Özet:

Althenia F.Petit is a submerged aquatic plant genus, which is represented by two species in the world. Althenia species are found mainly in brackish water lagoons and in salt lakes. The genus has only one species in Turkey, Althenia orientalis (Tzvelev) García-Mur. & Talavera which was collected from Turkey in 1959 and published in 1975. Since then, it could not be collected again and was assessed as extinct in Turkey. We performed field studies to collect the species in May 2017 and June 2017. We managed to find the species in its original locality. We measured chemical and physical properties of the water bodies it is growing. Additionally, we provide the stem anatomy of the species based on Turkish material for the first time. The single locality of the species in Turkey is a hypersaline lagoon lake (Lake Tuzla, Adana). Only dense Ruppia maritima L. population accompanies the species. Althenia orientalis grows in slightly alkaline and warm waters. The population size is small, covering approximately 500 m2 area. The plants future presence is threatened by severe human pressure (i.e. pollution due to construction waste deposits and dense agricultural activities).

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