R. J. Flower

The distribution and classification of the problematic Fragilaria (Virescens v.) exigua Grun.Fragilaria exiguiformis (Grun.) Lange-Bertalot: a new species or a new genus?

The nomenclature of the taxon first recorded as Fragilaria (virescens) v. exigua by Grunow in Cleve & Moeller (1878) is examined with regard to the current botanical name, F. exiguiformis Lange-Bertalot. The distribution of this taxon in relation to pH is described from surface sediment samples collected from more than 200 soft-water lakes in both NW Europe and Antarctica. The optimum pH requirement is shown to be different in the two regions with a lower optimum (pH 5.7) for the European data set. One reason for this difference is the lack of moderately acid sites in the Antarctic data set. Another is that SEM investigation of F. exiguiformis from several localities shows that at least two taxa, characterized inter alia by presence or absence of spines, are present within this species. Lack of a rimoportula indicates that taxa in the F. exiguiformis complex should be transferred elsewhere. Also, the recognition of a non-spinose taxon within F. exiguiformis indicates that a new species description is requ...

A taxonomic and ecological study of diatoms from freshwater habitats in the Falkland Islands, South Atlantic

1. The diatom flora of the Falkland Islands was investigated by sampling twenty-eight representative lake, pond and stream habitats. Diatom assemblages were moderately diverse and dominated by benthic taxa characteristic of oligotrophic soft waters. 2. Particularly the Fragilarioid and Achnanthoid taxa possessed unusually small valves and this condition is thought to be favoured by the prevailing harsh environmental conditions. 3. Eleven new diatom taxa are described and several new combinations are proposed but it is likely that further research will show that at least some of the new taxa will co-occur, in Patagonia and elsewhere, rather than be endemic in the Falklands archipelago. 4. Taxon richness varied strongly between sites but only weak trends were indicated between total number of taxa, number of regional endemic taxa, or rare taxa and habitat complexity, habitat size or water pH (diversity models were not used because dispersal and immigration rate data are lacking). 5. Cosmopolitan taxa were most common but a significant portion (approximately one third) of the assessed flora was attributed to taxa with regionally restricted distributions. Southern South American, Subantarctic and North American elements were present but probably very few taxa are entirely restricted to the Falkland Islands. 6. Macro- and microecological factors determine both the composition and numbers of taxa in a diatom sample. The species assemblages recorded are thought to reflect near pristine aquatic conditions at all the Falkland sites (palaeolimnogical techniques are nevertheless required to test hypotheses about native and non-native taxa). 7. Irrespective of difficulties in fitting diatom data to species diversity models, the occurrence and abundance of diatom taxa in these representative samples provide a unique site-specific biological signature that reflects water quality and physical habitat as well as regional flora attributes. 8. Routine diatom analysis for ecological purposes requires accurate taxonomy and consistency is of paramount importance but, compared with biogeographic and systematic studies, a lower level of precision is probably adequate. 9. Monitoring diatom communities offers one way of perceiving environmental change and global warming is thought to pose the greatest threat to the biological integrity of the inland waters of the Falkland Islands.

TAXONOMIC DESCRIPTIONS AND OCCURRENCES OF NEW ACHNANTHES TAXA IN ACID LAKES IN THE U.K.

A new species of Achnanthes, A. scotica, is described from Lochnagar in the Cairngorm Mountains, Scotland. Three new varieties, A. altaica v. minor, A. austriaca v. minor, and A. austriaca v. alpina and one new form, A. marginulata f. major, are also described from sites in the Cairngorms and elsewhere. Modern and fossil distributions of these taxa in acid upland oligotrophic UK lakes are evaluated.

A NEW SPECIES OF EUNOTIA, E. PIRLA SP. NOV., FROM WOOLMER POND, AN ACID POOL IN THE SOUTHEAST OF ENGLAND

A new species of Eunotia, E. pirla, is described from the epiphyton in Woolmer Pond, a strongly acid pool in Hampshire, England. The species is illustrated by drawings and light and scanning electron micrographs. E. pirla is considered to be conspecific with Eunotia species 19, described from two acid lakes in Michigan, U.S.A. (PIRLA 1986). Eunotia pirla is thought to be acidobiontic. The relative importance of possible factors influencing intraspecific morphological variation in the Woolmer Pond population is briefly discussed.

PUOCAENICUS TAXA IN MODERN AND FOSSIL MATERIAL MAINLY FROM EASTERN RUSSIA

Pliocaenicus taxa living or in very recent sediments from upland lakes around Lake Baikal are examined in relation to those found in Pleistocene and Miocene deposits in Kamchatcka and elswehere. The validity of the genus Pliocaenicus is substantiated and subdivision of P. costatus sensu lato is examined in some detail. Re-examination of material from Skabitchevskys type locality and an LM and SEM study of conspecific and closely related taxa has been undertaken. Skabichevskys type material is unavailable and two morphotypes have been described in the literature under this epithet. The taxonomy of P. costatus var. sibiricus (Skabitch.) Round & Hakansson is now clarified and a new variety, P. costatus var. leprindus, is established. Comparison with fossil material shows that P. costatus taxa are very stable over time with morphologies differing only in detail of valve central area, areolar density, valve central area texture (colliculate or smooth), spacing of marginal costae, and number of central area f...

The structure and significance of early Holocene laminated lake sediments in the Faiyum Depression (Egypt) with special reference to diatoms

Lake Qarun lies in the Egyptian Faiyum Depression and is the modern remnant of a much larger Holocene lake. Variations in water level occurred during the Holocene as a result of palaeoclimate changes and, since ca. 4000 bp, there have been hydrological interventions. Past lake levels have been inferred from the locations of archaeological sites, former beaches and exposed lake sediments, but there is no continuous Holocene palaeolimnogical record for the lake. To explore the potential of this record, three sediment cores (10.4–21.4 m long) were collected from terrestrial locations on the southern margin of the lake in 2008. The basal sections of all three cores consisted of thinly laminated diatom marl sediments overlying coarse sand. The nature of these laminations was investigated in thin sections from two cores (QARU9 and 10). Quantitative very high-resolution diatom analysis revealed seasonal succession patterns of Aulacoseira and Stephanodiscus species within diatom-rich laminae. Elemental microprobe analysis of one thin section (QARU10) confirmed the presence of alternating Ca- and Si-rich laminae. The results indicate annually deposited sediment sequences with seasonality signals provided by microlayers of diatoms, calcite and clastic material. According to diatom counting, mean varve thicknesses equated to 6.0 (QARU9) and 9.4 (QARU10) annual diatom laminae accumulated cm−1. Radiocarbon dates from a third core (adjacent to QARU9) indicated that the QARU9 thin section material was bracketed between 8693 and 9935 cal bp. Diatom microstratigraphy was used to infer seasonality in varve forming processes. Gross sediment stratigraphy indicated that varve forming conditions had persisted for>1500 years. The presence of early Holocene varved sediments in palaeo-Lake Qarun provides an exceptional palaeoenvironmental archive for northeast Africa.

A NEW VARIETY OF TABELLARIA BINALIS (EHRENB.) GRUN. FROM SEVERAL ACID LAKES IN THE U.K.

A new variety of Tabellaria binalis (Ehrenb.) Grun. var. elliptica, is formally described. It differs from the well-known panduriform variety of T. binalis by its mode of colony formation, smaller size, absence of a central constriction, and arrangement of valve spines. Since Ehrenbergs original drawing of Fragilaria (?) binalis cannot be matched with archive material, a neotype slide is designated.

A NEW FOSSIL SPECIES OF TETRACYCLUS (BACILLARIOPHYCEAE) FROM THE MIOCENE DEPOSIT OF TUNKA RIDGE, LAKE BAIKAL, SIBERIA, RUSSIA

Tetracyclus tscheremissinovae sp. nov., a new fossil Miocene diatom from Tunka Ridge, Lake Baikal, Siberia, is described. Comparison is made with similar extinct species and the palaeo-biogeographic implications of their distribution are discussed. A preliminary note on the holdings of the Baikal Museum is included.

VALIDATION OF DISCOSTELLA STELLIGERA VAR. MICROROBUSTA FLOWER VAR. NOV., A NEW NAME FOR CYCLOTELLA STELLIGERA VAR. MICROROBUSTA FLOWER

Regine Jahn and Karen Serieyssol kindly pointed out that two names were published for one new nomenclatural type in the same publication (see Flower 2005). This makes both names invalid (Greuter et al. 2000, Art. 34.2). Flower (2005) had described the new variety Cyclotella stelligera var. microrobusta from the Falkland Islands. At the manuscript proof stage, however, another publication appeared in which the stelligeroid Cyclotella taxa were transferred to a new genus, Discostella (see Houk & Klee 2004). A note to this effect and an intended new combination was inadvertently added to the proofs of Flower (2005).