New Charophyte (Stonewort) records
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;
antheridia
oogonia
oospores
Nitella opaca s.s.
TM(62)02 004,238 19
Colchester, Bourne Pond, fust recorded in October 2002, still present
June 2003 and material cultured to October 2003 (still no gametangia).
Peter and Pamela Wilson. Ken Adams (KJA) collected large quantities
from the pond in November 2002 but no sign of gametangia. However, on
12 May 2004, KJA collected material from several places along the road
bank and all of it had immature antheridia, even the young shoots had
minute green antheridia in the axils of the dactyls. The material collected
by Peter and Pam in October 2002 and cultured in a container in their
garden, also produced antheridia in May 2004.
This material is thus clearly dioecious, and the entire Bourne Pond population is probably male, and
therefore N. opaca s. s. As these antheridia were immature in May, [whereas those of N. flexilis would be
going over by this datej it may be that N. opaca antheridia mature much later than those of the former.
We need to see more material over several years and to find female clones of N. opaca. Unfortunately,
minute Limnaea, snails, the same size as the antheridia, devoured them all before they had a chance to
mature in KJA's cultures! The Wilson's had better luck and antheridia on their plants persisted until at
least 1 August in 2004.
Essex Naturalist (New Series) 21 (2004)
43