Placentation#Placentation in plants

The placenta is the site has grown to the ovule with its stalk ( funiculus ) the carpel in angiosperms. The location of the placenta in the ovary or in the carpel is very important for systematic distinctions of plants.

The arrangement of the ovules at the carpel or ovary is called placentation. The ovules are always on the adaxial side of the carpel. In the original species the attachment point is not or hardly be distinguished from the rest of the carpel, the placenta is then simply a job. In most species, however, the attachment site is a raised pad or a longitudinal rib or a complex tissue structure which may fill the entire ovary with the seeds of plants.

In free carpels

In free, non carpels there are two types of placentation:

  • Laminale placentation: Sitting here the ovules on the entire inner surface of the carpel. The laminale placentation is considered to be an original feature and occurs in Butomus, Hydrocharis and Nymphaea.
  • Marginal placentation: Sitting here the ovules in rows on the edge of the carpel, near the juncture of the carpel margins. As the ovules never stand on the edge all, their position is actually submarginal, the term is marginal, however, widespread. When the representatives of the Degeneriaceae and Winteraceae there are transitional forms of laminalar to marginal placentation.
  • Basal: In species with reduced ovule number, the single ovule is often on the lower end of the fruit and leaf springs but it seems the axis, in reality the carpel. Examples are anemone or Potentilla.
  • A single ovule can rarely start at the upper end of the carpel or in the middle. For these layers, there is no common names.

In ovary

  • Even with overgrown ( coenokarpen ) carpels there are laminale placentation.
  • Central angle Permanent placentation occurs when several carpels are fused with marginal placentation. The ovules are then in the middle of the ovary. It is regarded as an original form of placentation and is widely used.
  • Parietal placentation there in the ovary, which have no septa ( partitions ), it is therefore only a large cavity are ( parakarper ovary ). The edges of the carpels with the placentas rich more or less far into this cavity. The form occurs approximately at the cucurbits.
  • Central placentation also occurs in einfächrigen ovary. Here are the placentas in a central column that rises from below into the ovary. She is, in essence at two clans, where they differ, however, arises: the center column is created regardless of the carpels from the center of the flower crown at the Primelgewächsen. When the cloves plants the septa as in the central angle constant placentation are at a young ovary still exists, but dissolve in the course of growth, so that in the mature ovary of the septa, the center column is only left.
  • Again, there are basal placentation, such as in the Polygonaceae.

Documents

  • Arthur J. Eames: Morphology of the Angiosperms. McGraw Hill, New York 1961, pp. 204-216, 234-239.
  • Peter Leins: flower and fruit. Morphology, evolution, phylogeny, function, ecology. E. Content Free Trial, Stuttgart 2000, pp. 92f. ISBN 3-510-65194-4
  • Flower
Ovary (botany)
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