Vaucheria cf. borealis Hirn, 1900

Muralidhar, Abishek, Broady, Paul A., Macintyre, Duncan P., Wilcox, Michael D., Garrill, Ashley & Novis, Phil M., 2014, Morphological and phylogenetic characterization of seven species of Vaucheria (Xanthophyceae), including two new species, from contrasting habitats in New Zealand, Phytotaxa 186 (3), pp. 117-136 : 124-127

Vaucheria cf. borealis Hirn

Siphons 35–50 µm diameter; branches frequent. Alga monoecious; antheridia and oogonia adjacent, rarely observed ( Fig. 4 ). Antheridia circinate-cylindrical, 50–55 µm long × 20–35 µm diameter. Oogonia ovoid, 60–80 µm long × 55–70 µm diameter; long axes parallel to length of siphons; scarcely stalked with a beak, parallel to length of siphon; oogonial wall evenly textured, smooth. Mature oospores similar in shape but smaller in size to oogonia, a portion of oogonium left vacant by mature oospore.

Section:— Corniculatae.

Representative specimen:— NEW ZEALAND: Canterbury: Cave Stream (43.194954° S, 171.743010° E), A . Muralidhar, 15 October 2010, UCVFW6 ( CHR 631516 ) .

References:— Brown (1929: 94); Hoppaugh (1930: 337); Venkataraman (1961: 71); Reith (1980: 57); Entwisle (1987: 316); Johnson & Merritt (2002: 267).

Molecular data:— This strain was found to be more closely related to the V. bursata strains in our study (maximum p-distance = 0.005) than to a strain designated as V. borealis (Genbank accession JQ967036 ; p-distance = 0.025). There were 4 bp differences over the 706 bp overlapping region between our strain and the V. bursata strain it is closest to UCVFW3. The next closest match was a strain designated as V. repens (p-distance = 0.019).

Notes:— We had difficulty in unequivocally placing this strain under any species in sect. Corniculatae. The presence of just one oogonium per antheridium as opposed to two in V. bursata and the fact that the long axes of the oogonia were always parallel to the length of the siphons rather than oblique, separated it from V. bursata ( Hoppaugh 1930, Venkataraman 1961, Reith 1980). Oogonial orientation also separated another species from our strain — V. repens Hassall (≡ V. sessilis f. repens (Hassall) Hansgirg ), considered a heterotypic synonym of V. bursata in this study and by most authors ( Venkataraman 1961, Christensen 1969, Entwisle 1987, 1988a). In this species, the long axes of the oogonia are at an angle to the siphons ( Hassall 1845, Hoppaugh 1930, Sarma 1974). We found that this strain conformed most closely to published descriptions of V. borealis Hirn ( Hoppaugh 1930, Venkataraman 1961, Reith 1980, Entwisle 1987, Johnson & Merritt 2002, Nemjová & Kaufnerová 2009). The characters which matched it to V. borealis were the ovoid-reniform shape of the oogonia, the long axes of the oogonia always parallel to siphons, mature oospores smaller than the oogonia, smooth texture of oogonial walls. The smaller size of the siphons (35–50 µm diameter) and smaller length and diameter of the oogonia (60–80 µm long × 55–70 µm diameter) were the only characters which did not conform with this species. Hoppaugh (1930) also reported two strains, which conformed closely to the original description of V. borealis Hirn , except for the smaller size of siphons and oogonia. This strain was found to be genetically more closely related to our V. bursata strains than a strain designated as V. repens (see above and Fig. 2 ). It should be noted that Entwisle (1987) found the orientation of the oognonial long axes too variable as a character to distinguish between species in the section. But, after extensive scrutiny of other species descriptions of sect. Corniculatae, this strain has been named Vaucheria cf. borealis , pending further analysis. Oospores in this strain were brown when mature with a prominent reddish colouration towards the center. The base of the oogonial pedicel was also found to be reddish-brown. These characters were obvious in all oogonia. There is no mention of these characters in reports of V. borealis . A comparison of characters of some closely related morphospecies in the sect. Corniculatae is given in Table 3.

This strain grew in Cave Stream, close to the bank, by the entrance to a limestone cave, attached to aquatic plants and other filamentous algae. The field material was fertile. Vaucheria borealis is a rare species which grows on damp soils, in peat bogs and freshwater habitats ( Entwisle 1988a; Johnson & Merritt 2002; Nemjová & Kaufnerová 2009). There are no published records of V. borealis from New Zealand. It has been reported previously from China, USA, Canada, Spain, Czech Republic, British Isles, Finland, Iceland, Norway, Russia, Germany and Austria.

Vaucheria erythrospora Christensen

Siphons 45–65 µm diameter, pale green; branches frequent. Alga monoecious; antheridia lateral to two oogonia borne on a gametophore, more than one gametophore can occur on a single peduncle; gametophores frequent ( Fig. 5 ). Antheridia circinate, 75–80 µm long × 15–25 µm diameter. Oogonia ovoid-reniform, pendent, 80–100 µm long × 50–75 µm diameter. Oospores same shape as oogonia. Mature oospores reddish-brown, break off easily, leave conical distal cavity in oogonia.

Section:— Racemosae ( Walz 1866: 144) Entwisle (1988a: 32)

Homotypic synonym:— Vaucheria hamata f. salina Rieth (1956: 135) .

Representative specimen:— NEW ZEALAND: Canterbury: Saltwater Creek (43.277782° S, 172.696999° E), A . Muralidhar & P. A . Broady, 5 June 2011, UCVBW1 ( CHR 631517 ) .

References:— Christensen (1956: 277); Entwisle (1988a: 34).

Molecular data:— The closest match to our V. erythrospora strain belonging to sect. Racemosae in terms of p-distance, was a strain of the same species collected from a brackish salt marsh in Amager, Denmark (p-distance = 0.031). It clustered with strains of other species in the sect. Racemosae ( V. geminata , V. pseudogeminata Dangeard (1939: 214) , V. prona , V. frigida ( Roth 1797: 166) Agardh (1824: 173) and V. terrestris ( Vaucher 1803: 27) de Candolle in Lamarck & de Candolle (1805: 62); Fig. 2 ).

Notes:— This strain was identified as Vaucheria erythrospora Christensen , based on descriptions by Christensen (1956) and Entwisle (1988a). The field material was fertile. It grew on intertidal sediments of a creek. These were submerged during high tide and exposed during low tide. Salinity of the creek ranged from 2 ppt during low tide up to 35 ppt during high tide ( Muralidhar et al. 2013). This is the first record of V. erythrospora from New Zealand. It is found in terrestrial to semiaquatic habitats of salt marshes and estuaries worldwide.

Figures

FIGURE 2. 50% majority rule consensus tree showing Bayesian phylogenies of Vaucheria strains from different habitats in New Zealand (indicated in bold) based on the phylogenetic analysis of the rbcL gene and partial rbcL-rbcS spacer region. Support numbers and branches are Bayesian posterior probabilities/ Maximum Parsimony bootstrap values. The different taxonomic sections of the strains are as in Andersen and Bailey (2002) and the presence and absence of a gametophore bearing antheridia and oogonia are indicated beside the tree. Scale bar = 0.1 substitutions/site. Substitution model and data sets described in text.

FIGURE 4. Light micrographs and illustration of Vaucheria borealis reproductive structures (UCVFW6).A.Antheridium with developing oogonia. B, C, F. Single ovoid oogonia with a horizontal beak and an evenly textured, smooth wall and a circinate antheridium; note reddish colouration of mature oogonial pedicel in C, D. Mature antheridium. E. Mature oogonium with characteristic reddish oospore, smooth wall, horizontal beak (arrows). Scale bars = 20 µm.

FIGURE 5. Light micrographs and illustrations of Vaucheria erythrospora reproductive structures (UCVBW1).A–D, H. Two pendant oogonia borne laterally on pedicels to 1 circinate antheridium. E, G. Gametophore with a single oogonia; note distal oogonial cavity (arrow). F. Mature oogonia broken off from gametophore, note characteristic red colouration of the oospore and distal oogonial cavity. Scale bars = 50 µm.