Sea reed


The sea reed is a Espèce of Plante S long-lived of the family of the Poacée S, originating in the Old world, growing in the grounds sandy thanks to a very major system racinaire. She was in particular used for to fix the littoral dunes Landes of Gascogne in France.

Systematic

Scientific name: Ammophila arenaria (L.) Link (synonym: Arundo arenaria L.), family of the Poacée S, subfamily of the Pooideae , tribe of the Aveneae . Sometimes one finds it under name Psamma arenaria .

Vernacular names: sea reed, reed of sands, ammophilous of sands, gourbet, snap ring of the dunes, marine grass, élyme of sands.

Etymology: “sea reed” is a word of origin Picard E. Ammophila comes from the Greek and means " who likes the sable". Arenaria comes from Latin arena: sand.

Description

It is a long-lived plant monocotylédone, with the stiff stems being able to reach 120 cm. The sheets green-grisâtre pointed, are frayed, at the rolled up edges. The flowers are épillet S of color yellow straw joined together in long ears in the shape of spindle; the fruits are Panicule S rather dense.
Les underground stems, or Rhizome S, is very developed and can extend on a long distance. The roots are rather strong, blanchâtres.

Reproduction

The long spindle-shaped ears are made up many épillets pedicels with only one flower. The Glume S are subégales, acute, just as the Glumelle S. glumelle the lower is indented than the top. Each flower presents 3 cheesecloths and a pistil.

Pollination is Anémophile.

Flowering takes place as of May. The ears are ripe in July.

Distribution

Distribution

This species is originating in the moderate and hot areas of the Old world:

It was naturalized in many areas, in particular in Australia, New Zealand and with the the United States.

Medium of life

The sea reed is on the littoral dunes, in the zone called " white Dune " , enough far above the upper part of the zone of swinging of the tides (tolerated maximum salinity: 2%). It is a species Xérophyte.

Adaptation to the dryness

The sea reed is graminaceous remarkably adapted to the dryness.
  1. Rolling up of the sheets: as soon as the Hygrométrie decreases in lower part of a certain threshold, specialized cells of the higher face of the sheets (the cells bulliformes) lose to them Turgescence, which induces a contraction of the skin and a rolling up of the sheet. The higher face of the sheet does not communicate then any more with the external medium only by one thin slit. In the middle of this rolling up, surface folaire is folded in many furrows called " cryptes" , where the hygroscopy remains higher than that of the medium external by limitation of evaporation.
  2. Presence of épidermiques hairs: the higher face of the sheet presents many hairs limiting the air circulation. They thus help to retain the steam emitted by evapotranspiration, thus taking part in the maintenance of a higher hygroscopy within the rolling up of the sheet.
  3. Protection of the Stoma S and limitation of their number: the stomata are present only on the rolled up higher face of the sheet. They are thus protected from the external dryness, more especially as they are generally located at the bottom of the crypts, where the hygroscopy is higher.
  4. Presence of a thick Cuticule on the lower face of the sheet, which strongly limits evaporation.

Resistance to the stranding

The sea reed resists the washing away and the burial by sand by forming Rhizome S tracing, able to extend at long distances and to give rise to new air growths. When sand is fixed by the dune vegetation and that there is no more regular arrival of sand, Nématode S parasites appear in the ground of the dune and attack the rhizomes of the sea reed, which causes its deterioration then its death.

Bonds and references

  • transverse Section of a limb of Sea reed
  • Adaptation to the dryness of the sheet of the sea reed
  • Gallery Calphotos

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