The Essex Naturalist
135
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 650-775mm (as opposed to 500-625mm) but a smaller oospore at 375-
425mm as opposed to 500-575mm 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 was formerly 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,
suggests that all records, of, for the time being, an aggregate N. flexilis sensu lata,
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.
TQ(51)49/ ?????? 18/19 Epping Forest, (as N. opaca), vague record, c.1850.
or Edward Forster.
TL(52)40 Natural History Museum Herbarium (BM). Atlas
Specimen No. 1780.TQ(51)38 ?????? 18
Epping Forest, pool near Snaresbrook, a rather small
form growing in dense masses. 13 May 1882. Four
specimens in Natural History Museum Herbarium
(BM). Atlas Specimen No.1597.
TQ(51)39 ?????? 18 Chingford, (as N. opaca), 3 May 1884. H.G.Slatpole.
Natural History Museum Herbarium (BM). Atlas
Specimen No. 1779.
39 ,92 18 Epping Forest, "in the Forest", Prospect House,
Woodford Wells, c. 1840. Edward Forster. Natural
History Museum Herbarium (BM). Atlas Specimen
No. 1598.
TQ(51)49 ??????? 18 Woodford, 16 June 1877. Henry Groves. Botanical
Exchange Club Report. 1. p.11. 1877-78. Also
three specimens Natural History Museum
Herbarium (BM). Atlas Specimen No. 1599.
424,975 18 Epping Forest, Baldwins Pond, 12 April 1959. Goll:
Bernard T. Ward, det:? by Eric Saunders. Essex
'Naturalist. 30. p.284. 1960.
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). July 1981. Coll: & det:
K.I.Adams.