SEED PLANTS: ANGIOSPERMS
First land plants appeared probably in the late Ordovician about 450 million years ago.
Rhynia appeared in the mid-Silurian record about 425 million years ago.
Trimerophytes first appeared in the early Devonian about 395 million years ago.
Ferns, lycopods, sphenophytes and progymnosperms proliferated in the late Devonian and
Carboniferous, 380 to about 280 million years ago.
Gymnosperms diversified during the Mesozoic, 250 to 65 million years ago.
Angiosperms first appeared about 130 million years ago in the early Cretaceous.
ORIGIN AND DIVERSIFICATION OF THE ANGIOSPERMS
Unique characteristics of the angiosperms are:
1.
2.
3.
4.
5.
6.
7.
Flower
Close carpels.
Double fertilization producing endosperm and embryo.
Three-nucleate microgametophyte.
Eight-nucleate magagametophyte.
Stamens with pairs of pollen sacs.
Presence of sieve tubes and companion cells in phloem.
All angiosperms probably arose from a common ancestor. They are monophyletic.
The earliest known angiosperm fossils are from the early Cretaceous about 132 million years ago.
Molecular data estimates the origin of the angiosperms to be 180 to 140 million years ago, in the
Jurassic (~201 to 145 mya).

Molecular data tends to overestimate the age of organisms (Rodrìguez-Trelles,
F., R. Tarrìo, and F. J. Ayala. 2002.)
Eudicots diversified rapidly during the middle of the Cretaceous.
Early eudicots probably had small, simple flowers, with sepals and petals not clearly
differentiated.
By the end of the Cretaceous several orders of angiosperms were already in existence and
dominated the flora of the Northern Hemisphere.
Adaptive traits that made them resistant to cold and drought:
1. Small, tough leaves.
2. Vessels elements.
3. Resistant seed coat.
4. Deciduous habit.
These traits are not unique to angiosperms but the combination of traits made them successful.
Other traits that probably helped in their struggle for dominance were
1.
2.
3.
4.
Development of sieve tube members with companion cells.
System of pollination.
Mechanisms of seed dispersal.
Chemical defense.
About 130 million years ago, when angiosperms first appeared, Africa, South America, India,
Antarctica and Australia were still connected in the great southern continent Gondwanaland
90 million years ago India began to separate from Africa and Antarctica, and Africa and South
America had completed their separation.
India moved northward and collided with Southern Asia about 65 million years ago creating the
Himalayas and the Tibetan plateau.
Australia and Antarctica remained together until about 55 million years ago when they began to
drift apart.
In the central regions of Western Gondwanaland (Africa and South America) the climate was arid
to subhumid, which might have challenged plants to produce new forms.
Later on climates became milder and magnoliids have survived in these milder climates ever
since.
There are older fossils that may represent groups with some but not all the characteristics of the
angiosperms.
Ancient angiosperms had pollen with one aperture.
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Monocots, cycads, ginkgo and other groups have this kind of pollen.
One aperture pollen is considered to be ancestral and primitive.
There is an active debate about what the earliest angiosperms were like -- trees similar to
Magnolia or diminutive herbaceous plants -- the Paleoherbs.
The
most
obvious
characteristic
angiosperm is
The classification
based on the structure
distinguishing
The flower contains the
The name angiosperm is
vessel, and sperma means seed.
of an
the flower.
of Angiosperms is
of the flower, its
characteristic.
reproductive parts of the plant.
derived from the Greek angeion, means
Angiosperms are divided into two classes, the Dicots (Magnoliopsida) and the Monocots
(Liliopsida).
“In 1682, John Ray published his Methodus Plantarum Nova, in which Dicotyledones and
Monocotyledones were first given formal taxonomic standing. This system was popularized by the French
botanist Antoine Laurent de Jussieu in his Genera Plantarum of 1789, a work which improved upon, and
gradually replaced, the system of plant classification devised by Linnaeus.”
http://www.ucmp.berkeley.edu/glossary/gloss8/monocotdicot.html
The paleoherbs are a small group of flowering plants which have traditionally been classified as
dicots, but which have many characters in common with monocots.
“Even after the general acceptance of Monocots and Dicots as the primary groups of flowering plants,
botanists did not always agree upon the placement of families into one or the other class. Even in this
century some plants called paleoherbs have left problems for taxonomy of angiosperms. These plants have
a mix of characters, which do not occur together in most other flowering plants. For instance, the
Nymphaeales, or water lilies, have reticulate venation in their leaves, and what may be a single cotyledon
in the embryo. It is not clear whether it is a single lobed cotyledon, or two, which have been fused. The
water lilies also have a vascular arrangement in their stem similar to that of monocots.
There are also monocots which posses characters more typical of dicots. The Dioscoreales and
Smilacaceae have broad reticulate-veined leaves; the Alismataceae have acropetal leaf development; and
Potamogeton is one of several monocots to have floral parts in multiples of four.”
http://www.ucmp.berkeley.edu/glossary/gloss8/monocotdicot.html
True dicots are called eudicots.
DIVISION MAGNOLIOPHYTA
There are about 235,000 species of angiosperms.
It is the largest and most diverse group of photosynthetic organisms.
Angiosperms are heterosporangiate, producing pollen and ovules in different organs.
The pollen and ovule-bearing organs are usually produced together in a bisporangiate strobilus
called a flower.
Angiosperms differ from other seed plants in that they enclose their ovules (and seeds) within a
carpel.
Other unique features of the angiosperms are the production of fruits and distinctive life-cycle
features.
There are about 200 species of parasitic monocots and 2800 species of parasitic eudicots.
Most angiosperms are free living, but there are a few saprophytic and parasitic species.
Unique characteristics of the angiosperms are:
8.
9.
10.
11.
12.
13.
14.
15.
Flower
Close carpels.
Double fertilization producing endosperm and embryo.
Three-nucleate microgametophyte.
Eight-nucleate magagametophyte.
Stamens with pairs of pollen sacs.
Presence of sieve tubes and companion cells in phloem.
Presence of vessels in the xylem.