Leaf polymorphism
As Blattpolymorphismus in which is Botany different embodiment of the profile of a plant designated. Leaves of a single plant specimen can differ considerably in terms of size, shape or symmetry, depending on their location or function. An outstanding example of such differences in form and function are the mostly rounded cotyledons of the dicotyledon vascular plants , which are already established in the seed and which differ considerably from the leaves that appear later in the course of the growth of the stem axis .
Leaf polymorphism "Leaf multiformity" serves as a generic term for a number of specific names with which manifestations of leaf variability are named in more detail depending on the type and conditions of occurrence: " Leaf twig shape" Leaf dimorphism , "Uneven leafless " anisophyllous , and "Diverse leafy " heterophyllous . In most taxa, the subsequent leaves are more or less designed in the same way, "uniformity" (homo-, isophylly).
A distinction is made between modifying or induced , adaptive (dependent on external influences) and habitual , primary (genetically determined) forms of heterophyllia and anisophylly. Also mimetic adjustments are possible.
An abrupt change in the organ shape or habitus of a plant species in ontogeny is called heteroblasty (or heteroblastic series ; the change in leaf shape and size along the growing shoot). This is the case when a seed germinates and the first juvenile leaves initially have a different shape than their adult successors. In homoblasty , however, no such change occurs.
In the dicotyledons there are also the forms aniso- , hetero- and syncotyly ; the uneven formation or loss of one of the two cotyledons. Also the formation of an increased number of cotyledons pleiocotyly and tricotyly ; the formation of a third cotyledon and split schizocotyly is possible.
Heteroblastia
The time sequence of different leaf sizes during the individual development of a plant is called heteroblastic series . In vascular plants, it inevitably occurs along the primary shoot axis of the seedling . However, also during the growth of a side shoot first simple scale leaves are created, which later follow those of increasingly complex shape. Borne by the rung in the course of its further development at its end a inflorescence ( inflorescence ), the normal leaves can range from near the flower bracts will be replaced; the flowers themselves usually sit under the arm of a carrier sheet ( bracts ) with shed sheet form.
Leaf dimorphism and heterophyllia
If a plant forms two completely different leaf shapes (in different regions of the plant) in the course of its development, this is known as leaf dimorphism (heterophylly). A well-known example of this is ivy : the creeping young shoots have shadowy leaves with an angular, lobed shape, while leaves with a smooth edge grow on the adult shoots (heterophyllous age). Leaf dimorphism also often occurs in aquatic plants such as water cockfoots (e.g. Ranunculus aquatilis ), in which the plant, in addition to the pinnately slit leaves that grow submerged in the water, forms lobed air leaves that lie on the water surface ( floating leaves ).
Many authors use the term heterophylly only in connection with different functions of the leaves or when their expression clearly depends on external or internal conditions, as is the case with the water crowfoot.
Milieu dependency
In water crowfoot , the development of the respective leaf shape depends, among other factors, on the temperature (thermomorphosis); the underwater leaves develop at water temperatures around 8-18 ° C, whereas the water temperature rises to 23-28 ° C (depending on the air temperature) Water lobed leaves formed with the shape of the air leaves. The administration of abscisic acid , a phytohormone, also causes the formation of air leaves. It is assumed that turgor losses , which occur when the leaves transpire in the air and lead to the release of abscisic acid, induce the formation of floating leaves.
Different function
- In aquatic plants, the different functions of the leaves can usually be recognized by their position (transpiration under water and in the air).
- The antler ferns , which grow epiphytically on trees, form, in addition to the fertile fronds, sterile mantle or niche leaves that attach to the substrate and protect the roots and rhizomes of the plant from damage and drying out.
- In some carnivorous plants, there is a division of labor between leaves for carbon fixation ( photosynthesis ) and those for catching prey. For example, the trap has above-ground green leaves and underground, chlorophyll-free catch leaves.
Anisophylly
While completely different leaf shapes occur in heterophyllous, the term anisophyllous only describes size or slight shape differences between neighboring leaves or even leaves lying on the same node. Anisophylly can already be created in the shape of the leaf buds ( habitual or primary anisophylly as in the moss ferns ) or it can be caused ( induced ) by the position of the stem axis, as in the Norway maple , where the leaves hanging down are larger due to gravity. Other examples of anisophylly are the leaves of the horse chestnut and silver fir .
literature
- Adrian D. Bell: Illustrated morphology of flowering plants. UTB series for science . Eugen Ulmer, Stuttgart 1994, ISBN 3-8252-8089-6 .
Web links
Individual evidence
- ↑ Ulrich Kück, Gabriele Wolff: Basic botanical internship. 3rd edition, Springer, 2014, ISBN 978-3-642-45448-6 , p. 93.
- ^ Hermann Remmert: Special ecology: Terrestrial systems. Springer, 1997, ISBN 978-3-540-58264-9 , p. 40.
- ^ A b Eduard Strasburger (founder), Peter Sitte (editor), Elmar W. Weiler, Joachim W. Kadereit, Andreas Bresinsky, Christian Körner (authors): Textbook of botany for universities . 35th edition, Spektrum, Heidelberg / Berlin 2002, ISBN 3-8274-1010-X , p. 439.
- ^ Eduard Strasburger (founder), Peter Sitte (editor), Elmar W. Weiler, Joachim W. Kadereit, Andreas Bresinsky, Christian Körner (authors): Textbook of botany for universities. 35th edition, Spektrum, Heidelberg / Berlin 2002, ISBN 3-8274-1010-X , p. 195.
- ↑ Bernhard Kaussmann, Ulrich Schiewer: Functional morphology and anatomy of plants. Gustav Fischer Verlag, Stuttgart 1989, ISBN 3-437-20412-2 , p. 162 f.