Interrelationship among the major groups of angiosperms.pdf

Angiosperms
Major groups
Inter relationship
Evolutionary trends

Dr. Praveen Mohil
Assistant Professor
Department of Botany, university of Rajasthan

Simplify Plant Taxonomy

1. What are the major groups?
Interrelationship among the major groups of angiosperms?
Evolutionary Trends in Angiosperms.



Dr Praveen Mohil
Assistant professor
Department of Botany
University of Rajasthan, Jaipur


Introduction-
Angiosperms, or flowering plants, are the most diverse group of plants, and their
classification is complex.Understanding the interrelationships among the major groups of
angiosperms has been a long-standing question in plant evolutionary biology.
The major groups of angiosperms—monocots, eudicots, and basal angiosperms—are
interrelated through their evolutionary history.
Monocots and eudicots represent two major branches of angiosperm evolution, while basal
angiosperms are considered more primitive relatives that provide insights into the early
evolution of flowering plants.
However, their major groups are typically divided into two broad categories: monocots and
dicots (now more commonly referred to as eudicots).
What are the Monocots, Eudicots & Basal Angiosperms?
Monocots: These plants have one cotyledon (seed leaf) in the embryo, parallel-veined
leaves, and flower parts typically in multiples of three (trimerous fls). Monocots also tend
to have scattered vascular bundles (stem) and a fibrous root system. Major families
include grasses (Poaceae), lilies (Liliaceae), and orchids (Orchidaceae).
Eudicots: These plants have two cotyledons, net-veined leaves (reticulate venation), and
flower parts often in multiples of 4 or 5 (tetra merous/pentamerous fls.). Eudicots usually
have vascular bundles arranged in a ring and a taproot system. They include a wide variety of
plants such as roses (Rosaceae), sunflowers (Asteraceae), and legumes (Fabaceae).
Basal Angiosperms: These are the early-diverging groups of angiosperms that don't fit
neatly into either monocots or eudicots. They exhibit a mix of characteristics found in both
monocots and eudicots and are considered more primitive in evolutionary terms. They
include families like magnolias (Magnoliaceae) and water lilies (Nymphaeaceae).

2. Major Groups of Angiosperms @ characteristics and examples
1. Basal Angiosperms: These are the earliest diverging lineages within angiosperms. They
are small groups that share primitive characteristics with gymnosperms and other seed plants.
Characteristics: These are considered the most primitive and include plants that diverged
early from the main angiosperm lineage. They often have features that are somewhat
intermediate between monocots and eudicots.
Key groups include:
Amborellales: Represented by Amborella trichopoda, endemic to New Caledonia. It is
often considered the most basal extant angiosperm.
Nymphaeales: Water lilies and their relatives.
Austrobaileyales: A small group that includes Austrobaileya and other species, mostly
distributed in tropical and subtropical areas.
Examples: Magnolias (Magnoliaceae): Have large, showy flowers with many spirally
arranged floral parts. Water Lilies (Nymphaeaceae): Aquatic plants with floating leaves and
large, showy flowers.
2. Monocots:
Characteristics: Characterized by having one cotyledon (seed leaf), parallel-veined leaves,
and floral parts typically in multiples of three. Vascular bundles are scattered throughout the
stem.
Examples: Grasses (Poaceae): Includes important crops like wheat, rice, and corn. Orchids
(Orchidaceae): Known for their complex and often intricate flower structures. Lilies
(Liliaceae): Includes ornamental plants such as tiger lilies and daylilies.
3. Eudicots:
Characteristics: Possess two cotyledons, net-veined leaves, and floral parts often in
multiples of four or five. Vascular bundles are arranged in a ring within the stem.
Examples:
Rosids: Includes a variety of economically and ecologically important plants.
Roses (Rosaceae): Includes not only ornamental roses but also fruit-bearing plants like
apples and strawberries.
Legumes (Fabaceae): Includes plants like beans, peas, and peanuts, which are significant
both ecologically and agriculturally.
Asterids: Another major group within eudicots.Sunflowers (Asteraceae): Includes both
ornamental and agricultural species such as sunflowers and daisies.Tomatoes (Solanaceae):
Includes important vegetables and fruits like tomatoes, potatoes, and eggplants.

3. Interrelationship among the major groups of angiosperms
The major groups of angiosperms are interrelated through their evolutionary history, with
basal angiosperms representing early divergents and monocots and eudicots reflecting major
evolutionary branches. Each group exhibits unique adaptations and characteristics that reflect
their evolutionary paths and ecological niches.
The interrelationship among the major groups of angiosperms (flowering plants) can be
understood through their evolutionary history and key characteristics.
1. Evolutionary Relationships:
Basal Angiosperms: Represent the earliest divergence in the angiosperm lineage, providing
insights into the primitive features of flowering plants. They are the outgroup to the more
derived groups (monocots and eudicots).
Monocots and Eudicots: These two groups represent the major divergence within the
angiosperms. The split between monocots and eudicots occurred relatively early in
angiosperm evolution.
2. Shared Characteristics:
Monocots and Eudicots: Both share common angiosperm features such as the presence of
flowers and fruits, which distinguish them from non-flowering plants like
gymnosperms. However, their differences in floral structure, leaf venation, and seed
structure are significant.
3. Evolutionary Adaptations:
Monocots: Often adapted to different ecological niches, including grasslands and tropical
environments. Their adaptations include variations in root systems and leaf structures that
help them thrive in these niches.
Eudicots: Show a wide range of adaptations due to their diverse subgroups (e.g., Rosids and
Asterids). This diversity includes variations in flower structure, fruit types, and ecological
roles.
4. Ecological and Economic Importance:
Monocots: Important for agriculture (e.g., cereals) and horticulture (e.g., orchids).
Eudicots: Include many plants with significant ecological roles (e.g., legumes in nitrogen
fixation) and economic value (e.g., fruits, vegetables).

4. Evolutionary Trends in Angiosperms
@Critical Note on Evolutionary Trends in Angiosperms
The evolution of angiosperms (flowering plants) marks a significant chapter in
plant history, shaping the biodiversity and ecology of modern ecosystems. As
the most diverse group of land plants, angiosperms exhibit a range of
evolutionary trends that highlight their adaptation, diversification, and
dominance over other plant groups. These trends reflect both morphological and
ecological changes that have enabled angiosperms to occupy diverse habitats
and survive various environmental challenges.
1. Diversification of Flower Structure
• Trend: From simple to complex floral structures.
• Analysis: Early angiosperms, like those of the basal group (e.g.,
Amborella), tend to have simple flowers with undifferentiated floral parts.
Over time, angiosperms evolved more specialized flowers with clear
differentiation between sepals, petals, stamens, and carpels. These
modifications enhanced reproductive efficiency, including specialized
mechanisms for attracting pollinators. Complex floral structures in
advanced angiosperms (e.g., orchids, sunflowers) show intricate
pollination strategies involving specific animals.
• Significance: The diversification of floral morphology contributed to the
wide ecological success of angiosperms by facilitating cross-pollination
and enhancing genetic variability.
2. Reduction in Gametophyte Size
• Trend: Reduction in the size and complexity of the gametophyte
generation.
• Analysis: Over evolutionary time, angiosperms have shown a
pronounced reduction in the size of both the male and female
gametophytes. The male gametophyte (pollen grain) is highly reduced to
just a few cells, while the female gametophyte (embryo sac) has been
simplified to a structure with only 7 cells and 8 nuclei.
• Significance: This reduction allows for faster reproduction cycles and
greater efficiency in seed production, giving angiosperms a competitive
advantage in diverse and changing environments.

5. 3. Vessel Element Development
• Trend: Evolution of efficient vascular tissue, particularly the
development of vessel elements.
• Analysis: Early angiosperms, like Amborella and members of the
Winteraceae family, lack vessel elements, relying solely on tracheids for
water transport. However, more derived angiosperms developed vessel
elements, which are larger and more efficient for water transport. This
allowed angiosperms to thrive in a wider variety of habitats, particularly
in drier environments where efficient water transport is critical.
• Significance: The development of vessels was a key innovation in
angiosperms, contributing to their ecological success by allowing them to
dominate terrestrial environments, especially in arid or seasonally dry
regions.
4. Coevolution with Pollinators
• Trend: Increasing coevolutionary relationships between angiosperms
and animal pollinators.
• Analysis: The early angiosperms were likely wind-pollinated, similar to
modern gymnosperms. Over time, many angiosperms evolved intricate
relationships with pollinators such as insects, birds, and mammals. These
plants developed traits such as brightly colored flowers, nectar
production, and fragrances to attract specific pollinators, resulting in
highly specialized pollination mechanisms.
• Significance: The coevolution with pollinators allowed for greater
reproductive success and the colonization of diverse ecological niches.
This also led to adaptive radiation and the explosion of angiosperm
diversity seen today.
5. Seed and Fruit Evolution
• Trend: Evolution from basic seed forms to highly specialized seeds
and fruits.
• Analysis: Early seeds were relatively simple, relying primarily on gravity
or wind for dispersal. Over time, angiosperms developed more
specialized seeds and fruits that employ various dispersal mechanisms,
such as being carried by wind, water, or animals. Some angiosperms
evolved fleshy fruits to attract animals, which in turn aid in seed
dispersal.

6. • Significance: The diversity in seed and fruit types enabled angiosperms
to spread across a variety of ecosystems. Seed and fruit specialization
enhances the likelihood of seed dispersal to suitable environments,
contributing to the colonization of new habitats and the wide geographic
distribution of angiosperms.
6. Increase in Heterospory and Double Fertilization
• Trend: From homospory to heterospory and the development of
double fertilization.
• Analysis: While homospory (the production of one type of spore) is
common in lower plants, angiosperms exhibit heterospory (the production
of two types of spores: megaspores and microspores). Additionally,
angiosperms introduced the process of double fertilization, where one
sperm fertilizes the egg to form a zygote, and the other fuses with polar
nuclei to form endosperm, which nourishes the developing embryo.
• Significance: Double fertilization is a unique angiosperm feature that
maximizes reproductive efficiency and enhances seedling survival by
providing a nutritive tissue (endosperm) that supports early growth.
7. Reduction in Leaf Size and Increased Leaf Specialization
• Trend: From large, simple leaves to more specialized forms?
• Analysis: Early angiosperms, such as Magnolia, often had large, simple
leaves. Over time, many angiosperms evolved smaller, more specialized
leaves adapted to a range of environmental conditions. Some angiosperms
developed succulent leaves to store water, while others developed needle-
like leaves to reduce water loss.
• Significance: This trend toward leaf specialization allowed angiosperms
to adapt to diverse environmental conditions, from deserts to tropical
forests, further enhancing their ecological success.


Thank you