BACK TO STONEWORTS

The Essex Records 1820 -2007.

Following the introductory paragraph to each taxon, the records are set out in columns. The first being the letter and alternative number (in brackets) code for the 100 x 100km square, followed by the 10 x 10km square number, arranged in conventional order from south to north, moving from west to east; the second column gives the 1 x 1km square or the 100 x 100m square Ordnance Survey grid reference if known; the third the vice county, and the final column the available details of the individual record. Approximate grid references for older records are suffixed by a (?)

Nitella mucronata (A.Braun) Miquel           MAP                        [ see old erroneous? record for N. gracilis below]

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.


TQ(52)39,88 394,887 18 Hollow Pond, Leyton Flats. Grapnel sample. 19 July 2017. K.J.Adams.  
  3937,8887 18 Hollow Pond, Leyton Flats. A few fragments in shallow bay. 19 July 2018. K.J.Adams.  

TQ(52) 49



Small plastic-lined pool by Epping Forest Conservation Centre, High Beach, 4 March 1995. Coll: & det: K.J.Adams.

  413,980 18 Growing with Elodea nuttallii in the teaching pond at the rear of the Conservation Centre, High Beach. 11 July 2009. K J Adams. Huge mats in the pond in July 2010, fruiting.K J Adams.  
  4848,98440 18 Lesser Wake Valley Pond West, a solid mass growing with Potamogeton natans, up against central western edge.  20 July 2012. K.J.Adams et EFC students.  
  4189,9840 18 Lesser Wake Valley Pond East, a few fragments south side among Crassula helmsii. 19 July 2018. K.J.Adams.  




R. Stort nr. Harlow Marsh, with Elodea nuttallii 1 August. 1998. Charles Watson.




R. Stort, Shearing Mill Lock, retrieved by grapnel from central channel, plant with long pointed, mucronate terminal cells and 2-celled dactyls, no onion shaped terminal cells. 29 December 1997. Charles Watson




R. Stort between Spellbrook Lock and Tednambury Lock, 10 February 1998. Charles Watson.




East side of R. Stort, Gt. Hallingbury, Sept. 1987. Coll: Shirley & Charles Watson, det: K.J. Adams.


49 ,19


All the way down the R. Stort Navigation from Bishop's Stortford to Twyford's Lock, in deep water with Chaetomorpha. 4 Oct. 1987. Coll: & det: K.J.Adams et LNHS/EFC


49 ,18


R. Stort, just north of Wallbury Dells, N. Essex. 22 Feb. 1992. Coll: & det: Jeremy Ison.


495,200 to495,192


R. Stort, all the way down stream between these limits, 22 June 1992. Coll: & det: Jeremy Ison.





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.


TL(52) 70



Detached material on weir, sterile, Chelmer & Blackwater Canal, nr. Cuton Lock, Springfield. 9 Feb. 1991. Coll: & det: Tim Pyner.




Boreham, in Chelmer-Blackwater canal, sterile, nr. Stonehams Lock. 7 August 1990. Tim Pyner

TQ(51)88 8769,8749 18 Southend, Prittlewell Priory Park, small round artificial pond. 26 January 2010. James Bishop.(Det: K J Adams). Still present,  with globules and nucules. 24 August 2012. Roger Payne. Det: Tim Pyner.  

TL(52) 80



Chelmer & Blackwater Navigation, just east of Hoe Mill bridge, Ulting, retrieved by grapnel from the central channel on  Vcl8-19 boundary, with Potamogeton trichodes. 12 Aug. 1990. Coll: & det: K.J.Adams et EFC.

  808,082 18/19 Chelmer & Blackwater Navigation, by Hoemill bridge. 14 January 2008. Colin Austin.  
TL(52)82 839,263 19 Coggeshall C.P., small woodland pond in Markshall Park, with both globules and nucules. 19 July 2014. Collected: Peter & Pam Wilson. Det: K.J.Adams. [form with small mucronate 'summer form' terminal cells.  
TM(62) 02 005,257 19 River Colne, Colchester, growing with Elodea nutallii and E. canadensis, c. 1/3 way across (grapnel). Material sterile and very stout (main axes 1mm), most ends eaten off, rapidly growing tips producing the delicate `gracillima' expression with the approach of autumn. Collected Peter Wilson. Det: K J.Adams. July 2006.  


004,259 19 R. Colne, Colchester. 13 January 2008. Colin Austin.  
TM(62) 13 140,300 19 Bradfield Junior. School, small school pond, in piles on bank having just been raked out. Plants with the large summer (0.5mm diam) filaments dying and new `gracillima' shoots being produced (KJA). 31 January 2006. Peter & Pam Wilson. Confirmed. K.J.Adams  


Nitella gracilis (Smith) Agardh

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.




Near Sudbury, on Essex side of Stour, as Chara gracilis, c.1850. Dr Ezekiel G.Varenne.

Flora of Essex p.406. 1862.