PHYTOGEOGRAPHY
INTRODUCTION
• Phytogeography or plant geography is the
study of the origin, environmental relations
and global distribution of plants both in time
and space
• It has two basic aspects
– Historical
– Ecological
Historical aspects
• The historical aspects of phytogeography deals
with the distribution of plants in the past, and
also with their evolution and dispersal I course
of time
Ecological aspects
• The ecological aspects of phytogeography is
cocerned with the geographical distribution of
plants in relation to environment and other
ecological factors
Branches of Phytogeography
• Descriptive/Static phytogeography
• Interpretive/Dynamic phytogeography
Descriptive Phytogeography
• This is the branch of phytogeography that
deals with the distribution of plant
communities in the different geographical
regions of the world. In it, earth surface is
divided into distinct floristic or botanical
regions or zones for the convenience of
systematic description
Interpretive phytogeography
• This is the branch of phyteogeography that deals with
the impelling causes, the probable methods and the
essential conditions of plant distribution and also
with the dynamics of the migration and evolution of
the plants
• It analyses the reason behind the varied distribution
of plant species in the different parts of the world
• It utilizes the information from various branches like
ecology, evolution, physiology, genetics, taxonomy,
palaentology and geology for the analysis
SIGNIFICANCE OF PHYTOGEOGRAPHY
• Provides a clear picture of the vegetational types of the
past and the present
• Elucidates the distribution of the different groups of plants
all over the world
• Reveals the centres of origin and the course of migration
of the different groups of plants
• Explains the abiotic and biotic factors and conditions
which control the distribution of plants on the earths
surface
• Enables an understanding of the climatic conditions and
the vegetational types of an area in the remote past
• Provides information regarding the pattern of floristic
evolution in a geographical zone
PRINCIPLES OF PHYTOGEOGRAPHY
• Ronald Good and Mason have proposed some basic
concepts regarding the distribution of plants and are
called the Principles of Descriptive phytogeography
• They are thirteen in number and are classified under
four groups
– Principles related to environment
– Principles related to plant responses
– Principles related to the migration of floras and climaxes
– Principles related to the perpetuation and evolution of
floras and climaxes
Principles concerned with environment
• Climatic control is primary and there is parallelism
between climate and vegetation
• Climate has significantly changed in the past and there
is always oscillation of climatic conditions from time to
time
• The relation between land and sea has changed in the
past
• Edaphic control is secondary in plant distribution
• Biotic factors are also important in plant distribution
• Environment is holocentric
Principles concerning plant responses
• The geographic or climatic ranges and
distribution of plants are determined by their
tolerance
• Tolerance of plants has a genetic basis
• Different ontogenic stages have different
degrees of tolerance
Principles concerned with the migration of
floras and climaxes
• Migrations of floras have occurred in the
remote geological past and are still continuing
• Migration involves transport and it results in
establishment
Principles concerning the perpetuation and
evolution of floras and climates
• Perpetuation depends on migration and
evolution
• Evolution of floras and climaxes depends on
migration, evolution of species and natural
selection
