Dicta of Evolution

Kingdom: ………….., divided into divisions
Division: ……………., divided into classes
Class: ……………………, divided into orders
Order: …………………., divided into families
Family: …………………., divided into genera
Genus : …………………., divided into species
Species:…………………The smallest taxon.

The classification of plants
• Results in an organized system for the naming and
cataloging of future specimens.
• Reflects scientific ideas about plant inter-relationships.
• Provides a convenient method of plant identification.
• Detects and reconstructs the evolutionary history of the
plant kingdom.
• Provides an integration of all available information.

Theophrastus (370 -285 B.C.), a Greek botanist,
known as the father of botany considered habit as an
essential character.
classified plants into
4 groups on the basis
of their habits:-
herbs --> subshrubs -->
shrubs -->trees.
and separated according to flowering and non-
flowering.

Albertus Magnus
(German - 1200-1280
A.D.) produced a
classification system
that recognized - for
the first time
monocots and dicots.

Carl Linnaeus (1707-1778) Swedish
taxonomist - known as the father of
taxonomy, in his book Species
Plantarum 1753, he created
a sexual system of
classification that divided plants
into 24 classes based on the
number, union, and length of
stamens. Secondary grouping with
these classes (Order) was based on
the gynoecium (mostly the number
of styles).

George Bentham (1800-1884) and Sir Joseph D. Hooker
(1817-1911), in Genera Plantarum (1862-1883), recognized
97,205 species belonging to 7,569 genera of families of
flowering plants. The seed plants or Phanerogams were
divided into three classes – Class I: Dicotyledons, Class II:
Gymnosperms and Class III: Monocotyledons.

Adolf Engler (1844-1930) and Karl Prantl (1849-1893):
• Families arranged based on the complexity of floral
morphology.
• The Plant Kingdom is divided into 14 major divisions.
• Proposed unisexual flowers --primitive
• (simple = primitive)
• Monocots were considered to be primitive.

 Charles Edwin Bessey (1845-1915), American, published
‘The Phylogenetic Taxonomy of Flowering Plants’ (1915).
Plants
Primitive Plants Advanced Plants
Example:
Unisexual flowers
Example:
Bisexual flowers

 John Hutchinson (1884-1972) proposed a radical revision of
the angiosperm classification system devised by Hooker and
by Engler and Prantl that had become widely accepted
during the 20th
C.
 Hutchinson system suggested 2 main divisions of
Angiosperms: herbaceous and woody.

 Arthur John Cronquist (1919–1992) was a North American
botanist and a specialist in Compositae plants.
 Cronquist System was an expansion and a modification of
Bessey’s System.
 The Cronquist system divides flowering plants into 2 groups:
Magnoliopsida (Dicots) and Liliopsida (Monocots).

 The 'Takhtajan System’ (1997) treats flowering plants as a
division (phylum), Magnoliophyta, with two classes,
Magnoliopsida (dicots) and Liliopsida (monocots).
 These two classes are subdivided into subclasses, and then super-
orders, orders, and families.
 Thorne system (1992) used the name
Magnoliopsida for the flowering plants
(Angiosperms). It counts 69 orders, 437 families.

 Angiosperms Phylogeny Group
(APG): Molecular-based system
of plant taxonomy. The system
was published by the Angiosperm
Phylogeny Group in 1998.
2: .
Q: write a brief about one of the pioneers of plant taxonomy and
his contribution in this field.

• Bessey's system was based on a series of "dicta" or
statements of the guiding principles that be used in
determining the degree of primitiveness or evolutionary
advancement of a plant group.
1. Evolution is not always upward, but often it involves degradation
and degeneration.
2. In general, homogeneous structures (with many and similar parts)
are lower, and heterogeneous structures (with fewer and
dissimilar parts) are higher

3. Evolution does not necessarily involve all organs of the plant
equally in any particular period, and one organ may be advancing
while another is retrograding.
4. Upward development is sometimes through an increase in
complexity, and sometimes by a simplification of an organ.
5. Evolution has generally been consistent, and when a particular
progression or retrogression has set in, it is persisted in to the
end of the phylum.
6. The holophytic (chlorophyll-green) plants precede the colorless
(hysterophytic) plants, and the latter are derived from the
former.
7. Plant relationships are up and down the genetic lines, and must
constitute the framework of phylogenetic taxonomy.

8. The stem structure with collateral vascular
bundles arranged in a cylinder is more
primitive than that with scattered bundles
and the latter are to be regarded as
derived from the former.
9. Woody stems (as of trees) are more
primitive than herbaceous stems, and
herbs are held to have been derived from
trees.
10. The simple, unbranched stem is an earlier
type, from which branching stems have
been derived.

11. The arrangement of leaves in pairs on the
stem is held to have preceded the spiral
arrangement in which the leaves are
solitary at the nodes.
12. Simple leaves preceded branched
("compound") leaves.
13. Historically leaves were first persistent
("evergreen") and later deciduous.
14. The reticulated venation of leaves is the
normal structure, and the parallel venation
of some leaves is a special modification
derived from it.

16. Polycarpy is the earlier condition, and
oligocarpy was derived from it later.
17. In earlier (primitive) flowers there are
many stamens (polystemonous) while in
later flowers there are fewer stamens
(oligostemonous).
15. The polymerous flower structure precedes, and the
oligomerous (Having only a few members in a particular organ)
structure follows from it, and this is accompanied by a
progressive sterilization of sporophylls.

18. The apochlamydeous perianth is earlier
and the gamochlamydeous perianth is
derived from it by symphysis of the
members of perianth whorls.
19. Apocarpy is the primitive structure, and
from it syncarpy was derived later.
20. The stamens of primitive flowers are
separate (apostemonous), while those of
derived flowers are often united
(synstemonous).
21. Hypogyny is the more primitive
structure, and from it epigyny was derived
later.

22. The endospermous seed is primitive
and lower, while the seed without
endosperm is derived and higher.
23. Consequently, the seed with a small
embryo (in endosperm) is more
primitive than the seed with a large
embryo (in scanty or no endosperm).
24. Petaly is the normal perianth structure,
and apetaly is the result of perianth
reduction (aphanisis).

25. Actinomorphy is an earlier structure than
zygomorphy, the latter results from a
change from similar to a dissimilar growth
of the perianth whorls.
26. The powdery pollen is more primitive
than that with coherent or massed pollen.
27. Flowers with both stamens and carpels
(monoclinous) precede those in which
these occur on separate flowers
(diclinous).
28. In diclinous plants the monoecious
condition is the earlier, and the dioecious
later.

1. Orthodox Criteria
a-The macro-morphological characters
• Include the characters of the root system and other underground
parts (rhizome, tuber, bulb). The macro-morphological characters
of the aerial parts include the characters of stem, leaf, flower,
inflorescence, fruit... etc.
b- The Micro-morphological Characters
• The anatomical characters of the vegetative structures have been
of importance in separating higher categories, such as
gymnosperms from angiosperms and monocot from dicot.

2. Palynological Criteria
Palynology is the study of pollen grains and spores including pollen
morphology such as: Composition of pollen grains, Exine
sculpture, Number, position of apertures, Shape of pollen.
3. Chemotaxonomy Criteria
Plant Chemotaxonomy is the application of chemical data to
systematic problems.
4. Embryology Criteria
The embryological characters of taxonomic value include the
anther; development of the pollen grains and the ovule;
megasporogenesis and development of the embryosac;
fertilization; endosperm; embryo and seed coat.

5. Cytology
The utilization of the characters and phenomena of cytology for the
explanation of taxonomic problems is referred as cytotaxonomy.
6. Molecular Systematics
The molecular analyses of the three angiosperm genomes: (cp
DMA), (mt DNA) and (n DNA) are applicable to the study of
phylogenetic and taxonomic relationships.
7- Physiological Criteria
Plants show differences in their metabolic process and chemical
reaction. On this basis, similarities and differences can be
established amongst the plants.

Dicta of Evolution

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