ESSEX BOTANY AND MYCOLOGY GROUPS |
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15a Nitella flexilis (L.) Agardh & Nitella opaca s.s. The former seems to be the most widespread Nitella in the Essex. The complex has monoecious and dioecious forms, which are supposed to be slightly different morphologically. The dioecious form is said to be smaller overall with denser heads, to be a darker, brownish-green, to have mucronate as opposed to tapering dactyl apices, a larger antheridum 650-775 μm (as opposed to 500-625μm) but a smaller oospore at 375-425μm as opposed to 500-575μm for flexilis (Groves & Bullock-Webster, 1920). In recent years the monoecious form seems to have been encountered most often in the county. As it tends to over-winter, producing antheridia in the spring, and oogonia in the summer (Allen, 1950), some of the Essex records of the dioecious form may be in error. The dioecious form is nowadays once again regarded as a separate species, N. opaca, but the type specimen has been shown to be monoecious, leaving us without a legitimate name. Moore, 1986 having found difficulty in being sure of the oecy of numerous, either sterile or apparent single sex specimens, suggested that all records, of, for the time being, an aggregate N. flexilis sensu lato, should note the presence/absence of antheridia/oogonia and the shape of the dactyl apices. No doubt, in years to come, a simple DNA test will become available to sort out the two forms, and it will become easier to correlate any morphological characters. |
Unless material can be collected in April/May, the chances of separating N. flexilis and N. opaca are thus pretty slim. Although the differences between the two taxa were summarised in Essex Naturalist (New Series) 14: p.135, due to the mismatch in automatic computer setting in those days, a female ostrich would have been proud of the oospores from either species, and a more plausible version is given here. Since the type specimen of `opaca' has been shown to be monoecious, `opaca' as a name is now illegitimate and we are left without one. Thus all we can do is record the dioecious plants as `N. opaca' until someone sorts out the nomenclature. Unfortunately, as illustrated above, N. flexilis usually produces its antheridia precociously during the winter and spring, and its oospores in the summer, by which time the antheridia have fallen off or been eaten. Thus unless it is collected around April/May time, and a lot of material looked at, its monoecy may not be apparent. The antheridia and oogonia of both taxa develop in the crotch between the paired dactyls (ultimate branches of the branchlets). In N. flexilis, at some stage, an antheridium should be found with 2-3 oogonia in the same crotch. In N. opaca the oogonia are supposed to be produced earlier than in N. flexilis and to be present as one or occasionally two per crotch. Its mainly on the size of the antheridia, however, that separations of the two taxa are made. The oospores are also supposed not to overlap in size - care must be exercised here however, in not confusing the larger oogonia with the ripe oospores that are shed from the spiral sheath of oogonial cells, and have a spiral flange derived from the radial walls of the five sheath cells. It would seem that our best policy is to culture would-be collections of N. opaca / N. flexilis over the winter and on into the summer. If only oogonia or only antheridia appear over this period then we must have N. opaca. Antheridia appearing first followed by oogonia on the same plants in the spring obviously indicate N. flexilis. Other supposed differences such as mucronate dactyl apices (N. opaca), size/colour of the plants and density of branching, may be loosely correlated, but seem to be inconsistent. From now on every record to be reliable will have to be annotated with detailed evidence for its identification. I am still not entirely convinced that these two are not monoecious and dioecious forms of the same taxon as proposed by Wood in Wood & Imahori 1965. Only confirmation of a consistent difference in the sizes of the gametangia and the timing of their develpment can clinch the issue. |
Groves & Bullock-Webster (1920) provide the following diagnostics: | ||
N. opaca | N. flexilis | |
oecy | dioecious | monoecious |
antheridia | 650-775μm diameter | 500-625μm diameter |
oogonia | 1-2 per crotch and 650-700μm long x 500-565μm wide | 2-3 per crotch and 625-900μm long x 550-750μm wide |
oospores | 375-425μm long x 350-400μm wide x 250μm thick (oval in section) | 500-575μm long x 425-500μm wide x375 thick (oval in section) |
Nitella opaca/flexilis
(indeterminate) [ scroll down for Nitella flexilis s.s.]
TQ(51) 49 |
424,975 |
18 |
Epping Forest, Baldwins Pond, 12 April 1959. Coll: Bernard T. Ward, det:? by Eric Saunders. |
Essex Naturalist. 30. p.284. 1960. |
418,984 |
18 |
Epping Forest, V2 Rocket Crater Pond, Wake Valley, Sept. 1978. Coll: & det: K.J. Adams. Confirmed J.A. Moore. |
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423,978 |
18 |
Epping Forest, material of this complex reported in quantity in the Lost Pond, on the south side, following recent excavation of the delta area. No further details. August 1999. Amanda Samuels |
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420,987 |
18 |
Wake Valley Pond, scattered around margins, mainly small fragments, 30 Sept. 1989. Coll: & det: Tim Pyner. |
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429,981 |
18 |
Goldings Hill Upper pond, abundant in shallows, large lax form, in areas of open water cleared by dredging in 1985. No sign of reproductive structures, but apices very pointed. 20 Aug. 1986. Coll: & det: K.J.Adams. |
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ditto |
still present on north side, still sterile. 28 Sept. 1986 K.J.Adams. |
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ditto |
still present on north side, with a new form of N. translucens, 25 Sept. 1989. K.J.Adams. |
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415,967 |
18 |
Strawberry Hill Pond, Epping Forest, abundant in the shallows on the north-east shore, sterile, 27 August 1989. Coll: & det: K.J.Adams. |
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TL(52) 43 |
42 ,36? |
19 |
Pond between Langley and Chrishall. As Chara flexilis c.1840. George S. Gibson |
Flora of Essex p.405. 1862. |
464,343 |
19 |
Clavering, new fishing lake. 19 August 1999. Shirley & Charles Watson. |
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TL(52)51 |
536,128 |
19 |
Matching, new farm reservoir at Parvilles, with Potamogeton crispus,P. trichodes and Myriophyllum spicatum. Tatty, end of season material,rather dark and with short distinctly mucronate dactyls. Infertile. Possibly N.opaca. 21 August 1999. Shirley & Charles Watson. |
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TL(52)52 |
558,255 |
19 |
Takeley, choking recently excavated linear pond on the west side of East End Wood,growing with Chara globularis var. gobularis. April 2002. Shirley & Charles Watson |
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TQ(51)69 |
61 ,90? |
18 |
Spring near Childerditch, July 1860. Coll: W.Hind, det: Charles C.Babington (as Chara flexilis). |
Trinity College Dublin. Herbarium (TCD), and Flora of Essex. p.405. 1862. |
TL(52) 70 and TL(52)80 |
??????? |
18/19 |
Chelmer and Blackwater Canal, between Maldon and Chelmsford, 8 August 1891. Dr. Pearl. |
Essex Naturalist. 5. p.252. 1891. |
TL(52) 71 |
748,125 |
19 |
Boreham, old gravel pit nr. Brent Hall, scarce in deep water amongst plentiful Chara vulgaris and Potamogeton berchtoldii, sterile. 14 July 1990. Tim Pyner |
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TL(52)90 |
973,016 |
18 |
.Plentiful, deep water, main pond, Asheldham gravel pits, apices acute, annular incrustations present, sterile. ll Oct 1987 Coll: & det: Tim Pyner. |
Pickled material in Southend CentralMuseum Herbarium (STD). |
TM(62)02 |
00 ,23 |
19 |
Bourne Mill Pond, Colchester, extensive stands with filamentous algae., Nov 1997. P. Williams. det> N E Stuart. |
probably the N. opaca recorder later(KJA). |
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Nitella flexilis s.s.
TQ(51) 38 |
?????? |
18 |
Epping Forest, pool near Snaresbrook, a rather small form growing in dense masses. 13 May 1882. H. Groves. |
Four specimens in Natural. History Museum Herbarium (BM) Atlas Specimen No.1597. |
TQ(51) 39 |
39 ,92 |
18 |
Epping Forest,`in the Forest', Prospect House, Woodford Wells, c.1840. Edward Forster. Conf. J.Groves. |
Natural History Museum Herbarium (BM). Atlas Specimen No. 1598. |
TQ(51)49/ TL(52)40 |
??? |
18/19 |
Epping (upper) Forest, E. de Crespigny. |
A New Lonodon Flora. 1877. p.80. |
TQ(51) 49 |
??????? |
18 |
Pond near Woodford, 16 June 1877. Henry Groves. (as Chara flexilis) |
Botanical Exchange Club Report. 1. p.11. 1877-78. Also three specimens Natural History Museum Herbarium (BM). Atlas Specimen No. 1599. |
418,984 |
18 |
Epping Forest, Little Wake Valley Pond East, 9 May 1894, Coll: W.P.Hiern, conf: Nicholas F Stewart |
Exeter Herbarium (RAMM). |
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415,967 |
18 |
Epping Forest, Earl's Path Pond, very abundant in dense mats with Utricularia neglecta and Eleogiton fluitans, pond cleaned out in 1976, bare gravel bottom, (clearly monoecious). 29 July 1981. Coll: & det: K.J.Adams. |
Specimen Spirit No. L252. |
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ditto |
still there March 1984. K.J. Adams. |
Pickled material deposited in NaturalHistory Museum Herbarium (BM). |
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ditto |
still there 5 May 1986, antheridia only, grown on indoors and both antheridia and oogonia present by 26 May. K.J.Adams. |
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ditto |
still present, sterile. 6 March 1988. K.J.Adams. |
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418,984 |
18 |
Little Wake Valley Pond West, antheridia and oogonia present, 8 May1988. Coll: & det: K.J.Adams et al. |
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418,966 |
18 |
Staples Road New Pond, retrieved by grapnel from the centre, clearlymonoecious with immature antheridia and oogonia. 20 April 1997. Coll: & det: K.J.Adams. |
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429,980 |
18 |
Epping Forest, Goldings Hill Upper Pond, small patches on south margin, numerous mature oospores, a few moribund antheridia, clearly monoecious. 6 July 2004. K. J. Adams. |
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422,982 |
18 |
Epping Forest, Oak Pond, High Beach, in quantity in the shallows, with Utricularia australis (in flower); showing signs of regrowth presumably after the recent rains following the drought. Some apical segments with mature oospores, others with combined clusters of young oogonia and antherida. Clearly monoecious, but exceptionally late for immature antheridia. Water so shallow that must have dried out during the drought, recent flooding therefore having encouraged regrowth and anomalously late fructification.30 July 2004. Kenneth J Adams et FSC students. Still present in quantity 22 July 2011, but no sign of oogonia or antheridia. Kenneth J Adams et FSC students. |
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TL(52)40 | 43343,99730 G | 18 | Bomb Crater Pond, Long Running, with Potamogeton natans and Utricularia neglecta. Clearly monoecious with immature groups of two nucules and one globule.17 May 2009. K.J.Adams. | |
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44770,01141 G |
19 |
Bell Common Pond, plentiful, growing attached to Lagarosiphon major, clearly monoecious with precocious antheridia and small developing oogonia.29 April 2003. Kenneth J Adams.[by the 24 May the oogonia were mature, and arranged in pairs, but most of the empty antheridia had either dropped off or were being/had been eaten by Physia fontinalis snails. These observations highlight the difficulty in distinguishing the dioecious N. opaca]. In a remarkable coincidence, I quote from Groves and Bullock-Webster 1920. "on specimens gathered on 29th April, the antheridia were numerous and many had attained their full size, while a few oogonia were to be found, and these so small as to be hardly visible, so that the plant appeared entirely male. On specimens gathered towards the end of June, the conditions were reversed, fully formed oogonia being numerous and antheridia few, so that the plant appeared female; at intermediate dates the plant was obviously monoecious" Although this quote applies to their var. fryeri, Guy Allen (1950) had the same problem with more normal N. flexilis at Hazelmere. |
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471,032 |
19 |
In the lake, Epping Lower Forest, clearly monoecious, 22 Sept. 1985. Coll: JohnBratton, det: K.J.Adams. |
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TL(52)81
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87890,14520 | 19 | Tiptree Heath, abundant in pond in south west corner of the heath, nucules and globules present 4 June 2009. Peter & Pam Wilson. Det: K JAdams. |