Le. Watson et al., GENETIC-VARIATION WITHIN AND AMONG POPULATIONS OF THE MARSHALLIA-GRAMINIFOLIA COMPLEX (ASTERACEAE), Biochemical systematics and ecology, 22(6), 1994, pp. 577-582
The Marshallia graminifolia complex has been variously treated as two
distinct species (M. graminifolia and M. tenuifolia), and as two subsp
ecies under M. graminifolia. Both are diploid and occupy the same bog-
like habitats along the Gulf and Atlantic coastal plains of the southe
astern United States. Enzyme electrophoresis was used to test various
hypotheses of speciational modes and mechanisms in the Graminifolia Co
mplex, including a progenitor-derivative relationship and gradual geog
raphic isolation. Nine enzymes encoded by 16 loci were resolved, 13 of
which were fixed for the same allele in all populations examined. Lev
els of heterozygosity were low. The mean genetic identity between the
two taxa was high (l=0.99). There was no evidence for a progenitor-der
ivative relationship, and no pattern of geographic partitioning of gen
etic variation among populations. Morphological variation between the
two taxa probably results from either simple polymorphism, phenotypic
plasticity, and/or clinal variation. Because other congeners of Marsha
llia share similarly low levels of genetic variation, we believe that
its species may have arisen from genetically depauperate ancestors.