Cynodontium fallax

Ignatova, E. A., Czernyadjeva, I. V. & Fedosov, V. E., 2024, A new species of Cynodontium (Rhabdoweisiaceae, Bryophyta) from Russia with comments on related species, Arctoa 33 (1), pp. 24-30 : 25-28

Cynodontium fallax

All records of C. fallax from Urals, Altai and Russian Far East mentioned in Savicz-Lyubitskaya & Smirnova (1970) were based on misidentified specimens which we refer to C. asperifolium or C. tenellum (Schimp.) Limpr. We also failed to find any other specimens that can be referred to C. fallax . The combination of mammillae / papillae mainly on adaxial leaf surface and few or none papillae on abaxial one, usually bistratose leaf margins, and straight, cylindrical, furrowed in dry condition capsules makes this species very similar to C. polycarpon (Hedw.) Schimp. They are distinguished mainly by annulus structure: in C. fallax , the annulus is persistent, consisting of small cells, while in C. polycarpon it is revoluble, consisting of 2–3 rows of large, inflated cells. The latter species is rare in Russia, it is represented in herbaria by few collections, mainly with already deoperculate capsules, but we observed an annulus of large cells. Plants the from Russian Caucasus, including those found identical to European specimen in sequences of plastid

and mitochondrial markers ( Fedosov et al., 2021) disagree with the latter species in morphology, therefore they are considered separately.

Cynodontium gracilescens

This species was erroneously reported by Savicz-Lyubitskaya & Smirnova (1970) from the Russian Far East: the only old specimen from Amur River basin in LE actually belongs to C. tenellum . All studied specimens from the Caucasus identified as C. gracilescens possessed straight setae, whereas in most Floras (e.g., Limpricht, 1890; Hallingbäck et al., 2006) C. gracilescens is characterized as having setae cygneous in wet condition. No specimens from the territory of Russia fully fitting the concept of C. gracilescens were found.

Cynodontium asperifolium

This is another species with unistratose leaf laminae and mammillae / papillae in each cell on both surfaces. It was described from southern Siberia (Kuznetsky Alatau Mts.) and was hitherto known only in Russia (Asian part and Urals), Middle Asia ( Kazakhstan and Kyrgyzstan) ( Ignatov et al., 2006), and Mongolia (Tsegmed, 2010). It differs from the Caucasian plants in having leaves with wider acute or occasionally subobtuse leaf apices, cells with lower mammillae, and perichaetial leaves abruptly narrowed into very short acumina. Savicz-Lyubitskaya & Smirnova (1970) describe its stem leaves as ca. 2 mm long, which is considerably shorter than it is observed in most Caucasian specimens. According to our observations, the leaf length of C. asperifolium is more variable and overlap with the Caucasian plants ( Fig. 3 ). Our measurements of leaf length and width confirm that the Caucasuan plants in most cases have longer and wider leaves than C. asperifolium , but in few cases specimens from the Caucasus with smaller leaves, as well as specimens of C. asperifolium with larger leaves were observed ( Fig. 3 ). Newertheless, Mann-Whitney U test indicates the significance of differences between them in both leaf length and width. In unclear cases, the most reliable distinguishing characters between the Caucasian taxon and C. asperifolium are the shape of perichaetial leaves (see Fig. 1 E, G vs. P) and height of mammillae / papillae ( Fig. 1 J vs. Q). There is also a difference in shape of perigonial leaves: they are abruptly constricted into short acumina in the Caucasian plants and obtuse in C. asperifolium ( Fig. 1 I vs. R).

In the molecular phylogenetic analysis in Fedosov et al. (2021), five specimens of C. asperifolium were resolved in a maximally supported clade sister to C. bruntonii , with their joint clade in a sister position to the clade composed of ‘ C. fallax ’ (as it was called there) & C. gracilescens . Thus, a separate status of C. asperifolium and the Caucasian plants in question was confirmed.

Cynodontium species from the Caucasus

The Caucasian specimens erroneously called as S. gracilescens and S. fallax obviously represent the same

K M N O P R

species. It is very similar to C. gracilescens in having high mammillae / papillae in each cell on both surfaces ( Fig. 1 D & J ); however, its leaves have sharply acute apices, whereas they are described and illustrated as usually subobtuse in C. gracilescens (e.g., Lüth. 2019). The Caucasian plants never have setae cygneous when wet or geniculate when dry. Limpricht (1890) also provided an illustration of perichaetium of C. gracilescens (Figure on page 285) showing inner perichaetial leaves abruptly narrowed into very short acumina. Instead, the Caucasian plants always possess more gradually tapered perichaetial leaves with longer acumina ( Fig. 1 G–H ). There is also an evidence from molecular data for separating the Caucasian specimens from C. gracilescens . Previously published molecular phylogenetic analysis based on plastid (trnS-rps 4 and trn L-F) and mitochondrial (nad 5) DNA sequences ( Fedosov et al., 2021) resolved the Caucasian specimens (called C. fallax ) and Central European specimens of C. gracilescens in separate, well supported clades sister to each other.

All other species of Cynodontium and Cnestrum with similar mammillae / papillae on both leaf surfaces possess other morphological traits not allowing referring the Caucasian specimens into any of them. Therefore here we describe these plants as a new species.

Figures

Fig. 3. Stem leaf length, mm (A) and width, mm (B) of Cynodontium caucasicum (left) and C. asperifolium (right). In total, 13 specimens of C. caucasicum and 22 of C. asperifolium were taken, from each specimen five stem leaves were measured.

Fig. 1. A–D: Cynodontium gracilescens (from: [AUSTRIA] Tirolia (Vorarlberg), C. Loitlesberger s.n., Kryptogamae exsiccatae №1071, LE); E–J: C. caucasicum (F–G: from Russia, Kabardino-Balkarian Repub1ic, MW903217; E, H, I: from Russia, Dagestan, MW9111628); K–M: C. fallax (from: Adamstal in Mähren, J. Podpera s.n.: F. Petrak, Flora Bohemiae et Moraviae exsiccate, II Serie, №161, LE); N–R: C. asperifolium (from: Russia, Amurskaya Prov., N, P, Q, R – MW9079345, O – MW9118955). A–B, G– H, K, P: perichaetial leaves; C, F–E, L, N–O: stem leaves; D, J, M, Q: leaf transverse sections; I, R: perigonial leaves. Scale bars: 1 mm for A–C, F–I, K–L, N–P, R; 100 µm for D, J, M, Q.