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SYLLABUS THEME BPLANT CLASSIFICATION

& DIVERSITY

B1: Naming and classification of organisms

Biology of Plants - Raven et al. 2005pp. 219-237

INTRODUCTION TO TAXONOMY

TaxonomyNamingDescribingClassifying

ClassificationGrouping organisms by their similarities or relationships

SystematicsAnalytical study of the diversity and relationships of organisms

HISTORICAL DEVELOPMENT

Theophrastus – 4th Century• 500 plants based on leaf characteristics

13th Century – Monocots / Dicots based on stem structure18th Century – flower and fruit structures used in classification

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NAMING OF ORGANISMS

Why we use Latin names to name living organisms?

Facilitates international science

Initially – short phrase, polynomialMentha (genus name)

Mentha floribus spicatis, foliis oblongis serrattis(phrase name)

NAMING OF ORGANISMS

Swedish Scientist –Carolus Linnaeus (1707-1778)Binomial system of NomenclatureA plant is named according to the International Code of Botanical Nomenclature (I.C.B.N.)

Phaseolus vulgaris L.

Genus- Capital letter

Specific epithet- Small letter- Never stands alone

name consists of 2 parts (binomial): a generic name + a specific epithet

Authority- Abbreviation of the person who first published the name

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I.C.B.N. & PLANT NAMESplant nomenclature is independant of zoological nomenclature;the rules of the code are retrospective;the names are published in Latin, irrespective of its origin;the nomenclature of any taxon is based on the priority of publishing;every taxon can have only one correct name & it is the oldest name according to the rules;the application of botanical names is determined by means of nomenclatural types (typification).

TAXONOMIC RANKING

Taxon – Group of organisms of which all members share certain common characteristicsThe aim of a taxonomic ranking (hierarchy) is to arrange the taxa in such a way to reflect at best the differences and similarities amongst themEach taxonomic level is more general than the one below it

CATEGORY NAME OF TAXON

DESCRIPTION

Kingdom Plantae Multicellular eukaryotic organisms, photosynthetic

Phylum Anthophyta Flowering plants with ovules born in a closed ovary

Class Monocotyledones Embryo with one cotyledon, flowers trimerous

Order Commelinales Reduced flower parts, elongated leaves and dry 1-seeded fruits

Family Poaceae Grass family. Reduced green flowers in spikelet. Fruit is a caryopsis (grain)

Genus Zea Tall annual grass with separate female and male flowers

Species Zea mays Only one species in genus - maize

HIERARCHICAL CLASSIFICATION

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B3: Kingdom Plantae

THE FIVE KINGDOM SYSTEM

Robert Whittaker

Plantae Fungi Animalia

Protista

Monera

Eukaryo

tes

Prokaryotes

THE THREE DOMAIN SYSTEM

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APICAL MERISTEMS

Apicalmeristem

Developingleaves

100 µm

Apical meristem

Root 100 µmShoot

gametophyteMitosis Mitosis

Gametes

Zygote

sporophyte

MEIOSIS FERTILIZATION

2n2n

n

nnn

nSpores

Mitosis

ALTERNATION OF

GENERATIONS

FIVE KEY CHARACTERISTICS IN LAND PLANTS

WALLED SPORES PRODUCED IN SPORANGIA

MULTICELLULAR GAMETANGIA

MULTICELLULARDEPENDENT EMBRYOS

SporesSporangium

SporophyteGametophyte

Sporophyte and sporangium of Sphagnum (a moss)

Female gametophyteArchegoniumwith egg

Antheridiumwith sperm

Malegametophyte

Archegonia and antheridia of Marchantia (a liverwort)

EmbryoMaternal tissue

2 µm

Wall ingrowthsPlacental transfer cell

10 µm

Embryo of Marchantia

THE GROUPS OF PLANTS

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Ovule is borne naked

GymnospermsNaked seeds

Eg. pine, cycads

Ovule is enclosed in ovary

AngiospermsEnclosed seed

Eg. Proteaceae, Fabaceae

Seed plants

A specimen of Welwitschia mirabilis living in Namib Desert, Namibia – survives on fog

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ANGIOSPERM CHARACTERISTICS

Vascular plantsProduce flowers and seeds enclosed in a fruitLife cycle:

Sporophyte is dominantGametophytes are reduced and dependant on the sporophyte

ANGIOSPERM CHARACTERISTICS

Heterosporous - having two types of sporesMicrospores – pollen grain

Megaspore – embryo sac

Double fertilization2n zygote

3n endosperm

DICOTS VS MONOCOTS