Vaucheria litorea is a species of yellow-green algae (Xanthophyceae). It grows in a filamentous fashion (forming long tubular cells connected end to end). V. litorea is a common intertidal species of coastal brackish waters and salt marshes of the Northern Atlantic, along the coasts of Europe, North America and New Zealand. It is also found in the Eastern Pacific coasts of Washington state. It is found to be able to tolerate a large range of salinities, making it euryhaline.
Taxonomy and nomenclature The species belong to Vaucheria were initially documented within the genus Conferva, at that time consisting of 21 species, when reported by Linnaeus in 1753. Vaucheria litorea have been categorized under Vaucheriaceae. Various historical classifications, found in older literature, situated Vaucheria among water molds and siphonous green algae. The species-level classification of Vaucheria has undergone considerable changes over the past century, involving the assignment of species to subgeneric sections and subsections. Presently, the genus Vaucheria is assigned to section Piloboloideae. The recent taxonomy of the genus relies on a morphological species concept, wherein species are characterized based on morphology, particularly the shape, size, and arrangement of antheridia and oogonia. Identifying closely related species poses challenges due to overlapping characteristics.
Description V. litorea characterized by siphons with apical growth. The antheridia are cylindrical-acuminate, terminal on siphons, 400–650 μm long, and distributed in frequent sympodial clusters. The dark green, filamentous dioecious algae forms loose interwoven bundles or dense sods, attached to the substrate by branched rhizoids. Filaments are coenocytic, 70–95 μm thick, dichotomously branched, and lack transverse cell membranes. Reproduction is vegetative (fragmentation), asexual (large multinucleate synzoospores), and sexual (fertilization of a non-motile ovule by a motile multiflagellate antherozoid). Like most algae, V. litorea obtains its energy through photosynthesis taking place in chloroplasts. V. litorea belongs to the Stramenopiles, a group currently housing red algal secondary-derived plastids. The chloroplasts of V. litorea are yellow-green, disc-shaped, small, and lack pyrenoids. Also they contain the photosynthetic pigments Chlorophyll a, Chlorophyll c, β-Carotene, and the carotenoid diadinoxanthin.
Plastid genome of V. litorea The V. litorea plastid genome lacks the complete set of components for any of the four multi-subunit complexes of the photosynthetic electron transport chain (including photosystems I (PSI) and II (PSII), cytochrome b6/f complex, and ATP synthase) and the reductive pentose phosphate pathway (RPPP or Calvin–Benson cycle). Essential genes in the thylakoid-localized electron transport chain, such as those encoding the PSI and PSII light-harvesting complex pigment/proteins, the PSII Mn-stabilizing protein, and the redox-regulated γ-subunit of ATP synthase, are notably absent. The plastid-encoded enzyme for RPPP is limited to the carboxylating enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). Unlike plants and green algae, both large and small subunits of RuBisCO are plastid-encoded in V. litorea.
Life history The evolutionary history of Vaucheria indicates that the ancestral form produced antheridia and oogonia as separate structures, possibly adjacent. The presence of a gametophore bearing both an antheridium and an oogonium is considered a derived character state that evolved once in the ancestral Vaucheria. Additionally, the ancestral Vaucheria is inferred to have produced a single terminal pore on the antheridium, with multiple pores evolving independently on two occasions. The dioecious condition of Piloboloideae is suggested to be a derived state, and the presence of a gametophore distinguishes a monophyletic clade (sections Vaucheria, Corniculatae).
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