URBATSCH, LOWELL1*, PATRICIA COX2, and RICHARD RUTH1. 1Louisiana State University, Baton Rouge, LA; 2University of Tennessee, Knoxville, TN. - Is Rudbeckia heterophylla (Asteraceae, Heliantheae) a central Florida endemic of “ancient” hybrid origin?
Rudbeckia heterophylla, a species in the southeastern clade of
subgenus Macrocline, is restricted to Levy County Florida where it is
locally abundant. Although originally described as a distinct species,
it has been treated for the past 50 or more years as a variety of the
widespread, common R. laciniata based largely on their sharing
deeply lobed to pinnately compound cauline leaves. Spontaneous garden
hybrids between R. auriculata, a species restricted to Alabama
and the panhandle of Florida, and R. laciniata resemble R.
heterophylla in having simple basal and upper cauline leaves
–characters used to separate this taxon from other entities of R.
laciniata. ETS sequences of R. auriculata and R.
laciniata are complemented in the garden hybrid and clearly show
at least 12 polymorphic sites. ETS sequences for several individuals
of R. heterophylla from Levy County show a similar degree of
polymorphism indicating their possible hybrid nature. The
polymorphisms, however, are not the same as seen in the garden
samples. In order to determine more precisely the origin and nature of
R. heterophylla, ETS sequence variation is being explored
further in R. mohrii and R. nitida which are also
members to the southeastern Macrocline clade. The fact that R.
heterophylla is completely allopatric from its sister taxa
suggests that the probable hybridization event had taken place in the
distant past, and that geographic distributions for these taxa or
their ancestors differ dramatically from the present.
Key words: Asteraceae, DNA sequence data, ETS, Heliantheae, phylogeny, Rudbeckia