Schistidium subconfertum (Broth.) Deguchi was included in the European checklist of bryophytes based on a single specimen from the Italian Alps (‘Grimmia atrofusca. Italien: An der Strasse über das Stilfser Joch auf der Paßhöhe, 26/8 1909, J Glowacki’, GJO 0102803; Hodgetts and Lockhart 2020, Hodgetts et al. 2020). Hans H. Blom determined the specimen back in 1996, thus long before S. succulentum Ignatova & H.H. Blom was described (Ignatova at al. 2010). Consequently, the discovery of S. succulentum in the European Alps (Kiebacher 2020) rose doubts about the identity of the Glowacki-specimen, because S. succulentum likewise has a reduced peristome and share several other sporophytic and gametophytic character states with S. succulentum (Ignatova et al. 2010). To solve the task, we re-examined the Glowacki-specimen morphologically and found that it represents S. succulentum (Fig. 1, 2). Hence, S. subconfertum should be excluded from the list of European species and again represents a taxon to-date solely known from China, Japan and North Korea (Tong and Yuhuan 1998, Gao et al. 2003). The major difference between the two taxa is found in the morphology of the leaves (Table 1). Schistidium succulentum has at least some leaves with a partially bistratose distal lamina, a dorsally strongly projecting and often papillose costa and strongly thickened, 2–4 stratous upper leaf margins. In contrast, according to the descriptions and images provided by Cao and Vitt (1986) and Deguchi (1978), S. subconfertum has an unistratous lamina (except the bistratose margins), and the costa is only shallowly projecting dorsally and smooth. The paracostal basal lamina cells are very long and thin-walled in S. subconfertum, forming somewhat inflated, sharply delimited hyaline areas (windows), whereas they are shorter and with thicker walls, forming much less pronounced areas in S. succulentum. Furthermore, in S. succulentum the upper part of the perichaetial leaves is inclined above the capsule (Fig. 1, 3) whereas in S. subconfertum the perichaetial leaves are more or less straight (Fig. 4). In addition, in S. subconfertum the exothecial cells have distinct corner thickenings (cf. Deguchi 1978) that are absent or indistinct in S. succulentum. Although there are several marked differences between the two species, identification should be carried out with caution due to the great variation in salient characters as leaf papillosity and lamina thickness in S. succulentum and because little is known about variation in S. subconfertum. Indeed, additional collections and molecular studies are needed to understand the relationships and variation in the little known and apparently rare S. subconfertum. In Europe, S. succulentum is unlikely to be mistaken for any other species of Schistidium, because of the reduced peristome which is shared only with few other species, namely S. atrofuscum (Schimp.) Limpr., S. flaccidum (De Not.) Ochyra, S. foraminis-martini Kiebacher, Köckinger & H.H. Blom and S. grande Poelt. Among these, S. atrofuscum and S. grande can be most easily separated by the absence of stomata and S. foraminis-martini by the muticous leaves with rounded apices (versus acute, and at least perichaetial leaves often with short hair point). Schistidium flaccidum is closely related to S. succulentum and may superficially look similar. However, it can easily be distinguished from S. succulentum by the short capsules (up to 1.3 × as long as wide) and the very short rostrum formed as a mamilla. In contrast, S. succulentum has elongate capsules (1.5–1.7 ×) and a distinctly rostrate lid. Another Schistidium-species with a reduced peristome is S. cryptocarpum Mogensen & H.H. Blom, known from arctic parts of Asia and North America. It differs from S. succulentum in the 1 (–2) stratose leaf margins (versus 2–4 stratose) and the campanulate (versus cylindric) capsules.

Figure 1.

Original label (left) and shoot with sporophyte (right) of the specimen of Schistidium succulentum collected by J. Glowacki in the Italian Alps (GJO 0102803). Photos: T. Kiebacher.

Figure 2.

Leaf cross sections of Schistidium succulentum from the Glowacki-specimen (GJO 0102803). Scale: 50 µm. Photo: T. Kiebacher.

During recent field trips we discovered further populations of S. succulentum in the European Alps (Fig. 5). These records represent the first records of the species in France and Switzerland:

France, Hautes-Alpes, St. Veran, ca 500 m SW Refuge De la Blanche, 44°39′49.8″N, 6°56′15.4″E, 2553 m a.s.l., at base of large N-facing rock outcrops, greenschist (probably serpentinite or serpentinised peridotite), 14 Jul 2021, T. Kiebacher 2975 (priv. Herb. T. Kiebacher).

Table 1.

Morphological differences between Schistidium subconfertum and S. succulentum.

Switzerland, Canton of Obwalden, Engelberg, N-slope of Mt Titlis, 46°47′1.2″N, 8°25′17.0″E, 2545 m a.s.l., rock outcrops on W-facing slope, on schist, superficially acidic, 3 Sep 2021, T. Kiebacher 3048 (priv. Herb. T. Kiebacher).

Like in the specimen from the Italian Dolomites (Mt Seceda, 02 Sep 2002, M. Lüth 3925; Kiebacher 2020) and opposed to Russian specimens (Ignatova et al. 2010) leaf papillae were not observed in the specimens from France (Fig. 3) and Switzerland as well as in the Glowacki-specimen. The plants from France and Switzerland even lack distinct papillae on the costa and most leaf laminae have relatively few bistratose spots and striae. Furthermore, the alpine plants, especially the specimen from Switzerland are somewhat glossy (versus dull, according to the original description, Ignatova et al. 2010). However, the other morphological characteristics, especially the reduced peristome, the cylindric urns, the ± thin-walled, mostly short and irregular exothecial cells, the awned perichaetial leaves that largely hide the capsules, the distinctly sinuous lamina cells and the sharply keeled leaves in transverse sections, the strongly thickened margins and strongly projecting costa (except in the specimen from Switzerland) clearly indicate S. succulentum. In plants from Switzerland the costa is generally less strongly projecting dorsally than in the other specimens from the Alps known to date, and the usually distinct leaf cross section with the costa set-off from the lamina (cf. Fig. 2) is evident only in some of the leaves.

Figure 3.

Plant of Schistidium succulentum from the French Alps with the perichaetial leaves that are typically inclining above the capsules (from T. Kiebacher 2975). Photo: T. Kiebacher.

We believe that the deviating characteristics observed in alpine specimens (less papillose lamina and costa, glossiness, p.p. not strongly projecting costa) compared to the original description that is based on specimens from Caucasus and Anabar (Ignatova et al. 2010) are due to phenotypic plasticity, presumably in response to habitat conditions. This has support from the ITS sequences that are identical in specimens from Italy and Caucasus (Kiebacher 2020). However, a certain (genetic) differentiation caused by the isolation of the alpine population of the species cannot be excluded.

Figure 4.

Fertile shoots of Schistidium subconfertum with straight perichaetial leaves and shallowly projecting costae. From isotype specimen in G: Dr. Heinr. Frh. v. Handel-Mazzetti. (Diar. Nr. 1353); G-00046108. Photo: T. Kiebacher.

Figure 5.

Known distribution of Schistidium succulentum in Europe. Previous record (grey circle; Kiebacher 2020) and records presented here (black circles). The record from the border region between Italy and Switzerland was previously referred to S. subconfertum.