Staurastrum pantanale K.R.S. Santos, Malone, Sant’Anna & C.E.M. Bicudo

Staurastrum pantanale K.R.S. Santos, Malone, Sant’Anna & C.E.M. Bicudo , sp. nov. ( Fig. 2 A – J View FIGURE 2 ; Fig. 3 A – C View FIGURE 3 )

Type: — BRAZIL. Mato Grosso do Sul: Corumbá, Pantanal da Nhecolândia, Lagoa Salitrada Campo Dora , 18º 58’ 02” S, 56º 38’ 59” W, 8 May 2005, K.R.S. Santos s.n. holotype SP390914 ! GoogleMaps ).

A Staurastro crenulato viso vertice 3-angulari, aspectu frontali processibus distincte convergentibus, marginibus profunde crenatis, processibus in 4 spinas breves desinentibus (ad 2 µm longas) differt. Dimensiones: Cellulae 22.4–28.0 µm longae, 10.8–12.6 µm latae processibus exclusis, 27.5–42.6 µm latae processibus inclusis, isthmus 6.5–8.9 µm latus, processus 8–17 µm longi. Zygospora globosa, 2–3(–4)-processibus furcatis, 45–49 µm diam. processibus inclusis, 22–30 µm processibus exclusis, processus 6.4–12.8 µm longi.

Cells 3 - radiate, 22.4–28.0 µ m long, 10.8–12.6 µ m wide without processes, 27.5–42.6 µm broad with processes, isthmus 6.5–8.9 µm wide, processes 8–17 µm long; median constriction deep, sinus acutangular; semicell irregularly rectangular without processes, basal margin slightly convex, apical margin broadly convex; lateral angles are produced to form rather stout, distinctly convergent processes, tipped with 4 short teeth (up to 2 µ m long); all margins deeply crenate; cell wall provided with minute acute granules in concentric series on the processes; vertical view cell 3-angular, margins regularly concave, sometimes almost straight at the mid portion, with a pair of emarginate verrucae within the margin; chloroplasts axial, 1 per semicell, 2-furcate in each angle in vertical view; zygospore globose, with several 2–3(–4)-furcate processes, wall slightly rugose, 45–49 µm diam. with processes, 22–30 µm without processes, processes 6.4–12.8 µm long.

Habitat:— Metaphyton in a shallow pond with filamentous green algae and macrophytes (pH = 5).

Etymology:— The epithet pantanale is based on the name of the geographic region, the Pantanal, where it was found.

Observations:— Staurastrum pantanale differs morphologically from previously described taxa in its distinctly convergent processes (in frontal cell view) with a deeply crenate outline ( Fig. 2 A–C View FIGURE 2 ; Fig. 3 A–B View FIGURE 3 ) and cell dimensions ( Table 2 View TABLE 2 ).

Staurastrum pantanale is characterized by a subcylindric base of the semicell body ( Fig. 3 A View FIGURE 3 ). In this feature it resembles representatives of the Staurastrum manfeldtii Delponte (1877: 160) species group ( Coesel 1992), in particular S. manfeldtii var. parvum Messikommer (1942: 173) . However, it differs from S. pantanale by the short and slightly convergent apical processes (in frontal view), by the straight margins between the processes (in vertical view), which are tipped with 3 spines, and by the undulate-serrulate cell wall ( West et al. 1923).

Staurastrum crenulatum ( Nägeli 1849: 129) Delponte (1877: 68) differs from S. pantanale by the short and straight or slightly divergent processes, by the vertical view 3–5-angular with a deeply concave margin among the processes tipped with 2–3 spines, and the cell wall is crenate-denticulate ( Table 2 View TABLE 2 ). Staurastrum pantanale presents distinctly convergent processes tipped with 4 spines and a straight or slightly concave margin between the processes (in vertical view) ( Fig. 3 A–B View FIGURE 3 ; Table 2 View TABLE 2 ).

All studied populations (n = 100) showed either immature ( Fig. 2 I View FIGURE 2 ) or mature ( Fig. 2 J View FIGURE 2 ; Fig. 3 C View FIGURE 3 ) zygospores, allowing the description of their morphological details under SEM, such as their 2–4-furcate processes at the apex ( Fig. 2 H View FIGURE 2 ) and the slightly rugose wall ( Fig. 2 I–J View FIGURE 2 ). Both S. manfeldtii var. parvum and S. crenulatum never had their zygospores described, making the comparison with S. pantanale impractical. It is worth emphasizing that the occurrence of zygospores is seldom documented in the desmid literature, and that their description is extremely important since it may help to differentiate infrageneric taxa within desmids ( Ricci 1990). According to Cushman (1905), a detailed study of the zygospore of a considerable number of species is needed to evaluate its use for separation at the species and infraspecific levels in desmids. Although Cushman’s statement dates from 1905, the question still remains open without a solution.

Staurastrum manfeldtii var. parvum and S. crenulatum are quite common in temperate regions and only the latter is considered to have a worldwide distribution ( Prescott et al. 1982). Nevertheless, S. crenulatum was never referred to Brazil, and even for South America there is only one citation for Argentina ( Tell 1980). Staurastrum pantanale was collected from a very typical tropical environment. Despite having collected material in 40 sample units from different ponds in the Nhecolândia Pantanal, including “salinas”, “salitradas” and “baías”, the species was exclusively from “salitrada” ponds. Staurastrum pantanale was extremely abundant in the latter systems towards the end of the rainy season (May 2005), living in acidic (pH = 5) and relatively low electrical conductivity (648 µS.cm -1) conditions that are favorable for the growth of many desmid species ( Brook 1981, Coesel 1996). The present species occurred in the metaphyton among dense populations of filamentous green algae, mainly Oedogonium subdissimile Jao (1979: 325) , O. punctatum Wittrock (1878: 142) , Oedogonium sp. , Chara spp. and Spirogyra spp.