Weed Biology and Identification-201

Target students: M.Sc. Students in Weed Science

Lecture:

Dr. Majid AghaAlikhani (Ph.D.)

Academic position :

Associate Prof. of Tarbiat Modares Universitymaghaalikhani@modares.ac.ir

1

Basic Plant Structure

Roots

Stems

Leaves

General Organization

A plant has two organ systems:1. the shoot system

• Found above ground and includes the organs such as leaves, buds, stems, flowers (if the plant has any), and fruits (if the plant has any).

2. the root system• Found below ground and includes roots,

tubers, and rhizomes

Classifying PlantsNonvascular plants:• have no vessels• no stems• No leaves• No roots

Examples: Mosses & Liverworts

Classifying Plants

• have vessels to transport food and water

• Xylem: transports water

• Phloem: transports food & nutrients

• have roots, stems and leaves

Example: Grass, corn, trees, flowers, bushes

Vascular Plants:

Gymnosperm

• Flowerless plants• "naked seeds" • cone bearing plants (seeds grow on cones) • needle like leaves • usually stay green year round

Examples: pine trees & evergreens

Angiosperm

• flowering plants • seeds are enclosed in a fruit • have finite growing seasons • Examples: grasses, tulips, oaks, dandelions

• Divided into two main groups: Monocots & Dicots

Monocot Seed• Angiosperms that have 1 seed leaf (cotyledon) • parallel veins on leaves • 3 part symmetry for flowers • fibrous roots Example: lilies, onions, corn, grasses, wheat

Dicot Seed

• Angiosperms that have 2 seed leaves (cotyledons) • net veins on leaves • flowers have 4-5 parts • have a taprootExamples: trees and ornamental flowers  

A. MONCOTS B. DICOTS

1. Have only 1 cotyledon 1. Have 2 cotyledons

2. Fibrous roots 2. Thick single main roots called taproots

3. Long thin leaves with parallel veins

3. Fan-like leaves with net veins

4. Flower parts are in groups of 3’s

4. Flower parts are in 4’s and 5’s

5. Stem has vascular tubes that are scattered

5. Stem has vascular tubes that are organized

into rings

6. E.g. corn, wheat, grasses

6. E.G. beans, maples, peanuts, peas

Roots• Roots absorb NUTRIENTS and water• anchor the plant in the soil• provide support for the stem• store food• usually below ground

There are two major types of root systems in plants.. Taproot and fibrous root.

Root Types• Taproot systems have a stout main root with a limited number of side-branching roots. Examples of taproot system plants:

nut trees, carrots, radishes & dandelions. • Fibrous root systems have many branched roots. Examples of fibrous root plants:most grasses, marigolds and beans

StemsThe stem is the main trunk of a plant.• provide structure and support for leaves,

flowers and fruits• may also store food• carry nutrients and water

Most stems grow above ground BUT…many stems grow below ground or are ground hugging

Some modifications include:• bulbs, rhizomes, runners, tubers

Leaves• are lateral outgrowths from the stem• main function is food production through

photosynthesis

• most commonly flat, broad and green. • maximizes their function of absorbing

sunlight and transforming it into food.

BudsBuds are undeveloped shoots and flowers• classified terminal or lateral.• Terminal buds can be identified by their location

at the tip of a stem.• Lateral buds are located at the sides of the stem.

Cabbage and head lettuce are examples of very large terminal budsBrussels sprouts are edible lateral buds. Broccoli is an example of edible flower buds.

FlowersReproductive organ of the plant – produce seedsFlowers are usually both male and female The male part of the flower is the STAMEN The female part of the flower is the PISTIL

• See your sheet for more detail on flower anatomy

Flowers Continued

Other external parts of flowers include:• SEPALS - usually green and enclose other

parts of the flower in the bud.• PETALS are usually brightly colored and may• contain aromatic substances as well as

nectar glands.

MALE - STAMENS

Stamens produce pollen which contain the sperm

Stamens are made of a head called the anther and a stock called the filament.

FEMALE – PISTIL

Pistil holds the egg cells.

The pistil is made of a sticky head called the stigma, a stock called the style, and the ovary that holds the egg cells.

Petal

Corolla

Sepal

Pistil

Stamen

Calyx

Stigma

Style

Ovary

Pollen

Anther

Filament

FruitA ripened ovary or group of ovaries containing the seeds• the ovary enlarges forming the mature fruit.

A simple fruit forms from the ripening of the ovary of a single pistil.

• Eg. Tomatoes & oranges

More on classification of fruits!

More on Fruit

A complex fruit is derived from more than one ovary resulting in a clustering of smaller fruit elements• Eg. Raspberries, strawberries – not

really berries!

The parts of the flower and what part they become in the fruit.

Fruit or Vegetable??Botanically:• fruit always develops from a flower and is

composed of at least one ripened ovary. • a vegetable is any edible part of a plant other

than the flower.

Most people think:• a fruit is an edible plant part that is sweet and

eaten as a dessert. • vegetable is a plant part that is edible, but

not particularly sweet.

Which is it?

Many fruits, such as tomatoes, squash, cucumbers, corn and eggplant, are popularly called vegetables.

However, only one vegetable, rhubarb (the edible petiole), is used as a fruit.