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Taxonomy in silica-scaled chrysophytes has gone through three morphological phases. From primary studies of the cell morphology in the 18th century, the focus was in the 20th century replaced by studies of the silica structures of the cell envelope. Now, in the latest decades the importance of DNA sequencing has been recognized, not only to support the taxonomic framework but also to obtain new understanding of taxonomic relations among particular taxa. In the first part of this review, we provide a historical overview of the developments in the taxonomy of scale-bearing chrysophytes. In the second part, we present a phylogenetic reconstruction of chrysophyte algae, updated by newly obtained SSU rDNA and rbcL sequences of several isolated Synura, Mallomonas and Chrysosphaerella species. We detected significant incongruence between the phylogenies obtained from the different datasets, with the SSU rDNA phylogram being the most congruent with the morphological data. Significant saturation of the first rbcL codon position could indicate the presence of positive selection in the rbcL dataset. Within the Synurales, the relationships revealed by the phylogenetic analyses highlight the artificial infragenetic classification of Mallomonas and Synura, and the occurrence of cryptic diversity within a number of traditionally defined species. Finally, three new combinations are proposed based on the phylogenetic analyses: Tessellaria lapponica, Synura asmundiae and S. bjoerkii. Silica-scaled chrysophytes belong to the class Synurophyceae and the family Paraphysomonadaceae in the class Chrysophyceae. Historically, their taxonomy has passed through several stages, and will here be discussed from morphological, light-microscopical, electron-microscopical, and molecular viewpoints. After the beginning in the 19th century with purely coarse-morphological concepts of cell construction, the scaly envelopes of these genera were discovered, and light microscope (LM) studies of the silica structures were initiated and came into focus for the taxonomy and identification. Later, electron microscopy (EM) opened up for new possibilities, and the ultrastructure of scales became the standard tool for taxonomy. Several genera were exclusively described and studied by EM.

The fluxes of CO 2 and oxygen during photosynthesis by cell suspensions of Tessellaria volvocina and Mallomonas papillosa were monitored mass spectrometrically. There was no rapid uptake of CO 2, only a slow drawdown to compensation concentrations of 26 lM for T. volvocina and 18 lM for M. papillosa, when O 2 evolution ceased, indicating a lack of active bicarbonate uptake by the cells. Darkening of the cells after a period of photosynthesis did not cause rapid release of CO 2, indicating the absence of an intracellular inorganic carbon pool. However, upon darkening a brief burst of CO 2 was observed similar to the post-illumination burst characteristic of C3 higher plants. Treatment of the cells of both species with the membrane-permeable carbonic anhydrase inhibitor ethoxyzolamide had no adverse effect on photosynthetic rate, but stimulated the dark CO 2 burst indicating the dark oxidation of a compound formed in the light. In the absence of any active accumulation of inorganic carbon photosynthesis in these species should be inhibited by O 2. This was investigated in four synurophyte species T. volvocina, M. papillosa, Synura petersenii, and Synura uvella: Photosynthetic O 2 evolution rates in all four algae, measured by O 2 electrode, were significantly higher (40-50%) in media at low O 2 (4%) than in airequilibrated (21% O 2) media, indicating an O 2 inhibition of photosynthesis (Warburg effect) and thus the occurrence of photorespiration in these species. © Springer Science+Business Media B.V. 2011.