Effect of Nutritional Conditions on Sexual Reproduction in Riccia

Abstract

Riccia duplex Lorbeer ex Miiller thallus branches elongate rapidly in the vegetative phase and much more slowly in the reproductive phase. Slow growth and sporophyte formation are brought about by low nutrient conditions, in particular low nitrate availability. In such conditions increasing daylength reduces the time for sporophyte formation. Two out of four clones of R. fluitans L. and one of two clones of R. rhenana Lorbeer ex Miiller formed archegonia when cultured on solutions providing low nutrient conditions. Antheridia were not formed on either of these two latter species under laboratory conditions. R. rhenana Lorbeer ex Miiller is not known to be fertile in nature. Miller (1941, 1954) gave extensive descriptions of four species of Riccia, R. fluitans L., R. rhenana Lorbeer ex Miiller, R. canaliculata Hoffm. and R. duplex Lorbeer ex Miller, which he treated as a species complex but separated clearly on the basis of chromosome number and fertility. Ricciafluitans (n = 8) and R. rhenana (n = 16) were only known sterile, while R. canaliculata (n = 8) and R. duplex (n = 16) were known to be fertile under natural conditions. More recent observations have made this relatively neat separation appear less convincing. After studies on artificially induced polyploidy of members of the R.fluitans group, Berrie (1964) concluded that R. rhenana is the diploid of R. fluitans and that R. duplex is the diploid of R. canaliculata (i.e. that the two infertile and the two fertile species form two separate polyploid series). Klingmiiller (1958) added to the R. fluitans group R. media, a new, though not widely accepted, European species (Bapna, 1961; Berrie, 1964). Bapna (1962) added an Indian species, R. abuensis, and Arnell (1963), a South African species, R. stricta, to the group. Meijer (1958) accepted the four member species of the group when considering European material, but returned to the R. fluitans sensu lato terminology when handling Indonesian material. He felt detailed studies of living material from many parts of its whole range would be needed for an understanding of the group. Riccia fluitans, sensu stricto, has until recently been regarded as always sterile. However, Paton (1973) described archegonia and sporophytes on both land and water forms from Britain; antheridia were not seen. Paton suggested that conditions at the site or in the local climate may suddenly have become favorable for the formation of sex organs, but did not suggest what conditions might have been important. 1 Thanks are due to Dr. D. Adamson, Dr. G. Berrie, Mr. J. Dickson, Dr. W. Klingmiiller, Mrs. E. Morris, Dr. S. Segal, Dr. Thai-thong, Mrs. C. Thomas, Dr. J. V~aia and Dr. E. Watson for collecting or supplying specimens. 2 School of Biological Sciences, Macquarie University, North Ryde, 2113. Australia. 0007-2745/79/037-046$1.25/0 This content downloaded from 207.46.13.176 on Mon, 20 Jun 2016 07:31:11 UTC All use subject to http://about.jstor.org/terms 38 THE BRYOLOGIST [Volume 82