Stigonema parallelum, Sant’Anna, Célia L., Kaštovský, Jan, Hentschke, Guilherme S. & Komárek, Jiŕí, 2013

Sant’Anna, Célia L., Kaštovský, Jan, Hentschke, Guilherme S. & Komárek, Jiŕí, 2013, Phenotypic studies on terrestrial stigonematacean Cyanobacteria from the Atlantic Rainforest, São Paulo State, Brazil, Phytotaxa 89 (1), pp. 1-23 : 19

Stigonema parallelum Sant’Anna, Kaštovský, Hentschke& Komárek, sp. nov. ( Fig. 14 , 15 )

Strata aerophytica , fusco-atrata, tenues, atteram adhaerentes, de filis curtis, erectis, parallele agglomeratis composita. Fila bipolares, praecipue uniseriata rarisime ad tri-seriata, apud basis 10–18 µm lata, ad apices rotundatis attenuata ad 8–10 µm, rarissime elongata, flexuosa cum ramis lateralis. Rami curti, ad apices rotundati. Vaginae firmae, lamellosae, luteo-fuscae. Cellulae irregulariter rotundatae, saepe brevior quam latae vel ad isodiametricae, contentu griseo-aeruginosae vel olivaceae. Heterocytae solitariae, intercalares vel laterales subsphaericae vel irregulariter ovales. Hormogonia curta, 4–12-cellularia, praecipue 7–8 µm lata, cylindrica vel ellipsoidea, cum cellulis curtis, barriliformis composita, apice de filis ramisque separantur.—Habitatio: Aerophytice in solis latericis humidis in sylvis montium " Mata Atlantica " dictis, provincia São Paulo, Brasilia.

Type:— Brazil. São Paulo: Ecological Station “Juréia-Itatins”, preserved sample collected on 19 September 2002, C.L. Sant’Anna (Holotype SP 427516!, Isotype SP 427517!) .

Thallus forming flat mats on the substrate, composed of relatively short, parallel and densely arranged filaments, perpendicular to the substrate. Filaments mostly uniseriate, only rarely with 2(3) cells aside, wider near the bases (10–18 µm), narrowed toward the ends (8–10 µm). Branches lateral, very short, narrowed towards the ends, rounded at the apex. From the layer of short, parallel oriented filaments sometimes solitary longer, flexuous filaments grow, also with short branches, up to 3 times longer than other filaments. Hormogonia 4–12-celled, mostly 7–8 µm wide, cylindrical or ellipsoid in outline, composed of short barrelshaped cells, constricted at the cross-walls. Hormogonia are formed also at the end of elongated filaments. Sheaths slightly up to intensely lamellate, yellow-brown. Cells irregularly rounded, mostly shorter than wide, rarely isodiametric. Cell content grey-blue-green, olive green, or pale blue-green.

Habitat:— On wet lateritic soil.

Etymology:— Specific name refers to the parallel organization of filaments in thalli.

Notes:— This species represents a morphologically very distinct and characteristic stigonematacean type with heteropolar filaments, attached by one end to the substrate and very characteristic life cycle. Short, mostly uniseriate filaments are round at the apical ends, attached firmly to the substrate, and arranged very densely and parallel in erected fascicles. The short hormogonia liberate individually from the sheaths in the apical part of filaments attached to the substrate, representing the main mode of reproduction (see Fig. 15 ). The only stigonematacean species with a similar morphology and life cycle is Stigonema compactum Gardner (1927: 10) , described from China, but with a distinctly different cell morphology. Since there are no other similar known stigonematacean taxa, we describe this as a new Stigonema species. The biology and morphology of this Brazilian morphotype are so specific that the separation at the generic level might be possible in the future.

Figures

FIGURE 14 A–R: Stigonema parallelum. A: Filament with a lateral heterocyte. B: Detail of filaments with lamellated sheaths. C–F: Parallel filaments forming hormogonia. G: Long filament with short branches. H–J: Details of apices. K: Germinating hormogonia. L–R: Development of filaments and releasing of hormogonia (life cycle). Scales: 10 µm in A (use for A, B), C (use for C–D), E, F (use for F–K) and L (use for L–R).

FIGURE 15 A–F: Stigonema parallelum. A: General aspect of a thallus. B–D: Parallel filaments. E: Branched filament. F: Filament forming a hormogonium. Scales: Scales: 10 µm.