Humidophila, Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bertalot et Kopalova, 2014

Furey, Paula C., Manoylov, Kalina M. & Lowe, Rex L., 2020, New and interesting aerial diatom assemblages from southwestern Iceland, Phytotaxa 428 (3), pp. 173-208 : 179-192

Humidophila

Humidophila taxa commonly occurred in association with bryophytes and/or lichen on the euaerial habitats in Iceland (absent only from two sites sparse in diatoms; WW 39 and 21). Of the seven species present, 50% or more co-occurred together, altogether often contributing>50% to the relative abundance of taxa present. Within these, H. gallica ( Smith 1857: 11) Lowe, Kociolek, You, Wang et Stepanek (2017: 281) and H. perpusilla contributed the most to relative abundance. The checklist of algae from Iceland ( Hallgrímsson 2007) lists several Diadesmis Kützing (1844: 109) and Humidophila taxa from aerial environments including those recorded here, such as H. biceps , H. contenta (Grunow in Van Heurck 1885: 109) Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bertalot et Kopalová (2014: 357), H. gallica , and H. perpusilla . We describe one Humidophila species new to science, present information for another unidentified Humidophila taxon, and propose the transfer of Diadesmis contenta var. biceps to Humidophila biceps .

Humidophila sp. 1 (LM = Fig. 8 N–O; SEM = Fig. 8 P–Q)

Description:—The raphe is filiform and continuous from the central area to the end of the row of areolae. Lateral depressions flank proximal raphe ends. Distal raphe ends appear to lack lateral depressions. Axial area is lanceolate. Valves are naviculoid tapering to rounded ends. There is a subtile construction near the ends of the valves. The striae are continuous through the length of the valve and flair in the center leaving a circular central area. We were not able to view specimens with SEM in girdle view nor valve interior.

Collection Information:— ICELAND. Scrape and a bryophyte and lichen squeeze, collected from a rock outcrop in the Hengill watershed (~ N 64 3 23.0, W 21 17 1.0, WW 5 Table 1), P.C. Furey, 13 July 2013. (Cleaned material –GCAC4212, and representative specimen circled on slide GCAC4212 deposited in the diatom collection at Georgia College and State University, USA. Here illustrated as Fig. 8 N).

Comments:—This unidentified taxon should be compared to Humidophila arctica (Lange-Bertalot et Genkel 1999: 40) Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bertalot et Kopalová (2014: 357) but differs in the valves being more naviculoid. Both taxa have areolae that are interrupted in the central area, but frustules of H. arctica have broadly rounded ends ( Lange-Bertalot & Genkal 1999, Tafel 21 Figs 8 –14) in contrast to the more tapered ends of Humidophila sp. 1 . More information, especially around interal and girdle views are needed to establish details key to a new taxon description, therefore, we currently designated this taxon as unidentified Humidophila sp. 1 until more information can be gathered.

Specimens were generally absent from most samples, but occasionally contributed <5% to the relative abundance at sites in Hengill and Þingvellir rift valley, though at WW5 relative abundance reached 5.5% ( Table 2).

Humidophila eldfjallii sp. nov. (LM = Fig. 8 E–H; SEM = Fig. 8 A–D)

Description:—Valves strongly triundulate, length 12.2–14.9 μm, width middle 3.0–3.6 μm, width apices 3.0–3.6 μm; 33.0–35.4 striae in 10 μm (for n=5 LM, n=5 SEM). The raphe is filiform with distal ends bending slightly in opposite directions. The axial area is lanceolate leading to a round central area. Both distal and proximal raphe ends lack any lateral depressions.

Holotype:— ICELAND. Surface scrape and a bryophyte and lichen squeeze collected from a rock face located river right of the River Hengladalsá in the Hengill watershed (~ N 64 3 23.0, W 21 17 1.0, WW 38 Table 1), P.C. Furey, 14 July 2013. Circled specimen on slide GCAC4213 , deposited in the diatom collection at Georgia College and State University Natural History Museum, USA. Here illustrated as Fig. 8 F).

Type Material:—Cleaned type material deposited in the Georgia College and State University Natural History Museum, USA diatom collection. GCAC 4213.

Etymology:—This specific epithet refers to the Icelandic word for ‘volcano’–‘eldfjall’ (eldur–“fire”, and fjall –“mountain”) after the volcanic rock it was collected from in the Hengill watershed; also the location of the Hengill volcano.

Comments:—The strongly triundulate valves of H. eldfjallii are different than most species in this genus. Humidophila eldfjallii differs from H. costei (Le Cohu et Van de Vijver 2002: 122) Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bertalot et Kopalová (2014: 357) and H. ingeae (Van de Vijver in Van de Vijver et al. 2002: 338) Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bertalot et Kopalová (2014: 358) by valves that are much more strongly triundulate with bulbous valve ends, whereas H. costei and H. ingeae have more subtly undulated valves. Additionally, H. ingeae displays marginal aereola on the valve face while they are on the mantle in H. eldfjllii .

Specimens occurred at>5–10% (WW 38) and>10–20% (WW 54) relative abundance in Hengill, but otherwise occurred at low relative abundances in Hengill and the Þingvellir rift valley ( Table 2).

Humidophila parallela ( Petersen 1928b: 15) comb. nov. (LM = Fig. 7 M–O; SEM = Fig. 7 P)

Basionym: Navicula contenta var. parallela Petersen (1928b : Dansk Bot. Arkiv, p. 15, fig 2)

Synonym: Diadesmis contenta var. parallela ( Petersen 1928b: 15) Spaulding in Spaulding et al. (1997: 410).

Valve dimensions (for n=9 LM, n=3 SEM) length 7.2–9.1 µm, width middle 2.0–3.1, width apices 2.0–3.1; 34.0–34.9 striae in 10 µm. T-shaped depression of the proximal raphe ends absent.

This species was earlier considered to be a variety of Navicula contenta Grunow in Van Heurck (1885: 109), and was moved (as a variety) to Diadesmis contenta (Grunow 1885: 109) D.G.Mann in Round, R.M.Crawford & D.G.Mann (1990: 666), but SEM views in this study show that it lacks the T-shaped depressions at the proximal raphe ends, a characteristic of D. contenta . Diadesmis arcuata (Heiden in Heiden et Kolbe 1928: 628) Lange-Bertalot in Moser, Lange-Bertalot et Metzeltin (1998: 136) lacks this depression, and therefore we consider this species to be more closely related to D. arcuata than to D. contenta . There is currently some question about the validity of D. arcuata , as it has a basionym that is illegitimate ( Navicula arcuata Heiden in Heiden et Kolbe 1928: 628) because it was a later synonym of Navicula arcuata Pantocsek (1892: 64 (1905), pl. 6: fig. 97). Lange-Bertalot correctly considered the name arcuata available for a species in Diadesmis , but he incorrectly made a new combination with Heiden’s illegitimate taxon as basionym when he should have simply used arcuata as a replacement name ( Moser et al. 1998). Lowe et al. (2014) made the same error in their new combination. Given that the recognition of subspecific taxa in diatoms is a less widespread practice than in prior decades, and the possible incorrectness of the recent combinations with Navicula arcuata , we decided to recognize this taxon at the species level.

Valves generally were absent or contributed <2% to the relative abundance of samples from Hengill and Þingvellir rift valley, though relative abundance reached 7% at one site in Hengill (WW 3; Table 2).

Humidophila biceps (Grunow in Van Heurck 1880: expl. Pl. XIV, fig. 31B) comb. nov. (LM = Fig. 7 C–E; SEM = Fig. 7 A–B).

Basionym: Navicula trinodis var. biceps Grunow in Van Heurck 1880: expl. Pl. XIV, fig. 31B

Valve dimensions (for n=14 LM, n=4 SEM): length 10.0–14.5 µm, width middle 2.5–3.5 µm; 39.3–41.6 striae in 10 µm. Valves had a slight convex area in the middle. Short, comma–like depressions flanking the proximal raphe ends were similar to those shown in SEM micrographs in Veselá & Johansen (2009, as Diadesmis biceps fig. 199). This taxon is synonymous to D. biceps G.A. Arnott ex Cleve (1894: 132) nom. inval. and D. contenta var. biceps .

Frustules occurred at low relative abundance at several sites in the Hengill watershed, but also reached higher relative abundances at sites in both Hengill and the Þingvellir rift valley, four of which were>20% relative abundance ( Table 2).

Humidophila gallica (W. Smith 1857: 11) Lowe, Kociolek, You, Wang et Stepanek (2017: 281) (LM = Fig. 9 E–J; SEM = Fig. 9 A–D)

The valve dimensions of H. gallica measured at length 9.5–15.0 µm, width middle 3.0–4.2 µm, and 30.8–32.7 striae in 10 µm (for n=11 LM, n=9 SEM). The chain-forming morphology with spines and the absence of a raphe occurred over forms with a raphe but not spines ( Cox 2006). Some populations contain valves predominantly on the shorter side ( Fig. 9 I–J)

Humidophila gallica , consistently present in the Hengill and the Þingvellir rift valley, consistently occurred at relative abundances>5 %, and at 5 sites>20% ( Table 2). Humidophila gallica is a typical on mosses and ferns (as Diadesmis gallica ; Roldán et Hernández–Mariné, 2009).

Humidophila paracontenta (Lange-Bertalot et Werum in Lange-Bertalot & Genkal 1999: 41) Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bertalot et Kopalová (2014: 358) (LM = Fig. 8 I–L; SEM = Fig. 8 M, R–S)

Valve dimensions (for n=8 LM, n=4 SEM): length 9.8–14.4 µm, width middle 2.2–3.8 µm, width apices 2.5–4.3 µm; 28.5–31.2 striae in 10 µm. Short, comma-like depressions flanked the distal and proximal raphe ends (similar to those shown in H. paracontenta var. magisconcava (Lange-Bertalot) Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bertalot et Kopalová (2014: 358) –Pl 65, 3–7 in vol. 13, Werum & Lange-Bertalot 2004).

Humidophila paracontenta , absent from Þingvellir rift valley, typically comprised <1% of the relative abundance of samples from Hengill, but was the only taxon observed from a sparse sample at WW 21 ( Table 3).

Humidophila perpusilla ( Grunow 1860: 552) Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bertalot et Kopalová (2014: 358) (LM = Fig. 7 F–I; SEM = Fig. 7 J–L)

The valve dimensions of H. perpusilla measured at length 8.0–18.1 µm, width middle 3.4–4.6 µm, and 32.3–36.0 striae in 10 µm (for n=25 LM, n=9 SEM). This taxon, very common at sites from Hengill and the Þingvellir rift valley, occurred at>20 % relative abundance at 9 sites ( Table 2).

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