Basal angiosperms || Key Groups of Basal Angiosperms

What are the basal angiosperms?
Key Groups of Basal Angiosperms
Why Basal Angiosperms are Considered Primitive?
Key Examples of Basal Angiosperms

1. What are the basal angiosperms?
Key Groups of Basal Angiosperms
Why Basal Angiosperms are Considered Primitive?
Key Examples of Basal Angiosperms








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


YouTube Channel

https://www.youtube.com/@simplifyplanttaxonomy
&
https://www.youtube.com/@praveen_mohil

2. Introduction
Basal angiosperms are considered primitive because they retain many ancestral
traits that are believed to be characteristic of early flowering plants, which
diverged early from the common ancestor of all angiosperms.
These are a group of early-diverging lineages of flowering plants (angiosperms)
that are considered to represent some of the most primitive or ancestral, features
of the group.
These plants diverged early from the rest of the angiosperms and retain
characteristics that are thought to be similar to those of the earliest flowering
plants.
These traits are often less specialized and reflect a simpler form of plant
structure and function when compared to more derived groups like monocots
and eudicots.
Key Groups of Basal Angiosperms:
1.Amborellales: Amborella trichopoda is the sole species in this order and is
native to New Caledonia. It is often considered the most primitive living
angiosperm.
2. Nymphaeales:This order includes water lilies and their relatives. They are
aquatic plants with large, floating leaves and showy flowers.
3.Austrobaileyales:This order includes plants like Illicium (star anise),
Austrobaileya, and Schisandra. They are typically found in tropical and
subtropical regions.

3. Why They Are Considered Primitive:
A. Ancestral Traits: Basal angiosperms retain several traits that are considered
ancestral, or primitive, in comparison to more derived angiosperms (like
eudicots and monocots). These traits include:
Simple flower structure: Their flowers often have fewer parts that are arranged
in a spiral rather than in whorls.
Undifferentiated perianth: The perianth (collective term for petals and sepals)
is often not clearly differentiated into distinct petals and sepals.
Numerous and free parts: They often have numerous stamens and carpels that
are not fused, unlike the more complex structures seen in more derived
angiosperms.
Amborella's wood structure: Amborella lacks vessels in its wood, which is a
primitive trait; vessels are a more advanced feature found in most other
angiosperms.
B. Evolutionary Position: Molecular phylogenetic studies have shown that
these groups diverged early from the lineage that led to most other angiosperms.
This early divergence suggests that they have retained more of the
characteristics of the common ancestor of all flowering plants.
C. Ecological Habits: Many basal angiosperms occupy ecological niches
similar to those that might have been common when flowering plants first
evolved. For example, many are found in wet, shaded environments, which
could have been more prevalent during the early evolution of angiosperms.
Significance in Evolutionary Biology:
Studying basal angiosperms provides insights into the early evolutionary history
of flowering plants and helps researchers understand how more complex
structures and diversification arose in the more derived angiosperm lineages.

4. Why basal angiosperms are considered primitive?
1. Retention of Ancestral Traits
Basal angiosperms retain many characteristics that are considered primitive or ancestral
compared to the more derived traits seen in most modern flowering plants. These traits
include features of their flowers, vascular tissue, and reproductive strategies.
Basal angiosperms exhibit characteristics that are similar to those found in
gymnosperms (non-flowering seed plants) and other early-diverging seed plants. These
traits are thought to have been present in the earliest flowering plants.
Example: Amborella trichopoda (the only species in the Amborellales order) lacks vessels in
its xylem, a characteristic seen in more primitive plants like gymnosperms. Most other
angiosperms have more specialized water-conducting cells known as vessels.
2. Simple Floral Structures
In basal angiosperms, the flowers often have a less specialized structure. For instance, the
flowers tend to have numerous, spirally arranged petals, sepals, stamens, and carpels,
rather than the distinct and reduced number of floral organs typical of more advanced
angiosperms.
The flowers of basal angiosperms are often simple and unspecialized compared to those in
more derived groups. They tend to have fewer floral parts, and those parts are less
differentiated. In many cases, the floral organs are arranged in a spiral, a feature seen in
gymnosperms, rather than in distinct whorls.
Example: In Nymphaea (water lilies, part of Nymphaeales), the floral parts are often
numerous and spirally arranged, which is considered a primitive characteristic.
Example: Austrobaileya scandens (in the Austrobaileyales order) has large, simple, and
unspecialized flowers that exhibit spiral phyllotaxis, similar to early plant forms.
3. Undifferentiated Floral Organs
Basal angiosperms often have floral organs that are not distinctly separated into sepals,
petals, stamens, and carpels. In more derived angiosperms (monocots and eudicots), the floral
organs are usually clearly differentiated.
Example: In Amborella, the distinction between sepals and petals is not as clear, and the
flower parts are often intermediate in structure, a sign of primitive floral development.
4. Pollination Mechanisms
Pollen Structure: The pollen of basal angiosperms typically has a single pore or furrow
(monosulcate), which is considered a primitive characteristic, as opposed to the more
complex pollen structures seen in derived angiosperms.
The pollination mechanisms of basal angiosperms are generally less specialized. In contrast,
more derived angiosperms have evolved intricate relationships with specific pollinators,
such as bees, birds, or bats, leading to highly specialized flowers.

5. Example: In Nymphaea, the flowers are adapted for generalist pollination strategies,
attracting a wide range of pollinators rather than specialized pollinators, reflecting an
ancestral form of pollination.
5. Perianth Features
The perianth (the collective term for petals and sepals) of basal angiosperms is often
undifferentiated or poorly differentiated. This means that the sepals and petals are not
clearly distinct in size, shape, or function, which is seen as a primitive condition compared
to more derived groups where petals and sepals are highly differentiated.
Example: Austrobaileya has tepals, which are floral structures that are not clearly
distinguishable as either sepals or petals, a trait considered more primitive than the
differentiated sepals and petals of more advanced flowering plants.
6. Wood Anatomy
Wood Structure: The wood of basal angiosperms often lacks the advanced features found in
more derived plants, such as vessels, which are specialized cells for efficient water transport.
Basal angiosperms tend to have primitive wood anatomy, often lacking the more advanced
vessel elements seen in other angiosperms. Their wood consists primarily of tracheids, which
are less efficient in conducting water than the vessels found in more derived angiosperms.
Example: Amborella lacks vessels in its xylem, retaining only tracheids, a trait considered
more primitive and similar to that of gymnosperms.
7. Leaf Structure
The leaves of basal angiosperms often show characteristics similar to those of early seed
plants, such as simple venation patterns (either parallel or poorly defined venation) and a
lack of differentiation between upper and lower leaf surfaces.
Example: Leaves of Amborella are simple with undifferentiated mesophyll tissue, unlike
the complex leaf structures seen in more derived angiosperms.
Key Examples of Basal Angiosperms
1. Amborella trichopoda: The most primitive extant angiosperm, endemic to New
Caledonia. It is often considered the sister to all other living flowering plants.
2. Nymphaea (Water Lilies): A member of the Nymphaeales, known for their aquatic
habitat and simple floral structures, which retain many ancestral features.
3. Austrobaileya scandens: A representative of the Austrobaileyales, found in tropical
rainforests, with large, simple flowers and primitive features like spiral floral
arrangements.


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