Dictyota falklandica F.C.Küpper, A.F.Peters, A.O.Asensi & O.DeClerck, 2019

Küpper, Frithjof C., Peters, Akira F., Kytinou, Eleni, Asensi, Aldo O., Vieira, Christophe, Macaya, Erasmo C. & De Clerck, Olivier, 2019, Dictyota falklandica sp. nov. (Dictyotales, Phaeophyceae) from the Falkland Islands and southernmost South America, Phycologia 58 (6), pp. 640-647 : 644

Dictyota falklandica F.C.Küpper, A.F.Peters, A.O.Asensi & O.DeClerck sp. nov.

Figs. 2–5 , 7–14

DIAGNOSIS: Species characterised by a regular to irregular dichotomously branching habit of erect blades up to 65 mm long and 5 mm wide, each branch growing by division of a meristematic apical cell. Margins of the whole thallus dotted with dormant apical cells. In situ colour medium to pale brown, retaining the same colour when dry.

HOLOTYPE: Herbarium specimen from San Carlos (F39) was deposited in the Natural History Museum ( BM), London, UK as No. BM013828094 , accompanied by vials with CTAB samples (Vial F17-186 BM013792001 ; Vial F18-203 BM013792002 ; Vial F17-182 BM013792003 ).

ISOTYPE: An isotype from North Arm was deposited in the Muséum National d’ Histoire Naturelle – Paris, as no. PC 0776066 . Material from the 3 live cultures fixed in CTAB buffer was deposited in the Muséum National d’ Histoire Naturelle – Paris, accompanying the isotype specimen, as no. PC 0776066 .

TYPE LOCALITY: Blue Beach , San Carlos, East Falkland, Falkland Islands, 51º 34.2676 ʹ S, 59º 2.1236 ʹ W. The type locality of this species at San Carlos is historically significant as the landing site of the forces who liberated the Falkland Islands in 1982.

ETYMOLOGY: The organism is named after the Falkland Islands, where the type material was collected.

REPRESENTATIVE SEQUENCES: MK516759 – MK516759 (cox 1) and MK516799 - MK516800 (psb A), and MK516815 (rbcL).

ISOTYPE CULTURE: A unialgal culture isolated on 31 January 2017 from the type material collected at San Carlos was deposited in the Culture Collection of Algae and Protozoa (no. CCAP 1335 /1).

Vegetative and reproductive morphology

Dictyota falklandica grew upright, but lacked a conspicuous base. The species was attached by patches of rhizoids, present near basal parts of thalli ( Fig. 8 ). Apices were obtuse, with protruding lens-shaped apical cells. Irregular branching in the apical parts of thalli might be related to regained meristematic activity of additional apical cells which dot the margins of the apical parts of the thallus ( Figs. 7, 9 ). Dichotomies were evenly spaced every 13–15 mm. The branching angle was approximately 45–50°. Surface and margins were smooth, and lacked teeth or proliferations ( Fig. 11 ).

The thallus was composed of a single-layered cortex and medulla ( Figs. 13 –15). Tangential divisions of cortical and medulla cells, resulting in a multi-layered cortex or medulla, were not observed, not even in the most basal regions. Cells contained multiple discoid plastids devoid of pyrenoids. Cortical cells were rectangular to nearly isodiametric in surface view ( Fig. 9 ), (22–) 30 (–38) μm long, (12–) 17 (–22) μm wide and 10–12 μm high ( Figs. 12, 14 ). Medullary cells were (77–) 101 (–129) μm long, (46–) 57 (–77) μm wide ( Fig. 9 ) and 95–120 μm high ( Fig. 14 ).

Male and female gametophytes were not observed. Immature sporangia occurred in irregular groups or longitudinal lines on the thallus surface ( Fig. 12 ). Sporangia were not surrounded by an involucrum and were borne on a single stalk cell. Thalli had tufts of hairs randomly scattered on both surfaces ( Fig. 13 ).

Temperature tolerance

Two months after the start of the experiment, cultures of the three isolates exposed to 25 °C for 11 days showed clear signs of stress – two were dead, and one culture was mostly bleached with only small tissue parts remaining pigmented. In contrast, the cultures at 20 or 15 °C for the same duration had healthy (brown – dark brown) pigmentation and growth.

Figures

Figs 2–5. Dictyota falklandica sp. nov. in its natural habitat at North Arm on 26 January 2017, with epiphytes on its thallus and surrounding vegetation. Scale bar = 5 mm.

Figs 7–14. Herbarium specimens and micrographs of Dictyota falklandica sp. nov. Fig. 7. Isotype (PC accession no. 0776066). Scale bar = 5 cm. Fig. 8. Surface view, with walls of larger medullar cells indicated by black lines. Scale bar = 50 µm. Fig. 9. Holotype specimen (BM accession no. BM013828094). Scale bar = 5 cm. Fig. 10. Apical region of branching thallus, with actively growing apical cells (asterisks) as well as marginal dormant apical cells (arrowheads). Scale bar = 1 mm. Fig. 11. Spores on thallus surface in irregular longitudinal groups. Scale bar = 50 µm. Fig. 12. Cross section of thallus with two hair tufts. Scale bar = 100 µm. Fig. 13. Cross section of central blade area. Scale bar = 100 µm. Fig. 14. Cross section of blade margin. Scale bar = 100 µm.