Kyrtuthrix huatulcensis León-Tejera, González-Resendiz & Johansen, 2016

León-Tejera, Hilda, González-Resendiz, Laura, Johansen, Jeffrey R., Segal-Kischinevzky, Claudia, Escobar-Sánchez, Viviana & Alba-Lois, Luisa, 2016, Phylogenetic position reevaluation of Kyrtuthrix and description of a new species K. huatulcensis from Mexico´s Pacific coast, Phytotaxa 278 (1), pp. 1-18 : 8-13

publication ID	https://doi.org/ 10.11646/phytotaxa.278.1.1
persistent identifier	https://treatment.plazi.org/id/C33B5556-FF85-FFFB-3CF2-63E9FC7CFEA6
treatment provided by	Felipe
scientific name	Kyrtuthrix huatulcensis León-Tejera, González-Resendiz & Johansen
status	sp. nov.

Treatment

Kyrtuthrix huatulcensis León-Tejera, González-Resendiz & Johansen sp. nov., Figs. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 .

Diagnosis: —Most similar to K. maculans , from which it differs in having a stratified sheath, thinner thalli, thinner trichomes, and shorter cells ( Table 1). Differing from K. dalmatica by its epilithic habit and stratified sheath ( Table 1). Differing from both species in the absence of false branches and thalli and smaller cell dimensions ( Table 1).

Description:—In natural populations—thalli blue-green, crustaceous, flat, soft, forming neatly delimited and commonly abundant freckle or mole-type colonies 0.5 to 1.0 cm in diameter, less frequently forming longer mat-like colonies up to a few centimeters long, 60–80 μm high. Filaments arranged in tight parallel series, isopolar, forming sharply bent loops in the lower part ( Fig. 1 A, B, D, F View FIGURE 1 ), with distal ends always directed and attenuated towards the upper part of the thallus ( Fig. 1 A, C, E View FIGURE 1 ), to 60 μm long from the basal loop to the terminus. Colonial mucilage firm, generally colorless ( Fig. 1 E–G View FIGURE 1 ), but sometimes yellowish or brownish in the upper surface of the crust ( Fig. 1 A View FIGURE 1 ), lamellated ( Fig. 1 H View FIGURE 1 , Fig. 2 A, B, H View FIGURE 2 ), maintaining the integrity of crustose thalli in intertidal populations subject to battering waves at high tide and drought at low tide. Individual sheaths enclosing and binding both parts of a single bent trichome, producing an evident external layer for each paired portion of a single trichome ( Fig. 1 H View FIGURE 1 , 2 H View FIGURE 2 , 3 C, H View FIGURE 3 ), embedded in the common mucilaginous matrix ( Fig. 3 A–C, H View FIGURE 3 ). Trichomes constricted at cross walls ( Fig. 2 A–G View FIGURE 2 ), (1.2) 2–3 (5) μm wide. Cells variable in form, commonly cylindrical or subspherical, sometimes having the shape of a truncated cone, or extremely irregular with different values of length and diameter within a single cell ( Fig. 1 B–F View FIGURE 1 . Fig. 2 B, C, D, E View FIGURE 2 ), (1) 1.5–3 (6.) μm long. Hormogonia isopolar or heteropolar ( Fig. 3 D–G, L View FIGURE 3 ), liberated through the upper surface, after release soon becoming bent and somewhat attenuated before heterocytes are differentiated ( Fig. 1 G View FIGURE 1 . Fig. 2 A, B View FIGURE 2 . Fig. 3 F–G, K View FIGURE 3 ). Heterocytes solitary, intercalary, mostly cylindrical to quadrate, 1.8–3.1 μm in diameter ( Fig. 1 B–E View FIGURE 1 ), shorter to longer than wide ((1.5) 3–4 (10) μm long); near the apices and sometimes after release of attenuated trichome segments (heteropolar hormogonia) have subspherical shape, 3 μm in diameter ( Fig. 2 C–F View FIGURE 2 ).

In cultures (C708, C695)—thalli soon (1–2 weeks) losing typical parallel disposition of filaments ( Fig. 3 A–B View FIGURE 3 ). Hyaline sheaths surrounding single trichomes difficult to distinguish, gelatinized, remaining evident around pairs of trichomes ( Fig. 3 A–C, H View FIGURE 3 ). Trichomes contorted, conserving constricted cells of a wide range of cell shape and sizes (3–10 μm wide), terminally attenuated ( Fig. 3 A, C–D, G View FIGURE 3 ). Hormogonia commonly short, one to few-celled (4–10 μm long), straight or curved or folded, attenuated or not ( Fig. 3 D–G View FIGURE 3 ). Cells with big pigmented granules ( Fig. 3 A–H View FIGURE 3 ).

Notes on hormogonial development: —Occasionally segments of trichomes become detached, mainly in the upper part of the thalli, and then appear heteropolar. These are likely attenuated hormogonia prior to liberation ( Fig. 3 I View FIGURE 3 ). Other hormogonia appeared to be isopolar ( Fig. 3 E View FIGURE 3 in culture, 3 L), possibly produced below a heteropolar hormogonium, or as the posterior stage of a heteropolar hormogonia after detachment of the attenuated part. Evidence of these types of hormogonia was found in field material; some were straight and others curved, but all were several cells in length. In culture curved cells were seen from a one-celled stage to several-celled segments. Culture conditions likely cause the physiological response for attachment to a substratum to occur earlier. In some instances truncated cone cells in contact with other cells favors fragmentation and the subsequent detachment of a hormogonium, due to the presence of nodes with narrower points of contact between cells ( Fig. 3 F View FIGURE 3 ).

Holotype here designated:— FCME-PTM! C708 deposited in the herbarium FCME-C Facultad de Ciencias , UNAM, preserved in 4% marine formaldehyde with dry material duplicate.

Isotypes: — FCME! material included in C695, C700. Monoclonal population of the reference strain used for molecular data was originated from C708. Additional reference materials are samples PTM 6300, PTM-C59/C61/ C707/C1319/ C1339/C1340/C1341.

TYPE LOCALITY: Mexico. Oaxaca: Supralittoral zone of San Agustín Bay, Huatulco, 15° 41’ 17.41” N, 96° 14’ 15.28” W, August 2014.

Etymology:—Named for the Huatulco region, a natural reserve zone of great biological diversity, from which the species was collected.

Habitat:—Supratidal and intertidal fringes; epilithic on granitic rock. Some supratidal populations exposed, others partially shaded by rock or other Cyanoprokaryotes. Intertidal populations exposed to insolation and various conditions of humidity.

Occurrence:— MEXICO. Oaxaca: Barra Santa Elena 15° 44’ 00” N, 96° 46’ 48”W, September 1997 H. León-Tejera ( PTM 6300 ) GoogleMaps ; San Agustín Bay 15° 41’ 17.41” N, 96° 14’ 15.28” W, December 2010, October 2012, August 2014 L. González-Resendiz & H. León-Tejera (C59, C61, C695, C700, C707, C708) GoogleMaps ; Cacaluta Bay , 15° 43’ 09.00” N, 96° 09’ 59” W August 2014 H. León-Tejera L. & González-Resendiz (C1319) GoogleMaps ; Panteones beach at Puerto Angel , 15° 39’ 50.00” N, 96° 29’ 43.93” W, August 2014 González-Resendiz & H. León-Tejera (C1339, C1340, C1341) GoogleMaps .

Phylogenetic analyses:— K. huatulcensis clearly belongs to the Rivulariaceae ( Fig. 4 View FIGURE 4 ). This clade contains tapering heterocytous forms that in our analysis are all marine in origin. This clade had good support (92/98/0.63, MP/ML/BI, respectively). Rivulariaceae in its historical sense includes Calothrix ( Komárek et al. 2014) , but in our analysis the clade that includes both marine Rivulariaceae and Calothrix is not supported (-/-/0.55), even though Calothrix is shown in a position sister to the Rivulariaceae . However, regardless of the eventual circumscription of the Rivulariaceae , we have clear evidence from the molecular data that Kyrtuthrix belongs in the Rivulariaceae sensu stricto, and certainly is not in the Scytonemataceae , Stigonemataceae or Mastigocladaceae (= Hapalosiphonaceae in modern taxonomy, see Komárek et al. 2014) as proposed by earlier workers ( Ercegovic 1929a, Umezaki 1958, Komárek & Anagnostidis 1989, Komárek 2013). The taxonomic identity of some of the strains in our clade designated “ Rivulariaceae ” is uncertain. There is apparent confusion in differentiation of Calothrix , Rivularia , and Microchaete . The strains in the three lineages labeled “Marine Rivulariaceae I, II and III” are based on our material, and they correspond morphologically to “ Brasilonema ” (MR I) and “ Scytonematopsis ” (MRII and MRIII), both of which are very morphologically dissimilar to Rivularia ( Fig. 4 View FIGURE 4 ). This clade likely has undescribed species and genera within it, and highlights the need for sequence data for a morphologically well-established European population of the type species of Rivularia , R. dura Roth ex Bornet et Flahault (1887: 347) , so that the other morphologically similar but phylogenetically distinct genera can be properly classified.

The strain of K. huatulcensis had 16S rRNA genetic identities of 98% based on p-distance determinations ( Table 2) to Marine Rivulariaceae I, Marine Rivulariaceae II , Calothrix ANT.LPR 2.4, and Calothrix BECID 14, and M. grisea . These taxa are scattered throughout the Rivulariaceae clade, and in order to consider them the same genus, the entire morphologically disparate clade of Rivulariaceae would need to be placed in a single genus ( Rivularia ?). Since we know a number of these taxa and the morphological differences that separate them, we find this conclusion untenable. Examples of genera in the Nostocales that have genetic identities>98% are known ( Flechtner et al. 2002, Kaštovský et al. 2014). The genetic identities do support our conclusion that Kyrtuthrix belongs in the Rivulariaceae and not to other families ( Fig. 4 View FIGURE 4 ), such as the Scytonemataceae ( Table 2).

16S–23S ITS structure analysis: —The secondary structure of the conserved regions of the ITS for K. huatulcensis were most similar to those for strains representing Marine Rivulariaceae I (MRI) and Marine Rivulariaceae II and III (MRII, MRIII) in the phylogenetic analysis ( Fig. 4 View FIGURE 4 ). This was unusual given that these strains appeared more phylogenetically distant based on both the phylogenetic analysis and morphology than the possibly phylogenetically closer strains Rivularia PCC 7116 and Microchaete grisea CCAP 1445 . The D1-D1’ helices in K. huatulcensis were identical in structure to those for MRI and MRII, but differed markedly from PCC 7116 and CCAP 1445 in both the structure of the apices of the helices and the presence of the A-AA mismatch near the base of the helices ( Fig. 5 A–E View FIGURE 5 ). The Box-B helices were similar in sequence in the base, but differed markedly in sequence and length for all five taxa in our comparator group ( Fig. 5 F–J View FIGURE 5 ). The V2 helices were even more divergent in sequence and structure among the five taxa, although it was clear that K. huatulcensis had sequence and structural commonalities with MRI that demonstrated possibly recent phyletic separation ( Fig. 5 K–O View FIGURE 5 ). The V3 helix was also divergent in the five strains, with that of K. huatulcensis being very distinct in nucleotide sequence and structure. It is interesting that Kyrtuthrix showed greatest similarity to MRI and MRII. MRI morphologically is most similar to “ Brasilonema ”, although it is marine in origin, while MRII and MRIII morphologically are closest to “ Scytonematopsis ”. Both of these taxa are very morphologically distant from Kyrtuthix ( González-Resendiz et al. 2015).