BIOLOGY PROJECT
PLACENTATION
Definition
Placentation is defined as the arrangement of the ovules within the ovary. The
use of rules are attached to the ovary by fleshy structures called placentae
(singular placenta) through short stalks called funicles.
Types
Marginal Placentation
Parietal Placentation
Free Central Placentation
Axile Placentation
Basal Placentation
MARGINAL PLACENTATION
In this type of placentation, the ovules are attached to the placenta along
one margin of a unicarpellette ovary. Example; Beans.
PARIETAL PLACENTATION
In this type of placentation almost are attached to decide of a syncarpous
ovary having a single chamber, i.e they are attached to the inner walls of a
compound ovary, specifically along the margins of fused carpels.
Example;Pawpaw.
FREE CENTRAL PLACENTATION
This is a type of placentation in plants where the ovules are attached to a
central column or axis in the ovary, but not to the ovary walls. It is a type of
placentation where ovules develop on a central column within a compound ovary,
which either lacks septa (partitions) or has them only at the base.Example; Cana
lily.
AXILE PLACENTATION
This type of placentation involves the meeting of the carpels of a
syncarpous ovary at the center to form the placenta to which the ovules are
attached. Examples; Tomatoes.
BASAL PLACENTATION
This is a type of ovule arrangement in flowering plants where the ovules
(potential seeds) are attached to the base of the ovary.Examples; Sunflower.
Importance
Placentation is crucial in plant anatomy as it plays a significant role in plant
identification, classification, understanding reproductive biology, evolutionary
studies, and taxonomy. By studying placentation, botanists can gain valuable
insights into plant diversity and evolution.
FACTORS TO CONSIDER WHEN CLASSIFYING FLOWERS
Factors to consider when classifying flowers include their structure, such as the
number and arrangement of floral parts, the presence or absence of male and
female reproductive organs, and the symmetry of the flower. That is;
STRUCTURE
Flowers can be classified into a complete an incomplete flowers
according to their structure. Complete flowers have all four floral parts such
as the petals, sepals, stamens and pistils, unlike incomplete flowers which
do not have all four floral parts.
SYMMETRY
Actinomorphic flowers which have radial symmetry e.g roses, and
zygomorphic flowers which have bilateral symmetry e.g orchids,are
examples of flowers which are classified by symmetry.
INFLORESCENCE
Flowers can be classified by the way they are arranged on a plant
stem, For example, Solitary flowers are just single flower on a single stem while,
Clustered flowers are multiple flowers on a plant stem.
Others include; Number of cotyledons(dicots and monocots),Life
cycle(annuals, perennials and biennials).
Note: The classification of flowers also depends on the type of plants in
which they are found.
CLASSIFICATION OF FLOWERS BASED ON THE NUMBER OF FLORAL
PARTS
Classification by Number of Petals:_
- Monopetalous (one petal, e.g., some Orchids)
- Polypetalous (many petals, e.g., Roses, Carnations)
- Apetalous (no petals, e.g., some flowers in the Euphorbia family)
Classification by Number of Sepals:_
- Monosepalous (one sepal, rare)
- Polysepalous (many sepals, e.g., Roses)
Classification by Arrangement of Floral Parts:_
- Cyclic (whorled arrangement, e.g., Roses)
- Spiral (helical arrangement, e.g., some Magnolias)
Classification by Number of Stamens:_
- Monandrous (one stamen, e.g., some flowers in the Cannaceae
family)
- Diandrous (two stamens, e.g., some flowers in the Oleaceae family)
- Polyandrous (many stamens, e.g., Roses, Hypericum)
Classification by Number of Carpels:_
- Monocarpellary (one carpel, e.g., Legumes)
- Polycarpellary (many carpels, e.g., Roses, Apples).
Classifying flowers based on the number of floral parts is
crucial for plant identification, understanding evolutionary relationships,
and practical applications in horticulture, gardening, and botanical
research. It helps distinguish between species, group plants, and inform
plant breeding and conservation efforts, ultimately providing insights
into plant diversity, evolution, and ecology.
