Schistidium rivulare Podp.

Schistidium rivulare (Brid.) Podp.

SPECIMEN EXAMINED. — Antarctica. West Antarctic Peninsula, Graham Coast, Cape Pérez, 65°24’27.36”S, 64°05’49.39”W, on rock surface in the short moss turf and cushion subformation, 1.III.2019, Parnikoza & Ivanets 298/19 (KRAM [B-257916]).

Schistidium rivulare is a hydrophytic species forming wide patches or turves on wet or damp rocks and in such sites it was found on Cape Pérez on rock surfaces on a vegetated point in the short moss turf and cushion subformation. With this discovery, the southern limit of the geographical range of S. rivulare was shifted approximately 16 km southward, from Cape Tuxen to Cape Pérez on the south side of Collins Bay, and is now at latitude 65°24’27.36”S on the mainland Graham Coast (Fig. 4).

Schistidium rivulare is a bipolar species which exhibits a boreal-montane panholarctic but disjunct geographical range in the Northern Hemisphere and penetrating into the Arctic in the north and having intermediate altimontane stations in the tropics, including North and Central Andes in the Neotropics and East and Central African mountains. However, the tropical records of this species need careful taxonomic revision because a re-examination of some specimens named S. rivulare revealed that they represented different species. For example, the Peruvian material so-named (Deguchi 1987) actually represents two distinct species, S. rivulariopsis (R.S.Williams) Ochyra and S. deguchianum Ochyra & Bedn. -Ochyra (Ochyra & Bednarek-Ochyra 2011). The same proved to be true with the Colombian and Kenyan records of S. rivulare which are actually S. rivulariopsis (Ellis et al. 2015, 2016c), and taxonomic re-evaluation made the latter a typical Afro-American disjunct species (sensu Ochyra et al. 1992; Bednarek-Ochyra et al. 1999; Ochyra & Ireland 2004, 2016; Ochyra & Singh 2008; Bednarek-Ochyra & Ochyra 2010, 2012a, b, 2013a; Ochyra & van Rooy 2013).

In the Southern Hemisphere the most problematic is the occurrence of Schistidium rivulare in Australia and New Zealand. The record of this species in Australia is based on the conspecificity of S. flexifolium (Hampe) Ochyra with S. rivulare (Dixon 1926; Bremer 1980), but these species have little in common with each other, except for being aquatics, and are distinct species (Ochyra 2003). Fife (2000) recognised S. rivulare in the moss flora of New Zealand but his detailed description and illustrations of the plants clearly show that the New Zealand material in fact represents a different species which exhibits some similarity to southern South American and subantarctic S. falcatum (Hook.f. & Wilson) B.Bremer. On the other hand, Fife (2000) distinguished S. rivulare subsp. subflexifolium (Müll.Hal.) Fife, which is clearly conspecific with S. flexifolium (Ochyra 2003). Until detailed taxonomic study of this complex is completed for Australasia, occurrence of S. rivulare in this region should be treated with reservation.

Schistidium rivulare does occur in the Western Hemisphere in Tierra del Fuego (Cardot & Brotherus 1923) and on subantarctic South Georgia (Bell 1984) and penetrates to the maritime Antarctic (Ochyra et al. 2008a) (Fig. 4). In this biome the species is very rare in the South Sandwich Islands and locally frequent on Signy Island in the South Orkney Islands. It is quite frequent on Livingston Island and very rare on King George Island in the South Shetland Islands (Ochyra 1998a), although in the latter island it seems to have spread in recent decades and a large population of this species was found in 2018 on Creeping Slopes above Demay Point and in additional streams in the Point Thomas area in Admirality Bay (Wierzgoń, personal observations) where it was not recorded in the very early 1980s (Ochyra, personal observations). Likewise, S. rivulare is very rare and localised on the Danco Coast and in the offshore Palmer Archipelago and on the Graham Coast where until recently it was collected only on Petermann Island and Cape Tuxen. The present discovery on Cape Pérez is its southernmost record in the Southern Hemisphere.

Outside the Antarctic and South Georgia, in the austral polar biome Schistidium rivulare is known from two subantarctic archipelagoes in the South Indian Ocean, namely Îles Kerguelen (Blockeel et al. 2009a) and Îles Crozet (Ellis et al. 2020b). Thus, it exhibits an amphiatlantic distribution pattern which is typical of many bryophyte species (e.g. Ochyra &Váňa 1989; Bednarek-Ochyra & Ochyra 1998; Ochyra & Lewis Smith 1998; Ochyra & Zander 2002; Blockeel et al. 2007, 2009b; Li et al. 2009; Ochyra 2010; Ochyra & BednarekOchyra 2013; Ochyra et al. 2015).

Schistidium Bruch & Schimp. is the largest moss genus in the Antarctic, consisting of 13 species, of which S. rivulare is the only species occurring outside the Southern Hemisphere. All remaining congeners are austral species and seven of them are Antarctic endemics. Five of these, including S. steerei Ochyra (Ochyra 1987), S. halinae Ochyra (Ochyra 1998b), S. lewis-smithii Ochyra (Ochyra 2003), S. deceptionense Ochyra, Bedn. -Ochyra & R.I.L.Sm. (Ochyra et al. 2003a) and S. leptoneurum Ochyra (Ochyra 2004), are restricted in their occurrence to the maritime Antarctic, whereas the other two, S. urnulaceum (Müll.Hal.) B.G.Bell (Ochyra 1990a) and S. antarctici (Cardot) L.I.Savicz & Smirnova (Ochyra et al. 2008a), are pan-Antarctic species weakly penetrating to subantarctic South Georgia.