AN EXPERIMENTAL APPROACH TO THE SYSTEMATICS OF THE MONOECIOUS-CONJOINED MEMBERS OF THE GENUS CHARA,SERIES GYMNOBASALIA

Most monoecious-conjoined members of the series Gymnobasalia, genus Chora, bear either tetrascutate or octoscutate antheridia. A determination of the extent to which various populations of these two morphologically distinct entities are reproductively isolated was the primary objective of the present study. Experimental crosses were attempted between emasculated sprigs and nonemasculated plants serving as sperm sources. All evidence suggests that tetra- and octoscutate populations are reproductively isolated throughout their respective ranges even to the extent of producing black oospores. Crosses were also attempted between geographically isolated tetrascutate, and again octoscutate, populations. All were uniformly successful to the extent that black oospores resulted; but when such oospores were germinated many of the resulting progeny were found to be either nonviable or dwarfed, and frequently self-sterile as well. This was particularly true where parental clones differed with respect to geographical origin, chromosome number, or external morphological features.