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

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 the Alismales and the 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.

Liliopsida

These are derived from aquatic plants [the Nymphaeales and Alismatales], and many still retain their fleshy, hydrophilic, semi-amphibious preferences [e.g. 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, including Elms, Oaks, Ash, Beeces, 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.

Ranunculales

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.

Caryophyllidae

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 [e.g. Theales, Malvales, Passiflorales, Cucurbitales, Primulales] or in tufts [e.g. Salicales, Tamaricales] or more rarely small and inconspicuous, eg. 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 [e.g. 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 include 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