Stoneworts and Their Habitats

Stoneworts, also known as charophytes are a family of algae
They live in a variety of wetland and freshwater habitats
Examples of habitats include disused aggregate sites, fenland ditches, bog pools, lakes, ponds, highland lochs and cattle tracks
Stoneworts are submerged species that generally prefer water depths between one and ten meters
They derive their name from the stony external texture acquired from encrustation, mainly with calcium carbonate
Earliest fossil records of stoneworts date back 460 million years
Recent DNA evidence has established stoneworts as precursors of all land plants
There are over 400 species globally
The UK supports approximately 30 species
Since the mid-twentieth century, the range of stoneworts has decreased significantly and the number of sites with extant populations has declined by over 60%, mainly due to habitat loss and pollution of both surface and groundwaters
Seventeen species are listed as Threatened or Endangered in the Red Data Book of British Stoneworts, while 11 species are currently listed as priority species on the UK Biodiversity Action Plan
There are five genera of stoneworts in the UK
- Chara: base-rich alkaline waters; species are often calcium-encrusted.
- Lamprothamnium: coastal lagoons.
- Nitella: less alkaline, softer waters (pH 6.5 - 7.5), lacking encrustation, and stem without cortex.
- Nitellopsis: mesotrophic lakes, lacking encrustation, and stem without cortex.
- Tolypella: calcareous ditches and canals.

Stoneworts do not have true leaves or roots
They have branchlets arranged in whorls around the stem, and possess fine rhizoids that anchor the plant into the sediment
Stoneworts have very large cells (up to 20 cm in length), with each branchlet, rhizoid wall and internode being one cell thick
While nutrient uptake can be through the rhizoids, gaseous exchange and most nutrient uptake are by direct transport from the water through the outer cells of the branchlets and stems.
Protonema: juvenile form of the stonewort that emerges from the oospore at germination, and gives rise to a new charophyte plant.
Rhizoid: colorless hair-like filament growing from the plant base into the substrate, with the dual function of absorption and anchorage.
Spine-cells: single-celled processes growing out from the node cells of the stem cortex in some Chara species.
Stipulode: a single or double ring of single-celled processes growing out from the base of the branchlet whorls.

Desmids are green algae
They are the earliest-evolved plants
Desmids share the same photosynthetic pigments as plants
They also build cell walls made of cellulose and store starch and chlorophyll inside double membrane-bound chloroplasts
Desmids are dual life forms
Most cells have two pronounced lobes spanned by an isthmus
They are named for "desmos," Greek for "bond"
Inside the bridge is the nucleus, and in each lobe is a single large chloroplast
A few species are colonial, occurring in chains instead of pairs
Desmids are creatures of freshwater – like peat bogs or ponds poor in minerals
Desmids are encased in slime
They secrete mucilaginous sheaths through pores in their walls
These gooey coatings host unusual and possibly symbiotic bacteria
Reproduction can be vegetative, by the production of propagules known as bulbils
Bulbils are formed at rhizoid-bearing joints
Bulbils can persist in the substrate and germinate when conditions improve

Stoneworts are highly sensitive to water quality
They are particularly sensitive to freshwater pollutants commonly associated with agricultural run-off and urbanisation
They are particularly sensitive to heavy metals such as copper, and to the effects of competition induced by dissolved nitrates and phosphates

Recent research shows that there is differential tolerance to water quality within and between stonewort species.
Based on a 'presence or absence' study of 123 water bodies at 49 important historical stonewort sites, the following approximate concentrations were shown to reduce the probability of stonewort establishment and persistence (Lambert 2007):
- Nitrogen in the form of nitrate at concentrations above 0.5 mgl-1 in open water.
- Phosphorus as inorganic phosphate at concentrations above 20 µgl-1 in open water.
- Copper at concentrations above 50 µgl-1 in the sediment pore water or 100 µgl-1 in open water.
The probability of stoneworts occupying a site is dependent on maximum concentrations of cobalt, manganese and silicate as well as minimum concentrations of calcium, chloride, magnesium, sodium and sulphate.
Salinity was also investigated, with growth and photosynthetic function being affected by changes in salinity.
Saline ingress as a result of managed retreat and rising sea levels may therefore be another limiting factor in stonewort survival.

Stoneworts are often the earliest colonisers of newly formed water bodies
They perform a number of important roles in aquatic ecosystems including:
- Enhancing water clarity by reducing flow rates and hence aiding sediment deposition
- Forming dense mats and hence aiding sediment stabilisation via rhizoid linkages
- Providing habitat for both anaerobic and aerobic microbes.
- Providing daytime shelter for phytoplankton-grazing zooplankton.