Although an Irish Red Data Book species, it appears as though it may be widespread and locally abundant in Essex. It is difficult to tell whether its a new arrival that is increasing, possibly because it can now tolerate the current levels of much cleaner, recycled sewage water in our rivers and canals, or has not been recorded before, because nobody has looked for it along the centre of our canals and rivers. Our material all appeared, until recently, to conform to the var. mucronata with two-celled datyls, the apical cells being minute and onion shaped. The form that is claimed to be increasing elsewhere in Britain is predominantly the var. gracillima, a more slender, more umbellate plant, with tapering 2 to 3-celled dactyls, that has been found in Cambs. and Norfolk. The plants found in the R. Stort in December however, were developing narrow, needle-like terminal cells. Thus it seems that the shape of the terminal cell may be determined by the environment of the plant, and more recent gatherings in the county together with culturing experiments suggest that the `gracillima’ form is just an overwintering ecomorph. The larger summer form with axes up to 1mm in diameter can easily be mistaken for N. opaca or N. flexilis unless looked at under a microscope when the tiny apical dactyl can be observed. In the autumn side branches suddenly switch to the gracillima morphology and axis diameters  reduce down to 0.2mm, well within the range of N. tenuissima. Then in the spring side shoots of the larger morph begin to appear. Thus it seems likely that the so called var. gracillima and var. mucronata are illegitimate as they are not genetically distinct but are merely seasonal ecomorphs.

Hylands Park, Writtle, abundant in the centre of the long pond just south of Home Farm, under blanket of Lemna minuta, dense mats with main axes up to 10cm x 1.0mm, older parts blackish green, young tips translucent bright green, branches mostly twice forked, with two or three two-celled dactyls. Penultimate dactyl cells bluntly rounded, with terminal cell forming a mucro about x0.25 of the diameter of the former, very narrow and cylindrical, tapering to a finepoint, just visible to the naked eye. 17 June 2001. Peter & Pamela Wilson and Kenneth J Adams. Material kept indoors in a dish produced new delicate pale green fertile shoots by mid-July, with richly branched nests of oogonia/ antheridia bearing branches, the former developing first. This materialseemed to be of a similar phenotype to that found in the River Stort. Most of the dactyl apices being terminated by a tiny pointed cell as in (a), with a few exhibiting the other forms shown in the top row of Fig.1. Kept in a glass container indoors, however, by mid October 2002 these plants had became very fine and richly branched with the main axes no more than 2cm x 0.2mm and with most of the dactyl apices taking on the gradually tapered 2-3 celled-dactyl morphology characteristic of the var. gracillima [see bottom row Fig.1]. At the same time they also developed copious male and female gametangia. Material collected from the wild from Bourne Pond, Colchester in October 2002 was also fruiting and had exactly the same morphology. It would thus seem that the two supposed varieties of N. mucronata are one and the same genetically, and that they are simply ecomorphs of the same taxon. Responding, presumably, to the change in daylength by switching from the `mucronata' to the `gracillima' morphology as the days shorten in the autumn.

Only a single old record of this very rare Red Data Book species for Essex. It closely resembles the var. gracillima of Nitella mucronata, with its tapering 3-celled dactyls, but it is a smaller, more delicate plant with axes less than 0.5mm diameter, and has a yellowish to brownish-green, as opposed to dark green colour. Until a confirmatory specimen is located it is probably best to regard this record as doubtful as it could have been a small form of N. mucronata.