[PDF] Embryology in Relation to Angiosperms Taxonomy | 7 Role of Embryology in Taxonomy

Embryology in Relation to Angiosperms Taxonomy

Embryology, the study of an organism’s developmental processes from fertilization to birth, provides invaluable insights into the relationships and classifications of angiosperms. By investigating distinct embryological features, taxonomists can uncover unique characteristics that aid in identifying and grouping plant species.

Several angiosperm families are marked by these distinctive embryological traits, offering a window into their evolutionary history and relationships. These features have proven to be a powerful tool in understanding the complexities of angiosperm taxonomy.

Families Marked Out by Embryology in Relation to Angiosperms Taxonomy :

In the field of angiosperm taxonomy, specific families are often characterized by unique embryological features that are consistently found among all members. These distinctive embryological traits are crucial in classifying and understanding the relationships between different angiosperm taxa. Several families stand out due to these specific embryological characteristics:

Podostemaceae

The Podostemaceae family encompasses perennial aquatic herbs. An exceptional feature within this family is the formation of a pseudoembryo sac resulting from the disintegration of nucellar tissue during embryogenesis. Notably, Podostemaceae shares other common embryological attributes, such as pollen grains occurring in pairs, bitegmic tenuinucellate ovules, bisporic embryo sacs, a solanad type of embryogeny, prominent suspensor haustoria, and the absence of triple fusion, consequently leading to the absence of endosperm. This is an important example of Role of Embryology in Taxonomy.

Cyperaceae

The distinctive characteristic of Cyperaceae lies in the formation of only one microspore per microspore mother cell. Following meiosis, one of the four microspore nuclei gives rise to a pollen grain. This differs from Epacridaceae, where the degeneration of three microspore nuclei is observed. An additional contrast is the timing of pollen shedding – Cyperaceae releases pollen at the 3-celled stage, while Epacridaceae sheds pollen at the 2-celled stage.

Onagraceae

Family Onagraceae stands apart due to its possession of an Oenothera type of embryo sac, a feature unique to this family. This particular embryo sac consists of four nuclei and originates from the micropylar megaspore of the formed tetrad. Notably, this embryo sac type is not found in any other family except as an anomaly.

Specific Examples of Embryology in Relation to Angiosperms Taxonomy:

Embryological data have proven highly valuable in determining taxonomic relationships within angiosperms. Several examples illustrate how embryology aids in the interpretation of taxonomic affinities:

Trapa

Initially placed within the family Onagraceae, the genus Trapa was moved to the family Trapaceae based on distinct aquatic habits, leaf types, and other morphological features. Embryological features supported this separation, including pyramidal pollen grains, semi-inferior bilocular ovaries with single ovules, Polygonum-type embryo sacs, absence of endosperm, Solanad-type embryos, and unique fruit characteristics.

Paeonia

Genus Paeonia was initially classified under the family Ranunculaceae but was later recognized as a distinct family, Paeoniaceae. Embryological features such as centrifugal stamens, pollen characteristics, unique embryo development, and arillate seeds provided compelling evidence for its reclassification into its own family.

Exocarpos

The genus Exocarpos, previously considered for relocation to Gymnosperms, remained firmly within the angiosperm family Santalaceae based on detailed embryological analysis. Characteristics such as endothecium in anthers, 2-celled pollen shedding, Polygonum-type embryo sacs, and cellular endosperm reinforced its placement within Santalaceae.

Loranthaceae

In the family Loranthaceae, distinct embryological features led to the separation of its subfamilies. Triradiate pollen grains, specific embryo sac types, embryogeny patterns, and other characteristics differentiated Loranthoideae from Viscoideae. Influential taxonomists supported this separation and is widely acknowledged in modern classification systems.

Let’s Summarise all the significant points here in the table:

Family	Distinct Embryological Features	Taxonomic Significance
Podostemaceae	1. Formation of pseudo embryo sac due to nucellar tissue disintegration 2. Occurrence of pollen grains in pairs 3.Bitegmic tenuinucellate ovules 4. Bisporic embryo sac 5. Solanad-type embryogeny 6. Prominent suspensor haustoria 7. Absence of triple fusion and endosperm	These unique embryological features help classify members of the Podostemaceae family and differentiate them from other angiosperms.
Cyperaceae	1. Formation of only one microspore per microspore mother cell 2. Shedding of pollen at the 3-celled stage	The distinct embryological feature of single microspore formation and the timing of pollen shedding set Cyperaceae apart from other related taxa, like Epacridaceae.
Onagraceae	1. Presence of Oenothera type of embryo sac (4-nucleate 2. Unique embryo sac derived from micropylar megaspore of tetrad	The Oenothera type of embryo sac is exclusive to the Onagraceae family. This unique feature aids in identifying and classifying members of this family.
Trapa	1. Pyramidal pollen grains with 3 folded crests 2. Semi-inferior, bilocular ovary with a single ovule in each loculus 3. Polygonum type of embryo sac 4. Absence of endosperm 5. Solanad-type embryo 6. Extremely reduced cotyledon 7. Large, one-seeded drupe fruit	Embryological features align with other morphological traits, reinforcing the placement of Trapa within the Trapaceae family.
Paeonia	1. Centrifugal stamens 2. Reticulately-pitted exine with large generative cells in pollen 3. Unique embryogeny with coenocytic stage 4. Seed arillate	Embryological attributes support the distinct classification of Paeonia within the Paeoniaceae family, validating its separation from its previous placement under Ranunculaceae.
Exocarpos	1. Angiospermous characteristics in flower and anther structure 2. 2-celled pollen shedding 3. Polygonum-type embryo sac 4. Cellular endosperm	Embryological analysis solidifies the placement of Exocarpos within the angiosperm family Santalaceae, rejecting the suggestion of its inclusion in the Gymnosperms.
Loranthaceae	1. Triradiate pollen grains in Loranthoideae, spherical pollen grains in Viscoideae 2. Embryo sac types and embryogeny patterns differ between subfamilies	Embryological variations between Loranthoideae and Viscoideae subfamilies support the separation of Loranthaceae into distinct families, Loranthaceae and Viscaceae, enhancing the accuracy of their taxonomic placement.

In conclusion, the intricate study of embryology in angiosperms reveals a wealth of information crucial for taxonomy. The distinct embryological features observed within various families act as markers, helping taxonomists delineate relationships and make informed classifications. By delving into the developmental intricacies of these plants, we uncover a deeper understanding of their evolutionary pathways and connections, ultimately enriching our comprehension of the diverse world of angiosperms.

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