Some interesting desmids (Desmidiaceae, Zygnematophyceae): first records, taxonomic notes, and distribution for the Amazon Brazilian flora

. We report nine interesting desmid taxa, which five were recorded for the first time for the Amazon Brazilian flora, including first records of two infraspecific taxa from Brazil. The material was collected from an Amazon flooded area in the state of Amapá, Brazil. A description, geographical distribution in Brazil, water conditions, and frequency of occurrence are provided for each taxon. Our study expands the knowledge of desmids by providing taxonomic notes and information on geographic distribution.


Introduction
The family Desmidiaceae Ralfs is the largest, most diverse, and polyphyletic algal group belonging to the class Zygnematophyceae that occurs in freshwater habitats (Brook 1981;Gontcharov and Melkonian 2010). According to Guiry and Guiry (2022), the family nowadays comprises over 2,700 species, most of which were mostly proposed in 19 th and 20 th centuries exclusively on the basis on morphological grounds (Gontcharov 2008;Guiry and Guiry 2022).
Most studies on the desmid flora have focused mainly on the states of Amazonas and Pará and were NOTES ON GEOGRAPHIC DISTRIBUTION conducted in several aquatic ecosystems, including floodplains, shallow lakes, wetlands, and rivers. Especially for flood plains, the three types of water-clear, white, and black-are important in the dynamics and structure of the algal community (Junk et al. 1989;Souza and Melo 2010). In clear-and white-water floodplains there are more species reported in the literature as the result of the greater number of studies in these environments (Melo and Souza 2009).
Studies of the taxonomy and description of microalgae are still incipient for the state of Amapá. Even so, desmids constitute the best known and most recorded group of algae in the state's aquatic ecosystems. Förster (1963) was the pioneer in recording the occurrence of desmids in the aquatic ecosystems of Amapá. He reported five taxa belonging to the genera Closterium Nitzsch ex Ralfs, Desmidium C.Agardh ex Ralfs, and Euastrum Ehrenberg ex Ralfs.
Only about half a century later, the second taxonomic study was published by Souza and Melo (2011), who identified and illustrated 35 species and three varieties of Desmidiaceae-in the genera Staurastrum Meyen ex Ralfs, Staurodesmus Teiling, and Xanthidium Ehrenberg ex Ralfs-from Lake Novo, in coastal Amapá. Most recently, Araújo et al. (2020) published the third paper, this time on the pseudofilamentous desmids and including the descriptions and illustrations of 21 taxa.
To increase knowledge on the biodiversity and distribution of desmids from northern Brazil, we report on nine interesting taxa. Five taxa are recorded for the first time from the Amazon Brazilian flora. Two species are recorded from Brazil for the first time.

Methods
The state of Amapá is located in the eastern portion of the Brazilian Amazon. According to the Köppen climate classification, the dominant climate is Am (Tropical monsoon climate) (Alvares et al. 2013). The hydrological cycle is well defined, and there is seasonality and local rainfall; thus, there is a less-rainy period from July to December and a rainy or flood period from January to June (Araújo et al. 2020).
Our study was conducted at the permanently flooded station in Lake Curralinho (00°07′54″N, 051°06′50″W), that is within the Curiaú river basin and the Curiaú Environmental Protection Area, in the city of Macapá, Amapá, Brazil. We collected samples monthly between June 2007 and July 2008 (except in October 2007), using a 20 μm mesh plankton net. Samples were immediately preserved in Transeau solution (Bicudo and Menezes 2017).
Temporary slides were prepared for observation under a light microscope (Zeiss, Axio Lab A1). Photomicrographs were taken at 400× magnification with an image capture system coupled to the light microscope. Classic and contemporary literature, including taxonomic revisions, monographs, and floristic works were used for specific and infraspecific identification of the material. All samples are deposited at the Herbário Científico do Estado "Maria Eneyda P. Kauffmann Fidalgo" (SP), Municipality São Paulo, state of São Paulo, Brazil.
Temperature (°C) and conductivity (μS · cm −1 ) were measured with a portable probe (Lutron MO-CD-4303) in the field. In the laboratory, dissolved oxygen (mg · L −1 ) was measured with an Instrutherm MO-880 digital probe, and pH with a Qualxtron 8010 pH meter.
The frequency of occurrence of each species for sample unit was calculated in terms of percentage according to the formula F = n · 100 / N, where n is the number of samples in which the species was recorded, and N is the total number of samples analyzed (N = 11). Frequency categories were determined according to Matteucci and Table 1. Abiotic variables and seasonal occurrence of desmid taxa at Curralinho lake from June 2007 to July 2008 . Abbreviations: EC = electric conductivity (μS · cm −1 ); T = temperature (°C); DO = dissolved oxygen (mg · L −1 ); FA = absolute frequency; and the number of each taxon recorded during the period of study; FR = relative frequency (%); U = uncommon; R = rare; BP = both rainy and less-rainy periods; RP = rainy period, LR = less-rainy period. *Mean (min.-max.) values.  (1982): very frequent (F > 70% occurrence), frequent (F > 40 < 70%), uncommon (F > 10 < 40%), and rare (F < 10%). The absolute frequency corresponds to the number of samples in which one species occurred (Table 1).
Remarks. This species was described by Förster (1964) based on material collected in "Rio das Femmeas, Porta Azul", now considered as state of Tocantins. Our material has larger cell dimensions than reported by Förster (1964) and by Estrela et al. (2011). Our measurements were, however, smaller than those reported by Sophia (1999). Identification. Cells 1.1-1.3× longer than broad. Semicells ellipsoid to oblong. Apex widely round, with a series of short slightly curved spines. Lateral margins concave, with 8 longer spines and several small ones.   Identification. Cells 1.1× longer than broad. Semicells kidney-shaped. Basal angles and most of the lateral margins form a continuous broad curve with the upper margins slightly retuse below the apex in the mid-region. Apical margins with 2 short spines in the mid-region and 2 short ones on the extremities of the apex.  (Förster 1964;Bicudo et al. 2014). We observed specimens with large granules at the extremities of the semicells and comparatively smaller granules at the mid-region of the apex of semicells in our material. Figure 6 Basionym. Docidium sceptrum Roy (1883) Remarks. The species is commonly cited as Pleurotae nium tridentulum (Wolle) W. West var. tridentulum. However, P. sceptrum was described by Roy (1883: 37) as Docidium sceptrum, whereas Docidium tridentulum Wolle (the basionym of P. tridentulum) was described by Wolle (1884: 52). Therefore, following the International Code of Nomenclature for Algae, Fungi, and Plants (Turland et al. 2018), the first published valid name has precedence. Thus, P. sceptrum is the earliest valid published name for this species and P. tridentu lum described in West (1892: 120) must be considered a taxonomic synonym. It is important to mention that P. sceptrum was only cited by Nägeli (1849: 104), with no description or illustration included. Furthermore, P. tridentulum was erroneously described by Wolle (1884) as having three apical teeth, although there are always four teeth. Remarks. According to Prescott et al. (1982), S. fur catum var. scaevum differs from the typical variety by having a supernumerary asymmetrical 2-spinate process on the left side of each angle in vertical view. In some specimens, such processes may have degenerated into a long, simple spine (Scott and Grönblad 1957). Our measurements and illustrations are similar to those by Scott and Grönblad (1957) and Prescott et al. (1982) from material collected in the United States. Figure 10 Material examined. Remarks. The cell dimensions of our material are in accordance with those presented by Paula et al. (2014) for specimens from Mato Grosso. According to Šťastný (2010), this is a rather rare species in oligotrophic, strongly acidic environments with pH values of 3.7-4.1 and electrical conductivity of 37-93 μS·cm −1 . However, the pH was acidic (4.9), and the electrical conductivity was very low (10.5 μS·cm −1 ) in our study. Figure 11 Basionym Remarks. This variety was proposed by Scott and Grönblad (1957) from material collected in the United States. According to these authors, S. quadrispinatum var. spicatum is identical to individuals belonging to Staurastrum spicatum West & G.S.West, and it was also not possible to easily differentiate it from the various morphological expressions they identified as Staura strum quadrispinatum Turner. Thus, according to Scott and Grönblad (1957), it was more correct to propose a new combination and transfer S. spicatum to S. quad rispinatum as a variety. Specimens of the latter variety have rectangular semicells with simple basal angles, strong spines, and apical angles with two spines. Measurements of our Amapá material are similar to those recorded by Scott and Grönblad (1957) and Prescott et al. (1982) of North American specimens. Figure 12 Basionym. Staurastrum longissimum Borge (1918) Geographical distribution in Brazil. Federal District (Leite 1990), São Paulo (Borge 1918Godinho 2005), Tocantins (Förster 1964, as Goiás state).

Remarks.
Staurastrum longissimum was originally described by Borge (1918: 47) from material collected in São Paulo state, Brazil. Later, this species was transferred by Teiling (1967) to Staurodesmus wandae as a variety of that species. This variety differs from the typical species in having cells approximately 3× longer than wide, which makes it unique and easily identifiable. Förster (1964: pl. 33, figs. 11-13, pl. 49, fig. 10 Godinho (2005) from material from São Paulo state. The predominantly acidic (pH < 5.5) and low conductivity of the water in our study area is favorable for the development of desmids. In addition, high temperatures and low dissolved oxygen (<5.5 mg·L −1 ) were dominant (Table 1). Acidity and low conductivity of water are very common in the aquatic ecosystems of the Amazon region (Melo and Souza 2009;Souza and Melo 2010), especially during the rainy season.
In terms of their frequency of occurrence, we found all taxa to be uncommon or rare, probably due to their intrinsic characteristics and ecological preferences at the time of year of the study. Seven taxa are considered uncommon or less frequent. Staurodesmus wandae var. longissimus (45%) was recorded in five of the 11 months of our study, followed by Cosmarium horridum in four months (36% of frequency). In contrast, Cosmarium or natum var. sublagoense and Staurastrum quadrispina tum var. quadrispinatum were rare (9%), present only during the rainy and the less-rainy periods, respectively (Table 1).

Discussion
We report nine taxa in four genera of Desmidiaceae. We identified two taxa to the species level and seven others to an infraspecific category. Of the infraspecific taxa, two are typical and five are non-typical varieties of their respective species. The most representative genera were Cosmarium and Stautasrum (three taxa each one), followed by Pleurotaenium (two taxa) and Staurodesmus (a single taxon).
Our analysis of the seasonal occurrence of desmids during our study from June 2007 to July 2008 showed that most taxa occurred during both rainy and lessrainy periods (Table 1). However, three taxa were exclusively recorded during the rainy period (C. ornatum var. sublagoense, P. coronatum var. luetzelburgii, and S. fur catum var. scaevum), and S. quadrispinatum var. quadri spinatum was only recorded for the less-rainy period.
The taxa reported here are distributed in seven Brazilian states: Amapá (present study), Bahia, Mato Grosso, Paraná, Rio de Janeiro, São Paulo, and Tocantins (previously as Goiás state), as well as the Brazilian Federal District (Fig. 13). The states of São Paulo and Tocantins showed the greatest number of taxa (four each). Cosmarium horridum is well distributed in Brazil (in five states), followed by C. furcatum, P. sceptrum var. sceptrum and Staurodesmus wandae var. longissimum in four states (Fig. 13).
The number of desmid taxa (Zygnematophyceae) currently recorded from northern Brazil is 331 distributed into 23 genera (Flora e Funga do Brasil 2022). However, this number is probably underestimate. According to the Flora do Brazil (Flora e Funga do Brasil 2022) database, the microalgae flora of Amapá comprises just 18 taxa belonging to the two genera Staura strum and Staurodesmus. Although there are still few studies and information is lacking on the microalgal flora of this state, other genera have been reported from aquatic ecosystems in Amapá, including Closteri um and Euastrum (Förster 1963), Desmidium (Förster 1963;Araújo et al. 2020), some other pseudofilamentous genera (Araújo et al. 2020), and Xanthidium (Souza and Melo 2011).
All taxa that we found are reported here for the first time from Amapá. The following five taxa are additions to the desmid flora of the Amazon region: C. horridum, P. sceptrum var. sceptrum, Staurastrum quadrispinatum var. quadrispinatum, S. quadrispinatum var. spicatum and S. furcatum var. scaevum. The last two are also reported for the first time from South America and Brazil.
Four taxa were recorded by Förster (1964) from Rio das Femmeas, Porta Azul (Cosmarium furcatum, C. or natum var. sublagoense and Staurodesmus wandae var. longissimus) and Conceição (Pleurotaenium coronatum var. luetzelburgii). In 1964, prior to the formation of Tocantins, these localities belonging northern of state of Goiás, but nowadays, since the separation of these both Brazilian states, they are within the state of Tocantins. After 58 years, we can report these four taxa for only the second time from the Amazon Brazilian flora.
Both species newly reported from Brazil by us were descripted from material collected in North America by Scott and Grönblad (1957), and there is currently no detailed information available on their distribution in the AlgaeBase database (Guiry and Guiry 2022). Some other taxa reported here are of common or may be endemic to tropical South America, such as C. furca tum and C. horridum (Coesel 1996), C. ornatum var. sublagoense (Förster 1964;Biolo and Bicudo 2018), and S. wandae var. longissimum (Borge 1918;Bicudo et al. 2018). Three taxa, P. coronatum var. luetzelburgii, P. sceptrum var. sceptrum, and S. quadrispinatum var. quadrispinatum, are widely distributed around the world (Guiry and Guiry 2022).
Finally, we emphasize the need for more taxonomic revision and investigations on desmids, as well as other microalgae groups, especially in Amapá, where knowledge is still poor compared to other Brazilian states.