The floating liverworts of Essex
Riccia rhenana Lorbeer
A central European taxon, very close to R. fluitans, and believed to be its autodiploid. that occurs
occasionally in this country, either as a presumed introduction from the contents of an aquarium
tipped into a pond, or possibly sporadically on birds1 feet from the continent. The floating form
generally has a thallus wider than R. fluitans, typically 0.8 - 1.2mm wide, with very large air
chambers (0.5-1.0mm long) giving the surface an obvious reticulate appearance, and a translucent
margin, the whole strap-shaped thallus being proportionately thinner than in R. fluitans. When
stranded on mud, unlike R. fluitans it forms semi-rosettes to 1.5cm across with the thalli up to
2.5mm wide. Antheridia, archegonia and sporophytes appear never to have been recorded. Damsholt
suggests growing the thalli of doubtful plants on mud to see if they form rosettes.[ Both R. rhenana
and R. fluitans differ from R. canaliculata in the absence of a groove along the upper surface of the
thalli].
TQ(51 )39 398,945 18 Epping Forest, the Warren Pond opposite the Queen Elizabeth's
Hunting Lodge. Floating in the shallows, 1984. Kenneth J. Adams
(BBS Herbarium, National Museum of Wales, Cardiff, and
Bulletin Brit. Byol. Soc. 1985). [site subsequently dredged and not
seen since].
The author has drawn heavily on the following sources for the accounts of the above species.
References
ADAMS, K.J. (1974) Bryophytes. In Flora of Essex. S.T. Jermyn, pp.229-271. Essex Naturalists'Trust.
Colchester.
DAMSHOLT, K. & PAGH, A. (2002) Illustrated Flora of Nordic Liverworts and Homworts.-pp.837. Nordic
Bryological Society. Lund.
HILL, M.O., PRESTON, C. D. & SMITH, A.J.H. (1991) Atlas of the Bryophytes of Britain and Ireland
Vol.1. Liverworts, pp.351. Harley Books. Colchester.
PATON, J.A. (1999) The Liverwort Flora of the British Isles, pp.626. Harley Books. Colchester.
PETTIFER, AJ. (1968) A Bryophyte Flora of Essex. Essex Naturalist 32: 83-155.
SCHUSTER, R.M. (1992) The Hepaticae and Antherocetae of N. America East of the 100th Meridian. Vol:6
Marchantiales. pp.937. Field Museum of Natural History. Chicago.
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