Pflanzen Peter Morrell
Flowering Plants or Angiospermae [phylum]
are the dominant plants on earth at this time and have been for the last 100
million years. Traditionally they have been divided into two divisions
[classes]
called Monocotyledons [one
seed-leaf] and Dicotyledons [2 seed leaves] based on the number of food stores
contained in the seeds. Monocots also have parallel venation while the others
have complex netted venation.
Apart from some other structural
features of importance, the classification of Angiosperms rests mostly upon the
structure of the flower, which is undoubtedly their most distinctive feature.
This is
mainly because it is the flower
which shows such remarkable plasticity of form. This variability of the
structure of the flower in turn reflects the intimate adaptive association of
flowers with insects,
whose evolution they have closely
paralleled. Indeed, such a phenomenon is often given as an example of
co-evolution because of the strength and longevity of the contact between the 2
groups, and
the diverse ways they have mutually
influenced each other in structure and in life-cycles.
"During the first 70 million years
of angiospermous evolution all the known flowers were radially symmetrical. It
is only in the Tertiary (66.4 to 1.6 million years ago) during the late
Paleocene
and early Eocene (63.6 to 52 million
years ago) that the first evidence of bilaterally symmetrical flowers is found.
The evolution of bilateral flowers, as, for example, those of the legumes and
orchids,
is an adaptation for specialized
pollinators such as social insects (bees) and some birds. The sterile organs
(sepals, petals) are modified to present a certain flower orientation to the
pollinator, enabling
the pollinator to enter the flower
where the pollen organs and pollen-receptive tissue are positioned to maximize
effective pollination. During the early Tertiary, the bilateral organization of
floral organs coevolved with animal behaviour independently at different times
and in various groups of angiosperms." [Encyclopedia Brittanica]
There is within the Angiosperms a
general trend from primitive beetle and fly pollinated flowers towards more
advanced pollination by butterflies, moths, birds and bees.
Flowers pollinated by bees show the
greatest degree of nectar/scent/coloration/diversity/pollen production, as well
as diverse specialisation of flower structure.
Primitive flowers tend to be trumpet
or saucer shaped [Ranunculus, Hibiscus, Magnolia, Malva, Lavatera (belonging to
malvaceae), Cucurbita and Papaver], while more advanced flowers may be tubular
[Symph./Dig./Lamium/Erica/Datura/Nicotiana], or zygomorphic. Incl. Orchis,
Antirrhiunum, Pisum, Lobelia, Viola, Gentiana, Wisteria, Mimulus, Lonicera and
Begonia.
Two directions of adaptation exist
from polypetaly [many petals] to oligopetaly [fewer petals] and from separate
petals to sympetaly [fused petals]
However, simple flowers, as in
Commelinidae [Grasses/Sedges/Rushes and Euphorbiales] may not be primitive, but
derived from more complex forms in the Liliales. This, their simplicity is
secondary
and a form of structural degeneracy
rather than a primitive feature.
Another important trend is away from
single flowers [Papaver/Ranunculus/Nel.] towards multiple flowers in racemes,
spikes, whorls, and heads [Lamium/Scrophularia/Genitiiana/Borago/Laburnum/Plantago/Achillea/Salix].
This trend reaches its height of perfection in the Dipsacales, the Umbelliferae
[Apiales] and above all in the Asterales.
The Asteraceae compound flowers are
really a spike or whorl of flowers that has failed to expand vertically and all
the flowers are packed side by side instead on a flat head [capitulum]. You can
still
trace the spiral patterns in
Helianthus heads, for example, where the whorl-like pattern of the raceme would
have unfolded if it had elongated vertically.
The inflorescence of daisies
therefore give the appearance of a raceme that has been compressed downwards
forcing all the individual flowers to become pressed tightly into a side by
side arangement
on a flat head [Bellis/Achillea].
The dome shape of the Dipsacales flowers is similar, like an early version of
this arrangement, but in the umbels of the Umbelliferae each individual flower
still retains its own separate stalk and bracts.
In recent years the old classification
has been drastically revised, mosty through the work of taxonomists Arthur
Cronquist in the USA and Armen Takhtajan in Russia. The Angiosperms are now
divided into two groups [classes] like before, but now called Magnoliopsida
[Magnolia like] and the Liliopsida [Lily like] - being broadly the same as the
older Dicots and Monocots respectively.
The Magnoliopsida are subdivided
into 7 subclasses each divided into orders and the orders divided into
families. The Liliopsida are divided into only 4 sub-classes and again into
orders and families.
Liliopsida
Subclass Alismidae - 3 orders
including frogbit, water plantain, flowering rush, eel grass, pondweed
Subclass Liliidae - 5 orders
including Orchids, Ginger, Arrowroot, Iris, Lilies, Onion, daffodil
Subclass Commelinidae - 7 orders
including grasses, sedges, rushes, pineapple
Subclass Arecidae [Spadiciflorae] -
5 orders including palms, duckweeds and Arum lilies
Magnoliopsida
Subclass Magnoliidae - 6 orders -
magnolias and relations
Subclass Ranunculidae - 5 orders -
buttercups and relations
Subclass Hamamelididae - 15 orders -
witch-hazel and relatives
Subclass Caryophyllidae - 5 orders -
elder and relations
Subclass Dillenidae 17 orders -
Paeonies, violets and myriad relations/ Hibbertia
Subclass Asteridae 8 orders -
daisies and myriad relations
Subclass Rosidae - 19 orders - Roses
and myriad relations
The links between the various
groupings listed above needs to be brought out in more detail in order to
appreciate the shape and contents of the group as a whole. The most primitive
group are
the Magnoliales, from which all the
others have evolved. They consist mostly of small trees and woody shrubs with
large upright flowers composed of many large pale petals surrounding the
many ovules and anthers forming a
spike in the centre. They are mostly beetle and fly pollinated.
In general terms we can see from the
diagrams that the entire group is derived from a primitive Angiosperm that gave
rise to the Magnoliales and the Nymphaeales.
The Liliopsida is divided into 4 subgroups.
The first and most primitive includes all aquatic plants, the Alismales,
Hydrocharitales [derived from the Alismales] and the Najadales.
Both Alismales and Najadales are derived
from the Nymphaeales and those in turn from a primitive Angiosperm or common
ancestor of the Magnoliales.
Apart from a couple of minor
families, the Magnoliales then gave rise to 4 main branches:
1. the woody Trochodendrales to
Hamamelidales branch, which forms the Hamamelidae and are almost all trees like
Walnut, beech, Birch, Elm, Oaks, Alder, etc;
2. the largely herbaceous
Ranunculales with various offshoots including the Lotuses, Poppies and
Caryophyllales - the latter including the Cactaceae;
3. the hugely adaptive and important
Dilleniales, a very large herbaceous group including 3 major divisions- the
Violales, Theales and Malvales, with numerous other important subgroups and
families;
4. the advanced Saxifragales and
their two main offshoots, the Rosales/Fabales and the Asteridae. Most of these
are also herbaceous, though with some important woody exceptions.
These are derived from aquatic
plants [the Nymphaeales and Alismatales], and many still retain their fleshy,
hydrophilic, semi-amphibious preferences [reeds, rushes, irises and sedges].
These plants often have fleshy bulbs
and corms from which they can regenerate vegetatively. The more simple and
primitive are colourful, showy and insect pollinated [Irises/Lilies] while many
of the most advanced and specialised
are wind pollinated, such as the grasses/sedges/rushes. Many of the grasses are
also xeromorphs [dryness loving] which have been liberated from the
hydrophilic habits of their ancestors.
Orchids are the most extreme example of advanced and specialised liliopsids
showing extreme insect adaptation with zygomorphic scented flowers with
remarkable specilaisation of shape
and coloration. n of shape and coloration.
Magnoliidae
These are mostly woody trees and
shrubs and all are regarded as the most primitive of the Angiosperms in
general.
Trochodendrales to Hamameliidae
These are mostly woody shrubs and
trees, wind pollinated. Most of the important tree species are in this group,
incl. Elms, Oaks, Ash, Beeches, Birches, Walnuts and Alder.
Rafflesiales and Aristolochiales
These are mostly large, tropical
herbs, specialised and obscure plants that probably represent evolutionary
cul-de-sacs. Strangely shaped and coloured.
These are mostly herbaceous plants,
often with actinomorphic, simple flowers, not especially fragrant or scented.
Predominantly with white or yellow flowers.
Examples include Berberis,
Ranunculus, Aconitum, Anemone, Pulsatilla.
Mostly actinomorphic and showy very
colourful flowers with numerous petals and numerous anthers; abundance of
pollen; they give a general impression of proliferation and abundance.
Dilleniidae
Woody or herbaceous; often fleshy
plants with large showy flowers and soft velvety leaves. Large trumpet-shaped
flowers are common throughout the group [Theales, Malvales, Passiflorales, Cucurbitales, Primulales] or in tufts [Salicales,
Tamaricales]
or more rarely small and inconspicuous [Violales, Ericales, Euphorbiales, Cruciferae and Begoniales].
As a group, these plants generally
have very colourful flowers, with an abundance of pollen and anthers but not
often very highly scented, fragranced or nectared flowers
Rosidae
Advanced and recent geologically.
Woody or herbaceous; numerous types; nectar and scented, colourful, showy, 5
patterned flowers; mostly actinomorphic but some zygomorphic [Leguminosae, Linaceae,
Hippocastanaceae,
Balsaminaceae].
Asteridae
Mostly herbaceous; derived from Saxifrages,
numerous types; very advanced, recent and most evolved plants on earth; great
tendency to flowers in spikes, compounds, umbels and heads of densely crowded
flowers. Examples include Dipsacales, Gentianales, Boraginaceae, Scrophulariales, Lamiales, Asterales.
These plants also often contain a
lot of essential
oils, aromatic compounds and thus form medicinally important groups. Examples
incl. members of the Asterales, Lamiales, Dipsacales, Scrophulariales,
Campanulales.
Actinomorphic – radially symmetrical
flower – e.g. daisy
Zygomorphic – vertically or
bilaterally symmetrical flower – e.g. snapdragon
Vorwort/Suchen Zeichen/Abkürzungen Impressum