Abstract
The Caatinga domain is the largest and most diverse tropical semiarid ecoregion of South America; however, little is known about the diversity of desmids it harbors, especially the genus Cosmarium (Desmidiaceae, Zygnematophyceae). Our study contributes to the knowledge of Cosmarium in the Caatinga through the report of 42 interesting taxa, including a new species (Cosmarium imperiale), 22 new records for South America, and 19 additions to the desmid flora from Brazil. The samples were gathered from periphytic material from the “Pantanal dos Marimbus” in the Chapada Diamantina region of Northeast Brazil. We provide taxonomic notes, ecological information, including habitat conditions with limnological data, and updated global distributions for all taxa of Cosmarium. A complementary quantitative study was performed during the last year of sampling (2018), which revealed that most taxa have their highest densities in the months with low precipitation and when the water's conductivity and transparency are greater. Our results also have implications for the conservation of the biota from Marimbus do Baiano and understand South America's desmids' biogeography since some rare taxa identified here were previously only known from other continents such as Europe and Africa.
Highlights
South America is characterized by having a mosaic of phytogeographical domains, with diverse types of environments from dry deserts to very wet rainforests and semiarid areas (Moro et al 2016)
To increase the knowledge on the biodiversity and distribution of desmids from the Caatinga, the present paper reports 42 interesting taxa of Cosmarium, including a new species and rare taxa reported or confirmed for the first time to the desmid flora of Brazil or South America
One hundred periphytic samples were collected during the years 2011, 2012, 2017, and 2018 in the “Pantanal dos Marimbus”, a floodplain located between the Andaraí and Lençóis municipalities, Chapada Diamantina region, Bahia State, northeastern Brazil (Fig. 1)
Summary
South America is characterized by having a mosaic of phytogeographical domains, with diverse types of environments from dry deserts to very wet rainforests and semiarid areas (Moro et al 2016). Among the most interesting semiarid regions from that continent, one of the most interesting is the Caatinga domain, which is considered the largest and most diverse tropical semiarid ecoregion from South America This is the only biome found exclusively in Brazil (Leal et al 2003; Silva & Souza 2018). Based only on taxonomic and floristic studies (Förster 1964; Ramos et al 2019; 2020), there are only 13 taxa of Cosmarium reported to that domain (12 from Bahia and only one in Piaui), including some endemic taxa such as Cosmarium decedens var. To increase the knowledge on the biodiversity and distribution of desmids from the Caatinga, the present paper reports 42 interesting taxa of Cosmarium, including a new species and rare taxa reported or confirmed for the first time to the desmid flora of Brazil or South America
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