Ekerewekia churiensis Kaštovský, Fučíková, Štenclová & Brewer-Carías, 2016

Kaštovský, Jan, Veselá, Jana, Bohunická, Markéta, Fučíková, Karolina, Štenclová, Lenka & Brewer-Carías, Charles, 2016, New and unusual species of cyanobacteria, diatoms and green algae, with a description of a new genus Ekerewekia gen. nov. (Chlorophyta) from the table mountain Churí-tepui, Chimantá Massif (Venezuela), Phytotaxa 247 (3), pp. 153-180 : 171-173

Ekerewekia churiensis Kaštovský, Fučíková, Štenclová & Brewer-Carías , sp. nov. ( Figs 13 , 14 )

Thallus filamentous, pale green, with monopodial, multilateral branching ( Figs 13A, B, J, K ). Main filaments long (more than 1 mm), secondary branches usually shorter (up to 100 μm), ocassionally slightly longer than 100 μm. Cylindrical cells of both main and lateral branches (8)10–13 μm wide and 25–40(60) μm long, immediately after division cells almost isodiametric ( Figs 13C, D, I ). Cells mostly not constricted at cross walls ( Fig. 13D ) or only slightly constricted ( Fig. 13E ). Apical cells cylindrical, rounded at the end, not tapered, not different from other vegetative cells. Each cell nearly entirely filled with 1–2(–4) round to oval chloroplast/s with rough edges and one distinct pyrenoid in each plastid. Cell walls firm, colorless, thin (0.5 μm), in older filaments slightly thickened (1–2 μm, Figs 13C, I ). Asexual reproduction by one- or two-celled fragments, derived from ends of filament’s branches. The ends of filaments suggest a two-pieced mother cell wall similar to the genus Microspora ( Fig. 13G ), but unlike in Microspora , overlapping pieces of cell wall are not visible in the living filaments.

Type:— VENEZUELA. Bolívar State: Guyana Highland, Chimantá Massif, Churí-tepui–Charles Brewer Cave Base Camp, Bathroom Creek, above entrance into Charles Brewer Cave, 5º 14.952’ N, 62º 1.588’ W, 2200 m a.s.l., J. Kaštovský, 17 January 2012 (holotype: CBFS! A-022, Herbarium for Nonvascular Cryptogams at the Department of Botany, Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic).

Etymology:— From the Latin adjective churiensis (inhabitant of Churí-tepui), referring to the locality where the species was discovered.

Ecology and distribution:—Epilithic on the bottom of streaming waters. At the locality of origin this species is quite abundant ( Fig. 14B ). This species was found in the only stream on Churí-tepui, and formed macroscopic, monospecific mats.

Comparison with similar taxa:— No similar green algal species is known so far. The combination of the morphological traits (long, truly branching filaments, H-shaped cell walls, and chloroplast with a single pyrenoid) is unique.

Evidence of phylogenetic separation:— Ekerewekia is nested within the Prasiola clade, class Trebouxiophyceae, with good statistical support (1.00 Bayesian posterior probability and 90–99 maximum likelihood bootstrap value) for its phylogenetic placement as sister to a coccoid prasiolalean clade. The alga belongs to the family Koliellaceae and is morphologically very different from all its close relatives. The Prasiola clade contains numerous coccoid (unicellular, vegetatively non-motile) forms as well as filamentous to thalloid forms. Ekerewekia is unique in the clade with its long, frequently branched filaments that resemble somewhat the ulvophycean genus Cladophora , combined with twopiece cell walls resembling the chlorophycean genus Microspora . The flat, sometimes almost stellate chloroplasts are slightly reminiscent of Zygnematales ( Figs 13C, D , 14D ). Analyses of both SSU and rbcL demonstrated clear distinctness of the proposed new taxon from any genus that has been studied with the use of molecular data so far. The two samples obtained in this study yielded sequences that grouped strongly together in both genes ( Figs 15 , 16 ) and were subtended by a considerably long branch.

Figures

FIGURE 13. Ekerewekia churiensis, sp. nov., microphotograph. A, B, J, K. General view, branching. C, D. Chloroplast shape. E, F, G. Micropsora-like cell walls at the end of filament. H, I. Beginning of branching. Scale bars = 10 μm.

FIGURE 14. Ekerewekia churiensis, sp. nov. A. macrophotograph. B. Type locality, Bathroom Creek, dominant part of the green biomass is E. churiensis, in the background Ch. Brewer-Carías. C. Line drawing of a general pattern of the thallus, scale bar = 200 μm. D. Line drawing of branching and chloroplast shape, scale bar = 10 μm.

FIGURE 15. Maximum Likelihood phylogenetic tree based on the analysis of SSU rRNA gene sequences of various members of the Trebouxiophyceae, with Chlorophyceae as an outgroup. Numbers at branches indicate bootstrap support from maximum likelihood (1000 replicates) and Bayesian posterior probabilities (ML/BI). Supports of ≥50 % for ML and ≥0.5 for BI are shown.

FIGURE 16. Maximum Likelihood phylogenetic tree based on the analysis of rbcL gene sequences of members of the Prasiola clade, with the Neocystis clade as an outgroup. Numbers at branches indicate bootstrap support from maximum likelihood (1000 replicates) and Bayesian posterior probabilities (ML/BI). Supports of ≥50 % for ML and ≥0.5 for BI are shown.