Comparative account of various systems of Angiosperm Classiification

The Bentham and Hooker system of classification, also known as the "Bentham and Hooker's system," was proposed by George Bentham and Joseph Dalton Hooker in their book "Genera Plantarum" published in 1862-1883. It was one of the earliest comprehensive classifications of angiosperms. The system primarily focused on the morphological characteristics of plants, including vegetative and floral features. Here are the key features and divisions of the Bentham and Hooker system:

1. Subdivision into Monocotyledons and Dicotyledons:

   The Bentham and Hooker system recognized two major classes of angiosperms: Monocotyledons (Monocots) and Dicotyledons (Dicots). This division was based on the number of cotyledons (seed leaves) present in the embryo.

2. Monocotyledons:

   Monocotyledons were characterized by having seeds with a single cotyledon, parallel-veined leaves, flower parts in multiples of three, and scattered vascular bundles in the stem. The Monocot class was further divided into a series of orders, families, genera, and species.

3. Dicotyledons:

   Dicotyledons had seeds with two cotyledons, net-veined leaves, flower parts in multiples of four or five, and a ring-like arrangement of vascular bundles in the stem. The Dicot class was also divided into numerous orders, families, genera, and species.

4. Hierarchical classification:

   The Bentham and Hooker system employed a hierarchical approach to classification. It organized plants into progressively smaller taxonomic units. The major taxonomic categories included subclasses, orders, families, genera, and species.

5. Emphasis on floral characters:

   Floral characteristics, such as the number and arrangement of floral organs (sepals, petals, stamens, and carpels), played a significant role in the Bentham and Hooker system. The system considered the diversity of floral structures in determining relationships between different groups of plants.

6. Genera Plantarum:

   The culmination of the Bentham and Hooker system was their monumental work "Genera Plantarum." It provided a comprehensive account of plant genera known at that time, classified within their respective families and orders. This work was a valuable resource for botanists and served as a foundation for subsequent angiosperm classifications.

The Bentham and Hooker system laid the groundwork for future classifications and was widely used during its time. However, with advancements in molecular biology and our understanding of evolutionary relationships, more modern classification systems, such as the APG system, have replaced the Bentham and Hooker system as our knowledge of angiosperms has expanded.

The Engler and Prantl system of classification, also known as the "Engler and Prantl's system" or the "Natural System," was proposed by Adolf Engler and Karl Anton Eugen Prantl. It was published in their work "Die natürlichen Pflanzenfamilien" (The Natural Plant Families) between 1887 and 1915. The Engler and Prantl system aimed to classify angiosperms based on their evolutionary relationships and phylogenetic patterns. Here are the key features and divisions of the Engler and Prantl system:

1. Subdivision into subclasses and superorders:

   The Engler and Prantl system recognized two major subclasses of angiosperms: the Dicotyledonae (Dicots) and the Monocotyledonae (Monocots). Each subclass was further divided into superorders, which represented major lineages within the respective subclasses.

2. Superorders and orders:

   The superorders in the Engler and Prantl system represented major evolutionary groups within the subclasses. They were further divided into orders, which encompassed smaller groups of related families. The orders were based on shared morphological and anatomical characteristics.

3. Families:

   Families were considered the fundamental units of the Engler and Prantl system. They were grouped within orders based on similarities in their vegetative and reproductive structures. Each family consisted of one or more genera, which shared common characteristics.

4. Genera and species:

   Genera were categorized within families based on their morphological and anatomical affinities. Genera represented groups of closely related species. Species, the most specific taxonomic category, were defined by distinct morphological characteristics and reproductive compatibility.

5. Emphasis on morphological features:

   The Engler and Prantl system heavily relied on morphological characters to establish evolutionary relationships. These characters included floral structure, inflorescence type, leaf characteristics, stem anatomy, and other vegetative features. The system aimed to capture the diversity and evolutionary trends in angiosperms through the examination of these traits.

6. Evolutionary relationships:

   The Engler and Prantl system attempted to reflect the evolutionary history of angiosperms by organizing taxa into groups that represented their phylogenetic relationships. It aimed to arrange plant groups in a manner that reflected their shared ancestry and common evolutionary developments.

The Engler and Prantl system was highly influential and widely used during the late 19th and early 20th centuries. It provided a comprehensive overview of angiosperm diversity and attempted to depict their evolutionary relationships based on morphological characteristics. However, with advancements in molecular biology and our understanding of plant evolution, more modern systems, such as the APG system, have provided a more accurate and phylogeny-based classification of angiosperms.

The Cronquist system of classification, proposed by Arthur Cronquist in 1968, was a widely accepted and influential system for classifying flowering plants (angiosperms). The system aimed to provide a practical and comprehensive classification scheme based on a combination of morphological and anatomical characteristics. The Cronquist system underwent several revisions and refinements over the years. Here are the key features and divisions of the Cronquist system:

1. Division into two classes:

   The Cronquist system recognized two main classes of angiosperms: Magnoliopsida (dicotyledons) and Liliopsida (monocotyledons). This division was primarily based on the number of cotyledons (seed leaves) in the embryo.

2. Subclasses and superorders:

   Each class was further divided into subclasses, which represented major lineages within the respective classes. The subclasses were further subdivided into superorders, which represented major evolutionary groups.

3. Orders and families:

   Orders were the next hierarchical level in the Cronquist system. Each order encompassed a group of related families. Orders were defined based on shared morphological and anatomical characteristics.

4. Families and genera:

   Families were considered fundamental units in the Cronquist system. Each family consisted of one or more genera, which shared common morphological features. Families were defined by a combination of floral and vegetative characteristics.

5. Emphasis on floral features:

   The Cronquist system heavily relied on floral characters, such as the number and arrangement of floral organs (sepals, petals, stamens, and carpels), to determine relationships and classify angiosperms. Floral characteristics were considered essential for identifying and grouping plants into families and higher taxa.

6. Hierarchy and rank:

   The Cronquist system followed a hierarchical arrangement of taxa, with each level representing a progressively smaller taxonomic unit. The system used a standardized set of ranks, including division, class, subclass, superorder, order, family, genus, and species.

The Cronquist system was widely used and had a significant impact on plant taxonomy for several decades. It provided a practical framework for identifying and classifying flowering plants based on readily observable morphological features. However, with the advent of molecular phylogenetic studies and advancements in DNA sequencing techniques, it became clear that the Cronquist system did not always reflect the true evolutionary relationships among plants. As a result, more modern classification systems, such as the Angiosperm Phylogeny Group (APG) system, have been developed to incorporate molecular data and provide a more accurate depiction of angiosperm relationships.

The APG system, or the Angiosperm Phylogeny Group system, is a series of classification systems developed by an international group of botanists to reflect the evolutionary relationships among angiosperms (flowering plants) based on molecular data. The APG system represents a significant shift from traditional classification systems that relied primarily on morphological characteristics. Here are the key features and developments of the APG system:

1. APG (1998):

   The first APG system was published in 1998 and marked a major departure from previous classification systems. It was based on DNA sequence data, particularly from the chloroplast gene rbcL. The system emphasized the use of monophyletic groups (clades) to represent common ancestry.

2. APG II (2003):

   The APG II system, published in 2003, built upon the initial APG system and incorporated additional molecular data, including nuclear genes. It expanded the phylogenetic framework and introduced many changes in the classification. Notably, it recognized several major clades, such as the magnoliids and the monocots.

3. APG III (2009):

   The APG III system, published in 2009, further refined the classification and incorporated more extensive molecular data from multiple gene regions. It introduced changes in family circumscriptions and recognized additional clades, including the eudicots, which became the largest group of flowering plants.

4. APG IV (2016):

   The APG IV system, published in 2016, represents the most recent and widely accepted version of the APG system. It incorporated additional molecular data from diverse plant lineages and refined the classification further. The APG IV system recognizes numerous major clades and provides a more comprehensive understanding of angiosperm relationships.

The APG system does not use traditional taxonomic ranks like classes, orders, and families. Instead, it focuses on clades, which represent monophyletic groups comprising an ancestor and all of its descendants. The APG system also recognizes the importance of ongoing research and new data, allowing for revisions and updates as our understanding of angiosperm phylogeny improves.

It's important to note that the APG system represents a dynamic field of research, and there may be future iterations and refinements as new data and analytical techniques emerge. The APG systems have significantly enhanced our understanding of angiosperm relationships and continue to serve as a valuable tool for plant classification and evolutionary studies.