Inventaire et distribution des rhéophytes au Cameroun

Abstract

Rheophytes are abundant macrophytes in tropical river systems where they are adapted to extreme environments of rushing water (e.g., river rapids, waterfalls and flash floods). They are useful indicators of river health and are threatened by climate change and human activities. Rheophytes are not well known in Cameroon. The main objective of this work was to contribute to the floristic and ecological known of Rheophytes in Cameroon. Missions were carried out in thirty rivers in Cameroon during the dry and wet seasons between 2010 and 2014. Notes were taken on the habitat conditions, and characteristic rheophytic features of the species encountered, particularly the leaf shape, stem characteristics, rooting system. Also additional data concerning habitat conditions and characteristic rheophytic features was generated from studies in herbarium and literature. Description of morphological and structural characters follow classical principles, while, phytogeographical classification follows modern principles of phytogeography. The conservation status of species was assessed and discussed following the IUCN Red List categories and criteria. An upgraded check-list of Rheophytes in Cameroon is produced containing 125 species distributed in 30 Families and 65 Genera. Among these species are 67 obligate rheophytes from 16 Families and 29 Genera. The morphology of the Rheophyte censused is generally marked by the gregarious aspect, a large root system, a flexible and tough stem, a foliar shape oblong-lanceolate, lanceolate, linear or rubannate; an acuminate or acute leaf apex, a glabrous foliar texture and entire margin. The reproductive organs for Rheophyte in Cameroon are not uniform but are close with the reproductive period which even though occur throughout the year is maximum during the dry seasons when the water levels are receded. Majority of the Rheophytes found in Cameroon are generally present on sand and rocks, in low current rivers and in the evergreen rain forest of equatorial climate. About 79 % of Rheophyte present in Cameroon are threatened. The main threats are agriculture, plantation development, illegal forest logging, alluvial mining, polluted water and dam construction. About 27 % of the rheophytes censused are endemic to Cameroon and are all threatened, with about 90% found in south west Cameroon. About 67 % of rheophyte species found in Cameroon are confined to the Guineo Congolian Region. About 75 % of rheophyte censused prefer the regime of equatorial climate of 4 seasons, with abundance in equatorial climate of 2 saisons and 25 % prefer the tropical climate of 2 seasons. About 75 % of the rheophyte found in Cameroon are herbaceous and 25% are trees. The Podostemaceae and Rubiaceae possess the highest number of rheophyte in Cameroon with the highest number of herbaceous species and trees respectively. The biodiversity of Cameroon in rheophyte species is among the most important in Africa. The Sanaga basin is the hydrographic basin where the highest numbers of rheophyte species were found. The abundance and the species richness of rheophyte species decrease with altitude, longitud and latitud.