First records of Zygnematales (Zygnematophyceae, Streptophyta) for the state of Bahia, Brazil

This study presents the first taxonomic inventory of the order Zygnematales in the Litoral Norte Environmentally Protected Area, in the state of Bahia, Brazil. Fifty samples of planktonic and periphytic material were collected, from lotic and lentic environments, during the summer (January-March) and winter (June-August) of 2009. We identified 18 taxa distributed among five genera (Cylindrocystis, Mougeotia, Netrium, Spirogyra, and Spirotaenia). Of those 18 taxa, eight were new additions to the Brazilian desmid flora: Mougeotia calcarea; Mougeotia elegantula; Spirogyra gracilis; Cylindrocystis crassa var. elliptica; Cylindrocystis brebissonii var. minor; Cylindrocystis brebissonii var. turgida; Netrium digitus var. parvum; and Netrium oblongum var. oblongum. The geographical distributions of ten taxa were extended to include northeastern Brazil.


Introduction
Zygnematales (Zygnematophyceae, Streptophyta) are characterized by having cell walls composed of a single unit, without pores or other ornamentations.The order comprises approximately 1000 species and 20 genera distributed between two families: Zygnemataceae, comprising 13 filamentous genera whose cells are united at their poles to form filaments; and Mesotaeniaceae (known as saccoderm desmids), comprising seven genera, composed of individual unicellular algae that sometimes form amorphous colonies within an abundant mucilaginous matrix (Gerrath 1993;Parra & Bicudo 1996;Graham et al. 2009).
To our knowledge, there have been no previous studies of the order Zygnematales in the state of Bahia, Brazil.Therefore, the present study sought to undertake the first taxonomic inventory of genera of the order within the state, with the objective of increasing the knowledge of this taxon in Brazil.

Materials and methods
The Litoral Norte Environmentally Protected Area (EPA) was created by State Decree no.1.046, on March 17, 1992.The Litoral Norte EPA covers a coastal strip approximately 144 km long and 10 km wide (Fig. 1), including five municipalities (Jandaíra, Esplanada, Conde, Entre Rios, and Mata de São João), thus constituting the second-largest EPA in the state of Bahia.
Fifty periphytic and planktonic algae samples were collected, from lotic and lentic environments, in the summer (January-March) and winter (June-August) of 2009.The collections were made following standard methodologies used in taxonomic studies of continental microalgae (Bicudo & Menezes 2006).
The metric characteristics of the populations were determined using an ocular micrometer.Photomicrographs were obtained using a digital camera coupled to an optical microscope, and species identifications were based on the specialized literature.
Samples were preserved in Transeau's solution, following Bicudo & Menezes (2006), and incorporated into the liquid collection at the Herbarium of the (Bahia) State University of Feira de Santana (code, HUEFS).

Results and discussion
Analyses of the 50 samples allowed the identification of 18 taxa among five genera, of which two belonged to the family Zygnemataceae (Mougeotia and Spirogyra) and three belonged to the family Mesotaeniaceae (Cylindrocystis, Netrium, and Spirotaenia).Morphologically, Mougeotia calcarea is similar to M. parvula Hassall, although it differs by having smaller cell dimensions and dark brown zygospores (Transeau 1926(Transeau , 1951;;Zarina et al.2008).Wittr., Bih. Kgl. Svensk. Vet.-Akad. Handl. 1: 40, pl. 3, fig. 5-8. 1872. Fig. 4 and 5. Simple filaments, vegetative cells 12-25 times longer than wide, 50-150 μm long, 4-6 μm wide, lateral margins parallel, straight, smooth, septum region straight; cell walls hyaline, smooth; chloroplast axial, laminar, twisted; Mougeotia elegantula demonstrates conjugation of the scalariform type, with quadratic zygospores, cruciate with rounded angles.In terms of its morphology, M. elegantula can be compared to M. virescens (Hassall) Borge, although differing from the latter by having larger zygospores with deeply concave sides, and larger vegetative cells.Mougeotia cf.gotlandica shows scalariform type conjugation, with globose zygospores.We only tentatively identified the present material due to the absence of chloroplasts in the cells and only small numbers of specimens in the samples.
Cells fusiform, 2.5-2.6 times longer than wide, 100-110 μm long, 39-42.5 μm wide, lateral margins more or less parallel to each other, poles truncate-rounded; cell walls smooth; 2 axial chloroplasts, with prominent lateral projections, 2-3 pyrenoids in median series per chloroplast.Distribution in Brazil: Bahia (present study).The differences between the parvum variety and the typical variety of this species are its truncate-rounded poles, chloroplasts with prominent lateral projections, and relatively smaller cell dimensions.
The var. parvum could be initially confused with Closterium closterioides (Ralfs) Louis & Peeters var.intermedium (Roy & Bisset) Růžička, although the latter has lamellate chloroplasts and apical vacuole containing one or more granules of calcium sulfate.

Figure 1 .
Figure 1.Map of the state of Bahia, Brazil. A. The Litoral Norte Environmentally Protected Area (gray highlighting).
Cylindrocystis brebissonii var.minor differs from the typical variety of this species only by having smaller cell dimensions.Morphologically, the variety minor may be confused with Actinotaenium truncatum (Bréb.ex Ralfs) Teiling ex Růžička & Pouzar, but the latter differs by having more rounded apical margins and a slight median constriction.
De Bary var.ellipticaWest & G.S.  West, Trans.Linn.Soc.London: ser.2, 5: 48, pl. 5, fig.27.Cylindrocystis crassa var.elliptica differs from the typical variety of this species by having subcircular cells with widely rounded poles.In terms of its morphology, this variety can be confused with Mesotaenium chlamydosporum De Bary var.violascens (De Bary) Willi Krieg., although the latter has smooth and straight parietal laminar chloroplasts, and its cell walls are violet colored.