Paralemanea catenata Vis & Sheath

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Paralemanea catenata (Kützing) Vis & Sheath Fig. 3 A – H Basionym. Lemanea catenata Kützing. Homotypic synonym. Lemanea catenata Kützing. Heterotypic synonyms. Paralemanea pleocarpa M. L. (Atkinson) Vis & Sheath; Lemanea nodosa Kützing; Lemanea pleocarpa Atkinson. Type locality. Rheingegend (i. e. Rhine river area, France or Germany) (Vis and Sheath 1992). Previous record in Italy. Listi stream (Aspromonte, southern Italy) (Mannino et al. 2003). Sampling site. Monte San Nicola and Passo Mojo. Herbarium specimen. Deposited in CAT Herbarium – sectio Algae (HERB 00124). Morphology. The thalli formed turfs arising from a perennial basal crust, approximately 2–17 cm tall. Upright axes were uniaxial, pseudoparenchymatous, and unstalked, dark green in colour, and slightly curved (Fig. 3 a). The thalli lacked true branches; however, in parts where the axes were broken, young branches developed, which can be described as “ false branches ” (Fig. 3 c). Nodes and internodes were clearly distinguishable (Fig. 3 b). The nodal basal portion varied between 381 and 520 μm, the nodal median portion between 596 and 820 μm, and the nodal apical portion between 320 and 636 μm. The internodal basal portion was 212–380 μm, the internodal median portion was 437–540 μm and the internodal apical portion was 400–485 μm. The nodal to internodal ratio ranged between 1.3 and 1.4. The central axis of the thallus was composed of numerous cortical filaments and radial cells that departed from them, consisting of two layers, the proximal one not touching the outer cortex, and the distal one, Y-shaped, connected to the cortex (Fig. 3 e, f). The thalli were monoecious. In the fertile thalli, the spermatangial sori were arranged in nodal narrow rings, sometimes interrupted (Fig. 3 b), while the carposporophyte was formed on the inner portion of the cortex. The carposporangia were arranged in chains (Fig. 3 d), and each carpospore in the chain ranged between 25 and 30 µm in length and between 20 and 25 µm in diameter. Finally, the sporophyte (Chantransia stage) was observed in several thalli. It appeared reddish to brownish in colour, with alternating and / or unilateral branching (Fig. 3 g). This stage grew near the base of the gametophytic thallus. In one case, the Chantransia stage was observed producing juvenile gametophytes from the branches of its filaments (Fig. 3 h). Ecology and associated species. Paralemanea catenata was found in both investigated sites: Monte San Nicola, characterised by natural rapids created by erosion, and Passo Mojo, an artificial water bridle. In Monte San Nicola, the species shared the same habitat with L. fucina, while in Passo Mojo, it colonised vertical surfaces beneath a small waterfall originating at the end of the concrete bridle. In early July, as the river capacity decreases, the drying up of the surface of certain rocks causes the desiccation of the thalli. During this period, field observations indicated that P. catenata persisted as a perennial crust on the rock substrates (Fig. 4 a). The associated cyanobacteria and macroalgae identified at the two sites were Cladophora sp., Vaucheria sp., and Nostoc sp. At both sites, P. catenata formed extensive populations covering several square meters, becoming the physiognomic dominant, especially in areas with greater exposure to water flow. During summer, when the river capacity is lower and the flow is less turbulent, Cladophora sp. and Vaucheria sp. were observed forming mosaic-like assemblages on surfaces colonised by P. catenata, growing between or above the thalli of this dominant species. In some instances, these taxa completely overgrew the basal crusts of P. catenata following the senescence of the gametophytes (Fig. 4 b).

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