Oheisia

Oheisia is a fictional genus of freshwater green algae created for the purpose of this encyclopedia-style entry.

Oheisia is a small genus of freshwater green algae in the family Oheisiaceae. The genus is monotypic, currently containing a single described species, Oheisia lumina. First collected from montane streams in the Western Ghats and formally described in 1987, Oheisia is noted for its simple, filamentous habit and its narrow geographic range.

Description: Oheisia lumina forms uniseriate, branching filaments composed of cylindrical cells about 12–16 micrometers long. Each cell contains a single cup-shaped chloroplast with a small pyrenoid. The filaments often form slimy biofilms on submerged stones, and the overall appearance is pale green to olive when in culture.

Habitat and distribution: It inhabits cool, clear, well-oxygenated streams at elevations roughly 900–1,800 meters, with neutral to mildly acidic pH. It is locally distributed in select montane habitats in parts of the Western Ghats and adjacent regions, and is rarely encountered outside its native range. Susceptible to pollution and sedimentation.

Life cycle and reproduction: Oheisia lumina reproduces primarily by fragmentation, enabling rapid colonization of available substrate. Sexual reproduction is infrequently observed in cultured material, where isogamous zygotes have been reported, followed by meiosis and formation of propagules that reseed the filaments.

Taxonomy and naming: The genus name Oheisia honors the late botanist Keiko Oheishi, in recognition of early work on freshwater algae in montane streams. The species epithet lumina refers to a faint luminescent mucus that some filaments emit under certain light conditions in culture.

Ecology and significance: Oheisia lumina is used in bioassessment studies as an indicator of clean-water habitats and is sometimes employed in introductory phycology teaching. Its restricted distribution and sensitivity to environmental changes make it of interest for studies on montane stream ecology and algal evolution within Chlorophyta.