SYLLABUS THEME B PLANT CLASSIFICATION & DIVERSITY B1: Naming and classification of organisms Biology of Plants - Raven et al. 2005 pp. 219-237 INTRODUCTION TO TAXONOMY Taxonomy Naming Describing Classifying Classification Grouping organisms by their similarities or relationships Systematics Analytical 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 structure 18th Century flower and fruit structures used in classification 1
NAMING OF ORGANISMS Why we use Latin names to name living organisms? Facilitates international science Initially short phrase, polynomial Mentha (genus name) Mentha floribus spicatis, foliis oblongis serrattis (phrase name) NAMING OF ORGANISMS Swedish Scientist Carolus Linnaeus (1707-1778) Binomial system of Nomenclature A plant is named according to the International Code of Botanical Nomenclature (I.C.B.N.) name consists of 2 parts (binomial): a generic name + a specific epithet Authority - Abbreviation of the person who first published the name Phaseolus vulgaris L. Genus - Capital letter Specific epithet - Small letter - Never stands alone 2
I.C.B.N. & PLANT NAMES plant 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 characteristics The aim of a taxonomic ranking (hierarchy) is to arrange the taxa in such a way to reflect at best the differences and similarities amongst them Each taxonomic level is more general than the one below it HIERARCHICAL CLASSIFICATION 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 3
B3: Kingdom Plantae THE FIVE KINGDOM SYSTEM Robert Whittaker Plantae Fungi Animalia Protista Eukaryotes Prokaryotes Monera THE THREE DOMAIN SYSTEM 4
FIVE KEY CHARACTERISTICS IN LAND PLANTS APICAL MERISTEMS Apical Developing meristemleaves Apical meristem Shoot 100 µm Root 100 µm ALTERNATION OF GENERATIONS gametophyte Mitosis Mitosis n n n Spores n n Gametes MEIOSIS FERTILIZATION 2n sporophyte 2n Zygote Mitosis WALLED SPORES PRODUCED IN SPORANGIA Spores Sporangium Sporophyte and sporangium of Sphagnum (a moss) MULTICELLULAR GAMETANGIA Archegonia and antheridia of Marchantia (a liverwort) Female gametophyte Sporophyte Gametophyte Archegonium with egg Antheridium with sperm MULTICELLULAR DEPENDENT EMBRYOS Male gametophyte Embryo Maternal tissue 2 µm Embryo of Marchantia 10 µm Wall ingrowths Placental transfer cell THE GROUPS OF PLANTS 5
Seed plants Gymnosperms Naked seeds Eg. pine, cycads Angiosperms Enclosed seed Eg. Proteaceae, Fabaceae Ovule is borne naked Ovule is enclosed in ovary A specimen of Welwitschia mirabilis living in Namib Desert, Namibia survives on fog 6
ANGIOSPERM CHARACTERISTICS Vascular plants Produce flowers and seeds enclosed in a fruit Life cycle: Sporophyte is dominant Gametophytes are reduced and dependant on the sporophyte ANGIOSPERM CHARACTERISTICS Heterosporous - having two types of spores Microspores pollen grain Megaspore embryo sac Double fertilization 2n zygote 3n endosperm DICOTS VS MONOCOTS 7