A field guide to Kenyan mangroves

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Avicennia marina (Forsk.) Vierh. 1907

Family: Avicenniaceae

Distribution
This mangrove tree (Avicennia marina) probably displays one of the broadest distributions over the Indian Ocean to the Western Pacific when compared to other mangrove trees of the region. Bruguiera gymnorrhiza comes close to the distribution of Avicennia marina, but Avicennia marina is more tollerant to extreme conditions in higher latitudes. In Kenya, Avicennia marina typically displays a double zonation pattern, occuring on the coastal edge of the mangroves as tall trees (up to about 15 m), as well as on the terrestrial edge, often exhibiting various degrees of dwarf-growth depending on the salinity and on the drainage of the site.

Leaves
Leaves of A. marina exhibit a lot of variation depending on the salinity of the environment. In areas with low salinities, leaves are lanceolate, with a pointed apex and are on average 15 cm long. In an extremely saline environment, leaves are more elliptical with a rounded apex ; they are more leathery and are very small (2cm length in extreme conditions). The underside of the leaves have a typical greyish-whitish color, due to the presence of small hairs. On the upperside of the leaves, salt cristals, excreted by the leaves can be observed. Gillikin et al. (2004) determined that these are the choice leaves for Neosarmatium meinerti.

Root system
The above ground root system of Avicennia marina is characterized by upright pencillike pneumatophores which originate from an underground cable root. The length of these pneumatophores seem to be dependend on inundation time. More uncommon on Avicennia marina are short aerial roots originating directly on the stem, usually very close to the ground, but often just hanging from the stem without anchoring in the ground.

Flowers
Very small, typically 0.5 cm, orange in color

 

Fruit
A. marina has developped a certain degree of viviparity, refered to as criptoviviparity (the embryo grows out of the seed coat, but does not emerge from the fruit). The seeds of A. marina have a velvet capsule.

 

References:

Gillikin, D.P., B. De Wachter and J.F. Tack, 2004. Physiological responses of two ecologically important Kenyan mangrove crabs exposed to altered salinity regimes. Journal of Experimental Marine Biology and Ecology 301(1):93-109. (http://authors.elsevier.com/sd/article/S002209810300474X) (REPRINT)

Tomlinson, P.B., 1986. The Botany of Mangroves. Cambridge University Press. Cambride Tropical Biology Series. 413 pp.

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all text copyrightę 2003 David Gillikin and Anouk Verheyden
Created 13 April 2002

updated: 01-Mar-2003
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