The Essex Naturalist
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from the apex of which arise up to twelve unicellular filaments formed of up to
200 cells. Each cell giving rise to a worm-like, helically-twisted, biflagellate
antherozoid, an estimated 20-30,000 per antheridium.
The familiar Stonewort plant is normally haploid, the oospore undergoing
meiosis as it germinates, only one cell from the resulting tetrad giving rise to the
plant, the other three aborting. In Chara canescens found in northern Europe,
Britain and Ireland, however, the plant is diploid, always female and apogamous.
Elsewhere separate male and female haploids occur, so its well worth examining
any C. canescens plants for the presence of antheridia, which would be new to
the British Isles. Of the other British taxa, all the Nitellas and Tolypellas are
monoecious except for N. capillaris and N. flexilis, the latter having both
monoecious and dioecious forms, which are slightly different morphologically
and have in the past been regarded as separate species. Unfortunately, the
monoecious form frequently develops its antheridia first and its oogonia later on,
giving the false impression of being dioecious, so its probably as well they are
nowadays lumped in the same taxon. The name N. opaca, formerly applied to
the dioecious form, has in any case been shown to be illegitimate as the type
specimen is monoecious! At the specific level about half our Charas are
dioecious and half monoecious.
How and where to find Stoneworts
Stoneworts can occur in anything from a shallow temporary grassy pool in a
meadow to a large farm or water company reservoir. In warm shallow water, they
can grow at a phenomenal rate during the summer, and completely fill the water
column. On the other hand, they can also grow rapidly at low temperatures, and
can be grown-on to maturity successfully in a dish, providing the temperature is
kept low. Otherwise they become rapidly enveloped, and fatally overwhelmed,
by unicellular and filamentous green algae. They like high light intensities,
however, and cannot compete with higher plants. They often occur in
abundance in the otherwise bare shallows of a pond, where they are frequently
completely covered in a buff-brown covering of rotifers, diatoms and other algae.
Despite this fluffy-looking state, their overall string-of-umbrellas morphology
stands out to the initiated eye. When growing in dense tangled masses, their
characteristic form is obscured, and they may just be passed over as filamentous
blanket algae. A good place to find them is in a completely new pond the year
after it has been excavated, and before any higher plants have taken hold. The
other main habitat is less obvious, and most often overlooked, the centre of a
pond or lake, or the central channel of a river or canal. These locations can only
be profitably investigated using a long-haul grapnel and some patience, as they
may only be present in localised patches. Of their potential habitats in Essex,
three stand out as being important from the point of view of maintaining the
bulk of the populations. The shallows of livestock drinking ponds and lakes
provide a warm, high-light-intensity environment during the summer, but they