New Charophyte (Stonewort) records
KEN ADAMS
School of Health and Bio sciences, University of East London E15 4LZ
Charophytes
Records added to the data base for 2003.
Nitella flexilis sensu stricto
TL(52)40 447,011 19 Bell Common Pond, plentiful, growing attached to Lagarosiphon
major, clearly dioecious with precocious antheridia and small
developing oogonia. 29 April 2003. Ken 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.
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
Scries) 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, 'opaca7 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 monoccy 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 oogonia! 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
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Essex Naturalist (New Series) 21 (2004)