy plants that dominated previously, died. The gymnosperms (seed-bearing plants) survived the drier conditions
4. Mesozoic era (252-65 mya) saw conifer diversity worldwide
5. Mid-Cretaceous period (100 mya) saw a great angiosperm radiation and by late Cretaceous, angiosperms appear to have become the predominant group of land plants.
6. It is believed that Gymnosperms (naked seed) were precursor to angiosperms. Importance of seed includes:

i. Enabled plants to diversify and adapt to range of different environments

ii. Seeds were able to be dispersed long distances by air or animals and remain viable for long periods of time. This led to more diversification.

iii. When conditions are favorable, seed can germinate and become new plant

iv. This innovation allowed plants to inhabit inhospitable climates

A group of Gymnosperms believed to be ancestors of angiosperms are called Gnetales, which includes

i. Gnetum gnemon has leaves and vessels in xylem that are much like angiosperms

Two competing hypotheses for angiosperm origins (woody vs. herbaceous)

i. Woody Magnoliid Hypothesis favors an early angiosperm with morphology similar to living members of the Magnoliales. This theory suggests basal lineages were small trees with slower life cycles

ii. Paleoherb Hypothesis favors tropical, herbaceous paleoherbs which are a group of flowering plants with uncomplicated flowers and a mix of monocot and dicot features. It’s been suggested that climate and geography changes provided opportunities for these early angiosperms to diversify.

If early angiosperms were herbaceous, that would enable them to seed new ground quickly due to their shorter life cycles than woody plants. This would enable them to evolve and diversify quickly.
Whether herbaceous or woody, early angiosperms radiated because of development of the flower.
Flower petals didn’t evolve until between 90 and 100 mya and they started out very small, but it is likely that insects began pollinating flowers as soon as they existed.
Interaction between insects and flowering plants has shaped the development of both groups (coevolution).
After dinosaurs became extinct, mammals continued to evolve and eat angiosperms. This meant even more seed dispersal.

Monocot Evolution
1. There are many more fossils of dicot leaves than monocot
2. Angiosperms probably separated into monocots and dicots in the mid-Cretaceous period.

D. Major Groups of Organisms and Descriptions

1. Orchids (Family Orchidaceae, Order Asparagales)

a. One of the largest families of flowering plants

i. Contains 1,000 genera and about 20,000 species

b. Herbaceous perennials: their above ground tissues die back periodically

c. Terrestrial Orchids:

i. Perennating tissues in the surface substrate of the ground or the surface sediment or peat of a wet meadow

d. Epiphytic Orchids:

i. Use taller plants as a platform upon which to grow within the canopy.

ii. Do not obtain any of their moisture or nutrients from their host.

e. Leaves:

i. Usually arranged alternately on their stem, or are basal around the flowering stalk

ii. Simple, have non-toothed margins, are usually strap-shaped or linear, have a longitudinally parallel venation, and a sheath to their base (lack petiole)

f. Flowers:

i. Strongly zygomorphic, and are perfect, containing both female and male reproductive structures.

ii. Born singly or as a group

iii. Three sepals which may be green or colorful and petal-like, and there are three petals

iv. Two lateral petals are called wings and are mirror images of each other

v. Central petal is called the lip

1. Serves as a landing platform for pollinating insects

2. Commonly has a nectar-bearing sac or spur

vi. There are one or two stamens that are united with the stigma and style to develop a composite structure called the column.

vii. During development the flower of many orchids twists 180 degrees on its supporting stalk so the mature flower is actually presented upside down.

2. Palms (Order Pandanales)

a. Contains about 5 families, 212 genera and 2,800 species.

b. Mostly unbranched shrubs or trees and are the main tree family within the monocotyledons.

c. Large, persistent leaves that are sheathing at the base typically crown the solitary erect stem.

d. Leaves:

i. Occasionally simple

ii. Usually they are dissected into a fan shape (palmate)

iii. Or feathered shape with many distinct segments that run perpendicular to the main axis of the leaf.

iv. Stem may be short, almost might seem absent

v. Some palms have clustered stems that arise from buds at the base of the initial stem

e. Secondary growth is absent in palms

i. When a seed germinates, the seedling first grows into an inverted cone whose width matches the full width of the trunk

ii. After this radial growth is completed the seedling begins to grow vertically

f. Flowers:

i. Occasionally bisexual but usually unisexual

ii. Small and generally borne on large, many branched stems

3. Lily (Family Liliaceae, Order Liliales)

a. About 240 genera and 4,000 species

b. Mostly perennial erect herbs arising from a bulb

c. Most arise from underground stems or other structures but some climb and a few are woody.

d. Leaves:

i. Vary in number from one to many

ii. Arranged on the stem alternately or in whorls

iii. Flat, linear to lance-shaped

iv. No teeth along the margins and often widen into a papery sheath where they attach to the stem

v. Lack stalks

vi. Typically parallel veined

e. Flowers:

i. Trumpet or funnel shaped

ii. Nodding

iii. Heavily scented

iv. Bisexual, radially symmetrical

v. Parts are usually in some multiple of three

vi. No distinction in the appearance of petals and sepals

vii. Usually six main segments to the showy part of the flower

viii. May occur singly at the top of a leafless stem, as several flowers arranged on a spike, or in various other arrangements.

ix. Flowers are insect pollinated

f. Fruits: either capsules or berries

4. Grasses (Family Poaceae, Order Poales)

a. As many as 10,000 species of grasses among the 600 genera

b. Shoots

i. Typically have swollen nodes or bases

ii. Often hollow between the nodes

c. Leaves

i. Usually long and narrow

ii. Parallel veins

iii. Specialized tissue called a ligule is usually present at the location where a leaf sheaths to the stem

d. Flowers

i. Typically small, monoecious or dioecious and are called florets

ii. Florets have specialized tissue, often contain a long bristle called an awn, which can be quite prominent in some species

iii. Florets often arranged into a cluster

e. Fruit: known as caryopsis or grain

i. One seeded

ii. Can contain a large concentration of starch.

E. Distribution of the organism in the biosphere

1. Due to the wide variety of angiosperm monocots, there is a huge diversity in the biosphere. Many of these monocots inhibit many different climates/environments in almost everywhere in the world.

A. Grasses

i. Can be found in all climate types: hot, dry, humid, cold, etc.

ii. Located in meadows, prairies, grasslands, rain forests, deserts, mountains, pastures, etc. (Everywhere except Antarctica).

B. Lilies

i. Are usually located in northern regions: Europe, Asia, Japan, India, United States, and Canada.

ii. Typically inhabit woodlands, grasslands, and marshes.

C. Orchids

i. Are located in every type of habitat except Antarctica and deserts.

ii. Found all over the world

D. Palms

i. Located in habitats ranging from deserts to rain forests.

ii. Most abundantly located in tropical regions.

F. Organism’s adaptations to the environment

1. All of the angiosperm monocots have similar adaptations depending on the environments they inhabit.

2. Those that exist as perennials will die off in the winter and grow once again in the summer.

A. Grasses

i. Some grasses are drought resistant and also have an ability to undergo drought recovery.

ii. Some are able to protect themselves from the cold season.

iii. Grasslands (multiple species of grass):

a. Able to withstand high winds and long periods of dry weather

b. Can survive after a fire.

c. Can change their growth rate to accommodate the seasons, i.e. grow more in warmer temperatures than in cold temperatures.

B. Lilies

i. When located in dry regions, the roots grow deep.

ii. Adaptations to water environments:

a. Have large flat leaves and air pockets to help them float.

b. Are less rigid

c. Their roots are feathery and small because they don’t need support and they also diffuse most of their oxygen and water through their leaves.

C. Orchids

i. Have adapted to almost all climates.

ii. Leaves are covered in a waxy substance in some orchids.

iii. Depending on the location, the flowers may be specialized to appeal to certain insects necessary for pollination.

iv. Vine like orchids:

a. Have the ability to climb as they grow giving it the vine like properties.

b. Have spongy roots that allow the orchid to absorb essential minerals and water from the dead bark of the trees it grows on.

D. Palms

i. Thick dense trunks composed of scattered vascular bundles with no secondary growth.

ii. Become woody as they mature.

iii. Growth height depends if adapting to shade or not. If not in tropical forests, palms grow high enough to form part of the canopy.

iv. Desert conditions:

a. Roots grow to the depths of underground water supply.

b. Can survive for extended periods of time without rainfall.

c. Palm leaves are resistant to sun damage.

G. Life cycle and reproduction methods

1. Life cycle is the same as lower plants with the exception of the gametophyte phase.

2. Two types of spores are produced: megaspores and microspores.

3. Developing the male gametophyte:

i. Microsporocytes in each of its four chambers, undergoes meiosis which produces quartets of microspores.

ii. Mitosis takes place.

iii. The quartet cells separate becoming pollen grains.

iv. Pollen sacs develop in which the pollen grains are released through the openings.

v. Pollination may occur.

vi. If so pollen grains produce pollen tubes.

vii. The germinated pollen grain is the male gametophyte.

4. Developing the female gametophyte:

i. Megasporocytes in the ovule go through meiosis, which produces four haploid megaspores.

ii. Only one megaspore gets larger with mitotic divisions.

iii. This results in eight nuclei which is the female gametophyte.

iv. The egg is usually one of the lower nuclei.

5. After pollination the pollen tube contents are moved into the pollen sac.

6. Double fertilization occurs when the sperm and the egg unite forming a zygote and sperm and the polar nuclei unite forming the endosperm nucleus.

7. The endosperm contains three chromosomes which is a triploid.

8. Repeated division occurs producing the food storing endosperm tissue

9. Outer layers of the ovule harden creating the seed coat.

10. Seeds mature into fruit.

H. Economic Uses

Grasses

The grass family is the most important family in terms of the economic and nutritional values of foods it provides for humans and domestic livestock.

i. Wheat

1. Bread wheat is a very important grain species.

2. The “soft” wheat is mostly used for baking breads and pastries

3. The “hard” wheat is used to prepare pastas and other types of noodles.

4. Wheat is manufactured into:

a. Flour: used to bake breads, sweetened cakes, and pastries, pastas and noodles.

b. Breakfast cereals

c. Grains are fermented in a mash to produce beer and other alcoholic beverages and also industrial alcohol.

d. Wheat hay and straw are used as a fodder for animals.

ii. Maize or corn

1. Used for direct consumption by humans as:

a. Sweet corn is eaten after boiling or steaming

b. Eaten as cooked porridge made of ground meal (grits)

c. Also includes foods such as:

i. Canned or frozen cooked kernels

ii. Corn flakes

iii. Tortillas

iv. Corn chips

v. Popcorn

d. In some regions (Midwestern US), maize production is utilized to manufacture ethanol for use as a fuel in automobiles

iii. Rice

1. Mostly eaten steamed or boiled

2. Can be dried and ground into flour.

3. Rice straw can be used to make paper and can also be woven into mats, hats and other products.

iv. Barley

1. Used to feed domestic animals

v. Rye

1. Flour used to make rye breads and crisp breads

vi. Oats

1. Used as fodder for cattle and horses and for some breakfast foods.

vii. Sugar Cane

1. Most is manufactured into refined sucrose, or table sugar

viii. Bamboo

1. Bamboo canes are split and used for thatching and young shoots can be steamed or boiled and eaten as a vegetable.

Palms
1. Palms rank second in economic importance after the grasses.
2. Palms are used for food, oil, fiber, and as ornamentals

i. Food:

1. Dates are the fruit of the date palm (Phoenix dactylifera)

a. Usually eaten fresh but can be made into a paste

2. Coconuts are the fruit of the coconut palm (Cocos nucifera)

a. 30 billion coconuts are produced each year

b. most of the harvest if used for the production of coconut oil

c. Sago, derived from the pith of the sago palm (Metroxylon sagu), is an important source of carbohydrate for many people of the tropics.

ii. Oil:

1. A number of palms are major sources of edible oils that are refined into cooking oil, margarine, and shortening.

2. Palm oils are also used in the manufacture of candles, soaps, lubricating greases, and stabilizers in plastic and rubber compounds.

3. African oil palm (Elaeis guineensis) is the single most important oil-producing palm, having recently surpassed the coconut.

iii. Fiber:

1. Shells of the coconut are covered by tough fibers which are collected by soaking the shells in salt water to loosen the fibers. Fibers are then beaten, washed and combed out. Used as stuffing and woven into mats

iv. Ornamentals:

1. Symbol of the tropics and many have been selected and grown for their beauty.

Lily Family
1. Highly prized as house and garden ornamentals
2. Many lilies have enchanting fragrances that are sometimes extracted for use in perfumes.
3. Young shout of asparagus (Asparagus officinalis) are an important cash crop.
4. Wild sarsaparilla (Avalia nudicaulis) has long been an ingredient of soft drinks, and aloe (Aloe vera) is used as a salve in the treatment of burns and in cosmetics.
5. Meadow saffron (Colchicum autumnale) was used to treat gout.
Orchid Family
1. Commonly cultivated in greenhouses, homes, and in warm and humid climates, and in outdoor gardens. Most popular horticultural orchids are Catteleya, Cymbidium, Dendrobium, Epidendrum, and Vanda.
2. Only food obtained from orchid family is vanilla, which is extracted from the ripe, seed-bearing fruits, or “beans,” of the vanilla orchid (Vanilla fragrans).

I. Study

Chemical Composition and Response to Dilute-Acid Pretreatment and Enzymatic Saccharification of Alfalfa, Reed Canarygrass, and Switchgrass.

1. What: Alfalfa (dicot), reed canarygrass (monocot), and switchgrass (monocot)

were evaluated for their bioconversion potential as energy crops.

Each of these plants are perennial herbaceous species that have potential as biomass energy crops in temperate regions.

Methods:
1. Each species was harvested at two or three maturity stages and analyzed for carbohydrates, lignin, protein, lipid, organic acids, and mineral composition.
2. Species were pretreated with dilute sulfuric acid at two temperatures and then were subjected to enzymatic saccharification ( the process of breaking a complex carbohydrate (as starch or cellulose) into its monosaccharide components)
3. Acid-released sugars and cellulose degradability of the biomass samples were determined.
Results:
1. More mature biomass samples of all forage species contained less protein and mineral constituents than immature harvests.
2. Alfalfa contained the most protein of the biomass samples
3. Reed canarygrass had more minerals and less lignin than the other biomass samples.
4. The two monocots contained more storage carbohydrates (starch and/or fructose) than the alfalfa stems.
5. Cell wall polysaccharides of the grasses were richer in non-glucose residues than alfalfa stems, but cell wall glucose content of the biomass samples was similar.
6. The alfalfa required a higher acid loading to achieve the same final pretreatment pH as the grasses.
7. Efficiency of glucose release was negatively correlated with Klason lignin content of the biomass samples
Implications:
1. Production of ethanol from corn and other grain crops fulfills approximately 3% of the U.S. automotive fuel needs.
2. Converting energy crops to ethanol may be beneficial because they can be grown on otherwise marginal crop lands (this will increase the land available for producing biomass).
3. This could be useful to farms who would like to gain more profit by being able to use the land that is not suitable for cultivating grains. This can also help ethanol producers who are looking for future feedstock to supplement grains.

References

Dien, Bruce, et al. “Industrial Robust Enzymes and Microorganisms for production of

Sugars and Ethanol from Agricultural Biomass.” Biomass and Bioenergy (2006):

n. pag. 20 Oct. 2006.

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