Phylum Chlorophyta, Family Order Ulotrichales, Family Ulotrichaceae.
Filaments slender, unbranched, no mucilage sheath. Cells 1-2 times longer than broad, 1 discoid chloroplast per cell, lying at the periphery of the cell wall but not extending all the way round it. Typical habitat is rapidly flowing shallow water, e.g. in the splash zone of a waterfall.
Hormidium is particularly resistant to low pH and high metal concentrations.
This is a typical view, the sample is from a culture. The disc-shaped chloroplast is wrapped around about half of the cell periphery. The cell wall is very distinct and well-defined.
Filaments are usually straight-sided, but sometimes the cells may become swollen and bulbous
|This kinked filament is quite typical: sometimes there is a disc of a clear material surrounding the 'knee', seen when the alga is growing in culture on a slide|