Acta Botanica 2-2015.indd ACTA BOT. CROAT. 74 (2), 2015 245 Acta Bot. Croat. 74 (2), 245–252, 2015 CODEN: ABCRA 25 ISSN 0365-0588 eISSN 1847-8476 DOI: 10.1515/botcro-2015-0020 A new European record of Diadesmis fukushimae and its transference to Humidophila genus (Bacillariophyta) CSILLA KÖVÉR1, JÁNOS KORPONAI1, SÁNDOR HARANGI2, KRISZTINA BUCZKÓ3* 1 University of West Hungary, Faculty of Natural Science, Károlyi Gáspár tér 4. H-9700 Szombathely, Hungary (kover.csilla@ttk.nyme.hu) 2 University of Debrecen, Faculty of Natural Science, Egyetem tér 1. H-4032 Debrecen, Hungary 3 Department of Botany, Hungarian Natural History Museum, Könyves Kálmán krt. 40. H-1476 Budapest, Hungary Abstract – Diadesmis fukushimae, a rare oligotraphenic diatom, was found in some high mountain lakes of Romania. Its occurrence in the Parâng and Retezat Mountains is the second European record of the species. To date D. fukushimae has been known only from the type locality (Shenandoah National Park, Virginia, USA) and from a spring (Grotta Guernica, Dolomiti Bellunesi National Park (south-eastern Alps, Italy). Investigation by scanning electron microscopy showed that this species should be transferred to the re- cently established genus Humidophila. A new combination is proposed, Humidophila fukushimae. The morphological details of the European population are also presented. Keywords: Diadesmis, diatoms, Humidophila, mountain lakes, oligotrophy, taxonomy Introduction During studies on diatom assemblages in high mountain lakes a characteristic species was recently recorded. The heavily silicifi ed diatom at fi rst glance resembles representatives of the genus Diadesmis (GRUNOW 1860: 552), but was not identical to the known and illus- trated European taxa (e.g., KRAMMER and LANGE-BERTALOT 1991, LANGE-BERTALOT and MET- ZELTIN 1996). After detailed investigation we identifi ed it as Diadesmis fukushimae Lange- Bertalot, M. Werum & Broszinski (WERUM and LANGE-BERTALOT 2004). The only previous European record of this diatom has been from the Grotta Guernica spring (Dolomiti Bel- lunesi National Park, south-eastern Alps, Italy) as reported by CANTONATI and SPITALE (2009). * Corresponding author, e-mail: krisztina@buczko.eu KÖVÉR C., KORPONAI J., HARANGI S., BUCZKÓ K. 246 ACTA BOT. CROAT. 74 (2), 2015 Recently, LOWE et al. (2014) published a study on the taxa and populations of the genus Diadesmis, subgenus Paradiadesmis, from the Hawaiian Islands. On the basis of the struc- ture of valves, they concluded that most of the known Diadesmis taxa considerably differ from Diadesmis confervacea Kutzing (1844: 109), which is the type species of the genus Diadesmis. The establishment of a new genus, Humidophila Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bertalot & Kopalová 2014, was necessary and was accomplished by splitting off the genus Humidophila from the genus Diadesmis (KÜTZING 1844) by LOWE et al. (2014). A total of 47 former Diadesmis species were transferred to Humidophila, but Diadesmis fukushimae was not mentioned in this compilation. A species of genus Diade- smis is fairly easily distinguished from other naviculoid diatoms by the combination of striae and raphe structure, and valve shape (ROUND et al. 1990). According to the defi nition of the genus Humidophila (LOWE et al. 2014), the species belonging to the new genus are linear, linear-elliptical to elliptical. The valve face is fl at; a narrow ridge can be seen between the valve face and mantle. Striae on the valve face are composed of one elliptical to ovoid areola. On the valve mantle, one single, elongated are- ola opening is in line with each stria. The raphe is fi liform, straight with variable external proximal raphe endings but never defl ected, bent or hooked. Distal external raphe endings never extend onto the mantle. Internally, areolae openings are covered by a porous hymen. The central nodule is small and rounded. Proximal raphe endings are straight or slightly anchor-shaped; distal raphe endings terminate in small helictoglossae. In AlgaeBase there are 65 records of Diadesmis taxa listed (GUIRY and GUIRY 2014), and 75 species names are found in the California Academy of Sciences Catalogue of Diatom Names (FOURTANIER and KOCIOLEK 2014), which speaks to the richness of this group. Material and methods A total of 40 high mountain lakes, situated in three characteristic mountain regions of Romania: the Făgăraş, Parâng and Retezat Mountains were sampled in 2012, 2013 and 2014. The results of the sampling are under preparation and investigation. The diatom as- semblage analysis is complete but the results have not been published. For analyses of the siliceous algae, samples were prepared using standard digestion pro- cedures (BATTARBEE 1986). Aliquot-evaporated suspensions were embedded in Zrax and Pleurax. Approximately 400 valves were counted from each sample using a light micro- scope (LEICA DM LB2 with 100 HCX PLAN APO objective and VSI–3.OM(H) digital camera). For scanning electron microscope analysis (SEM), cleaned samples were air-dried on an aluminium stub. Coating with gold-palladium was accomplished using an XC7620 Mini Sputter Coater for 120 s at 16 mA. A HITACHI S–2600N scanning electron micro- scope operated at 20 kV and 5–8 mm distance was used. Morphological terminology fol- lows BARBER and HAWORTH (1981) and ROUND et al. (1990). Valve measurements were made from digital images using the camera software. The following samples were used for documentation in this paper: – BP 2013/152; Lake Peleaga, sample from the deepest part of the lake, at 4.1 m water depth, collected on 21st July 2013. – BP 2013/160; Lake Negru, the deepest part of the lake, at 27.2 m water depth, col- lected on 25th July 2013. HUMIDOPHILA FUKUSHIMAE IN EUROPE ACTA BOT. CROAT. 74 (2), 2015 247 Results Diadesmis fukushimae was found in three lakes in the Romanian Carpathians, one in the Parâng Mountains and two in the Retezat Mountains. The localities and some chemical pa- rameters of the lakes where D. fukushimae was detected are shown in Tab. 1. The relative abundance of it was low in all the samples. It was most numerous in Lake Negru, although its relative abundance remained below 3% in this lake. On the basis of the description of Humidophila we should transfer Diadesmis fukushi- mae into this newly defi ned genus. Observation Humidophila fukushimae (Lange-Bertalot, M. Werum et Broszinski) Buczkó and Kövér comb. nov. Figs. 1A–N, Figs. 2A–D, Figs. 3A–D. Tab. 1. Locations and some chemical parameters of the lakes where Humidophila fukushimae was found. Lake Mountain region Altitude (m) a.s.l. N E pH Water depth (m) Conductivity (μS cm–1) Rosiile Parâng 1978 45°20’41,3” 23°33’15,8” 8.54 17.2 12.5 Negru Retezat 2036 45°21’33,2” 22°49’36,6” 7.71 27.7 15.0 Peleaga Retezat 2122 45°21’51,9” 22°54’07,6” 7.51 4.1 13.0 Fig. 1. Humidophila fukushimae: LM micrographs of population on Lake Negru (A–M), valve view (A–L); scanning electron micrograph (SEM), entire frustule in girdle view in oblique posi- tion (N). Scale bar represents 10 μm except for N where scale bar = 5 μm. KÖVÉR C., KORPONAI J., HARANGI S., BUCZKÓ K. 248 ACTA BOT. CROAT. 74 (2), 2015 Basionym. Diadesmis fukushimae Lange-Bert, M. Werum et Broszinski 2001 Diatom 17, pp 6–9, Pl. 1, Figs. 33–38, Pl. 2, Figs. 47–53, Pl. 3. 54–57. Morphological observations Light Microscopy (Figs. 1A–M) Valves are linear-elliptical to elliptical-lanceolate, ends not protracted (Figs.1A–L). Frustules in girdle view are broadly rectangular (Fig. 1M). Valve dimensions (n = 20): length 14–21.7 μm, (x = 17.4 ± 2.2), width 4.5–6 μm (x = 5 ± 0.4), frustule’s width more than 4 μm (Fig. 1M). Raphe is fi liform, straight, with distinct central pores. Axial area is broad, but strongly narrowed and lanceolate to the ends. Transapical striae are very short, and diffi cult to resolve in LM. Fig. 2. Humidophila fukushimae: scanning electron micrograph (SEM), external valve view; valve face and open bands (A); details of the central area with central pores that are entirely fl anked by de- pressions (B), note relief–like patches in the area between raphe and areolae; details of apices with the simple raphe ends (C), note ridge of silica at the junction of valve face and mantle; en- tire frustule (D). Scale bars represent 5 μm for A and D, and for B and C scale bars = 2 μm. HUMIDOPHILA FUKUSHIMAE IN EUROPE ACTA BOT. CROAT. 74 (2), 2015 249 Scanning Electron Microscopy (Fig. 1N, Figs. 2A–D, Figs. 3A–D) Valves are fl at (Fig. 1N, Figs. 2A–D). Junction of the valve face and mantle bears a ridge of silica (Fig. 1N, Figs. 2B–C). Striae are uniseriate, containing round poroids (Fig. 1N, Fig. 2A–D), the number of areolae is 38–40 in 10 μm. The central pores are fl anked by short but comparatively deep depressions (Figs. 2A,B,D). The hymens lie on the inner sur- face of the transapical ribs making the valve interior appear somewhat featureless (Figs. 3A,B; ROUND at al. 1990). Sometimes there are polar excavations on the sternum in the inside view (Fig. 3B). Axial area is broad (Fig. 1N, Figs. 2A–D). Distal raphe endings are Fig. 3. Humidophila fukushimae (A–D) and Humidophila perpusilla (E–G): scanning electron mi- crograph (SEM), internal valve view (A–D); internal overview of an entire valve (A–B), note the not quite T–shaped central raphe endings; the hymens lie on the inner surface of the transapical ribs, partly corroded (B), note the polar excavations (marked by arrow); details of apices with simply raphe endings and intercalated shorter striae (C); details of central part (D); external girdle view (E); valves of an entire frustulum with inside and outside view (F), note the mantle areolae located on the valve face (LOWE et al. 2014); external view of a valve (G). Scale bars represent 5 μm except for D where scale bar = 2 μm. KÖVÉR C., KORPONAI J., HARANGI S., BUCZKÓ K. 250 ACTA BOT. CROAT. 74 (2), 2015 simple (Fig. 3C), proximal raphe endings not quite T-shaped (Fig. 3D). The cingulum con- sists of a few to many open bands (two bands on Fig. 2D, four bands on Fig. 1N), with one transverse row of round poroids (Fig. 1N, Figs. 2A–D). Irregular relief-like patches in the area between raphe and areolae can be observed (Fig. 1N, Figs. 2B–D) but no such struc- tures are seen on Fig. 2A. Intercalated shorter striae are in the apices (Fig. 3C). Taxonomical remarks: The valves of the Carpathian population are markedly smaller (14–21 μm) than is indicated in the description (18–25 μm). The width of the valves – a more stable feature of a species – is 4.5–6 μm (in the type population the width is 5–6 μm). The number of striae is higher (38–40/10 μm) than the 34–36 /10 μm in the holotype popu- lation (WERUM and LANGE-BERTALOT 2000). Another difference, of deep polar excavations on either side of the sternum in the inside view, as documented by LANGE-BERTALOT and WERUM (2001) and WERUM and LANGE-BERTALOT (2004), can be observed only on a few valves; the majority of our population is without such a structure. Humidophila fukushimae is similar in outlines to the most common H. perpusilla (Grunow 1860: 552) (LOWE et al. 2014). However H. perpusilla (Figs. 3E–G) is signifi - cantly smaller. Humidophila perpusilla co-occurred with H. fukushimae in Lake Negru. Distribution: Humidophila fukushimae was originally described in Shenandoah Na- tional Park near »Hogback Overlook«, Virginia, USA. It was collected from a freshwater spring trickling over rocks (leg. Anja Broszinski, November 1999), and was dedicated to Hiroshi Fukushima on the occasion of his 77th birthday (LANGE-BERTALOT and WERUM 2001) in the journal Diatom. Three years later the description with the same photographic docu- mentation was published (WERUM and LANGE-BERTALOT 2004) on page 136, Plate 62 Figs. 33–38, Plate 63 Figs. 1–7, and Plate 64 Figs. 1–4. Recently CANTONATI and SPITALE (2009) published a record away from its type locality, in Europe. They reported H. fukushimae from Spring Grotta Guernica, where this diatom also had very low relative abundance (0.2%), as in our samples. Discussion It is noteworthy that the representatives of genus Humidophila are known from aerial/ subaerial habitats and most of the species were collected from springs and/or wet surfaces. We have found H. fukushimae in mountain lakes, furthermore from the deepest part of the lakes (water depth varied between 4.1 and 27.7 meter). It was the most frequent in a deep lake, Lake Negru. On the other hand, the sample from the lake bottom was rich in silt, per- haps as a result of erosion from the lakeshore, which could be an explanation for the un- usual habitat. The obtained results confi rm the presence of a typical and highly specifi c limnoterrestrial diatom fl ora in the high mountain lakes of the Carpathians. The taxonomic revision of the diatom assemblages of poorly studied regions, such as Antarctica (e.g. VAN DE VIJVER et al. 2011) or Lake Baikal (KULIKOVSKIY et al. 2012), re- vealed a biogeographic pattern of several diatoms; they are not »cosmopolitan« with world- wide distribution, as has been generally accepted for a long time. Our fi nding somewhat contradicts the previous idea, as we found a species whose distribution to date was believed to be restricted to the American continent. Humidophila fukushimae appears to be a peculiar species with regard to its valve out- line and dimensions, and its valve face structure, which enabled us to identify it easily. It HUMIDOPHILA FUKUSHIMAE IN EUROPE ACTA BOT. CROAT. 74 (2), 2015 251 can be considered a rare diatom species, and its discovery in the Carpathians draws atten- tion to how restricted our knowledge of diatom distribution is, even in a well-investigated area like Europe. This new record also highlights the diatom species richness of high moun- tain regions and their importance for diatom biodiversity conservation. Acknowledgements We are very grateful to Rex Lowe for sharing his personal/unpublished data on Diades- mis/Humidophila taxa. We thank the Hungarian Scientifi c Fund for fi nancial support (OTKA 83999). References BARBER, H. G., HAWORTH, E. Y., 1981: A guide to the morphology of the diatom frustule with a key to the British freshwater genera. 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