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The angiosperms. Greek: angeion case; sperma seed. By far the most diverse group of plants that has ever existed with more than 240,000 different species. Why are there so many species. Angiosperms. Time scale. Origin of angiosperms. Mosses. Ferns .

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the angiosperms
The angiosperms

Greek: angeion case; sperma seed

By far the most diverse group of plants that has ever existed with more than 240,000 different species.

why are there so many species
Why are there so many species


Time scale

Origin of angiosperms



Why are there so many species?


Angiosperms probably originated in the tropics

West Gondwana, equivalent to modern South America plus Africa


principal differences between gymnosperms and angiosperms
Principal differences between Gymnosperms and Angiosperms

1. Leaves have finely divided venation

2. Xylem contains vessels as well as tracheids and parenchyma

3. Phloem contains sieve elements with companion cells

4. Ovules protected within an enclosed structure

5. Double fertilization to produce diploid zygote and triploid endosperm nucleus

6. Generally hermaphrodite flowers and cross pollinating (70%)

monocotyledons and dicotyledons
Monocotyledons and Dicotyledons



Triticum, wheat

Zea mays corn


Oak trees, Quercus


Lycopersicon, tomato

Potato, Solanum tuberosum

angio gymno 1 leaves have finely divided venation
Angio-Gymno 1. Leaves have finely divided venation

Coleus leaf cleared of cell contents and with xylem stained

A dicotyledon

Typically veins are distributed such that mesophyll cells are close to is a vein.

The network of veins also provides a supportive framework for the leaf.

leaf of a monocotyledon plant
Leaf of a monocotyledon plant

The major venation follows the long axis of the leaf and there are numerous joining cross veins so that, as with the dicotyledon, mesophyll cells are always close to a vein.

tomato leaf
Tomato leaf

Upper epidermis

Pallisade parenchyma: chloroplasts visible around cell periphery

Longitudinal section through a vascular bundle

Xylem vessel: annular thickening around cell wall


Bundle Sheath

Spongy parenchyma

Lower epidermis

ficus leaf
Ficus leaf

Ficus, the fig, is a xerophyte

Collenchyma forming a hypodermis

Pallisade parenchyma

Spongy parenchyma

Vascular bundle

Collenchyma above and below the vascular bundle

Lower epidermis

leaf cross section of bouteloua
Leaf cross section of Bouteloua

Upper epidermis

Bulliform cells



Parenchyma with chloroplasts

Lower epidermis

Bundle sheath cells with chloroplasts


Sclerified fibers

leaf cross section of zea mays corn
Leaf cross section of Zea mays ("corn").

Upper epidermis

Bulliform cells


Bundle sheath cells with chloroplasts

Parenchyma with chloroplasts

Lower epidermis


anatomical separation of the c4 photosynthesis component processes
Anatomical separation of the C4 photosynthesis component processes

Parenchyma filled with chloroplasts

Bundle sheath cells filled with chloroplasts. CALVIN REACTION SITE



Carbon skeleton compounds return to parenchyma

C4 acids synthesized in the parenchyma move to the bundle sheath


Ways in which Angiosperms are different from Gymnosperms

Angio-Gymno 2. Xylem contains vessels as well as tracheids and parenchyma

Angio-Gymno 3. Phloem contains sieve elements with companion cells

angiosperm xylem and phloem
Angiosperm xylem and phloem

In Angiosperms Xylem and Phloem contain more specialized cells than in Gymnosperms as well as containing Fibers and Parenchyma.

Xylem: Vessel Elements

Phloem: Sieve elements, Companion cells


Tracheids provide better support but less slower rates of water conduction than vessels



Wide vessel element: This kind of cell is better for fluid conduction than physical support.

A vessel is composed of several vessel elements

These vessel elements have completely perforated end walls

Elongated vessel element: This cell provides moderate support and fluid conduction.

Tracheids lack perforation plates but their end walls contain numerous pits.


Companion Cells (CC)

Sieve Tube Members (STM)

Cucurbita phloem


Sieve plate

STMs and CCs develop from the same progenitor cell. STMs, are columnar cells and unite vertically to form a Sieve Tube. STMs have no nucleus at maturity and depend on CC to regulate physiological processes. Each STM has one to several CC. The Sieve Plate is analogous to a Perforation Plate in vessels.

dicotyledon stem cross section
Dicotyledon stem cross section

J. D. Mauseth

Angelica stem transverse section is typical of a dicotyledon plant without secondary thickening.

Stems as diverse as slender vines, fat cacti, or as modified as potato tubers all have this organization, but with various zones modified. Cacti are so wide because they have an exceptionally thick cortex. Potato tubers have a gigantic pith and almost no wood.

Four zones:

1) epidermis

2) cortex, in many species the outermost part is a hypodermis

3) ring of vascular tissues, usually a ring of vascular bundles

4) pith.

We eat Angelica in confectionary

transverse section of corn stem zea mays
Transverse section of corn stem, Zea mays.

Transverse section of corn stem, Zea mays.

This is the organization of monocot stems: numerous vascular bundles distributed throughout a tissue that may be either parenchyma or collenchyma

Vascular bundles

There are four parts:

1) epidermis

2) cortex with or without part differentiated into a hypodermis

3) vascular bundles

4) a matrix of parenchyma called conjunctive tissue or pith

sections you need to have read
Sections you need to have read

17.10, 31.2 through 31.6

Courses that deal with this topic

Botany 443 Origins of our modern floras