Angiosperms – the flowering plants.
Flowering plants appear to have emerged between 180-140 million years ago (mya) and have an unknown common ancestor.
They are thought to be a sister group to the gymnosperms.
Shared features of the angiosperms include:
- a perianth (sepals and petals)
- fruits with fleshy endosperm to nourish the seed.
- double fertilisation.
- ovules enclosed within an ovary,
- stamens with two pairs of pollen sacs.
The flowering plants were initially divided into groups based only on appearance.
The introduction of microscopy added a great deal of information and now newer techniques such as chemical tests and DNA
analysis are helping formulate a definitive classification.
The aim is to sort all flowering plants into groups with each member having the same common ancestor and to try and resolve the
relationships between the groups.
There is now broad agreement on this and current thinking is summarised in the Angiosperm Phylogeny Group’s classification.
The latest major version, the AGP4, was released in 2016 and there have been some updates to it since.
Some publications still flowering plants into the dicots, monocots and eudicots although the term ‘dicot’ has largely been abandoned.
On my original website (brisbanebotanyplus.com) I divided them into the following groups:
- Basal angiosperms.
- Early Eudicots (called Basal eudicots by some).
- Core Eudicots.
This was a bit complex and I abandoned it on the current site which has them divided by family.
These divisions are still in common usage so a brief summary of them, and others used by the APG, are given below.
These are the most primitive flowering plants – the first to diverge from the unknown common ancestor.
It is a small group of about 200 species in three unrelated orders.
The Amborellales were the earliest followed by the Nymphaeales and the Austrobaileyales.
The basal angiosperms have a number of features in common including:
- A perianth undifferentiated into petals and sepals (tepals).
- Carpels separate.
- Leaves alternate and spirally arranged.
- 2 seed leaves.
- Pollen grains with one aperture.
Apertures are special areas (pores and grooves) on the wall of a pollen grain that
may have various functions.
The basal angiosperms make up less than 5% of all plant species.
The next separate lineage to branch off was the Chloranthales then the Magnoliid clade possibly derived from the Chloranthales.
- They have flowers with parts in 3’s,
- leaf veins that usually branch and
- pollen with 1 aperture.
There are about 9,000 species in the Magnoliales, Piperales, Canellales and Laurales orders.
The Monocots are all descended from a single unknown common ancestor.
They are closely related to the Ceratophyllales, Chloranthales and the Magnoliids but it is uncertain how.
They may have emerged before or after the Magnoliids.
There are a number of features which tie the monocots together including:
- Only 1 seed leaf or cotyledon.
- Pollen grains have only one aperture.
- Flower parts mostly in 3’s usually with a perianth of 6 tepals.
- Many fibrous roots growing from the base of the stem rather than a tap root with side branches.
- Fused carpels.
- Leaves mostly have parallel veins either straight, curved or penni-parallel (penniveined).
- Simple connections between veins, not a reticular network.
- Vascular bundles are mostly scattered or occasionally in 2 rings rather than just 1 ring.
They are a large group of 60,000 to 70,000 plants – about 23% of flowering plants.
The Ceratophylales about 6 species of aquatic plants.
The Early Eudicots.
The eudicots appeared about 125 million years ago just after the earliest or basal angiosperms.
This group have:
- A variable perianth with parts in 3’s, 4’s or undifferentiated.
- Pollen with 3 apertures.
- Separate carpels.
- Many stamens.
Orders are the Ceratophyllales, Ranunculales, Proteales, Trochodendrales and the Buxales.
They comprise less than 5% of angiosperms.
The Core Eudicots.
There are about 190,000 species which is over 70% of all angiosperms.
Being such a large group they show an enormous range of variation in habit, appearance, chemistry, geographic distribution etc.
Characteristics of the group include:
- Pollen grains with 3 (or more) apertures or pores.
- 2 seed leaves.
- Flower parts in 4’s or 5’s.
- Leaf veins that usually branch.
- Flower parts can be fused to each other.
- Perianth differentiated into sepals and petals.
- Stamens with 2 pairs of pollen sacs.
The AGPIII classification lists 413 families.
Families with the largest number of species include the Asteraceae or Compositae with 22,750
daisy species and Fabaceae or Leguminosae with 19,400 bean and pea species.
Because Plants will be the largest section there is a ‘Flowering Plant Index’ for them.
It contains the scientific and common names, which of the 4 sections they are in and the family.
Entries are not hyperlinked but just a guide on where to look.
It is on the left side menu.