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Taxonomic review of Chrysogonum (Asteraceae: Heliantheae)

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Abstract

Three allopatric varieties are recognized within Chrysogonum virginianum: the northern var. virginianum, with non-stoloniferous plants and mostly leafy aerial stems; the southern (Gulf coastal plain) var. australe, with flagellate stolons and only leafless aerial stems; and the geographically intermediate var. brevistolon, var. nov., with stolons of intermediate length and mostly leafy aerial stems. These three taxa are separated by other minor and overlapping differences. Intermediates apparently occur, but uncommonly, between var. virginianum and var. brevistolon. Variety australe is more strongly separated in geographic range and more distinct in morphology.

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... australe is the shortest, has prominent, long stolons, leafless flowering stems, and occurs in the most southern and western part of the range; var. brevistolon is of intermediate plant height, has stolons of medium length, has both leafy and leafless flowering stems, and occurs in the middle portion of the generic range (Nesom, 2001;Stuessy, 1973Stuessy, , 1977. The relationships and generic limits of Chrysogonum have been a source of controversy, as has the circumscription of taxa within the genus (Gray, 1882;Nesom, 2001;Stuessy, 1973Stuessy, , 1977. ...
... brevistolon is of intermediate plant height, has stolons of medium length, has both leafy and leafless flowering stems, and occurs in the middle portion of the generic range (Nesom, 2001;Stuessy, 1973Stuessy, , 1977. The relationships and generic limits of Chrysogonum have been a source of controversy, as has the circumscription of taxa within the genus (Gray, 1882;Nesom, 2001;Stuessy, 1973Stuessy, , 1977. An alternative taxonomy of the genus was proposed (Weakley, 2015); it recognized the ''australe'' entity at specific rank, presumably because of its allopatry and distinct morphology, in contrast to previous categorization that overlooked that fact (Nesom, 2001). ...
... The relationships and generic limits of Chrysogonum have been a source of controversy, as has the circumscription of taxa within the genus (Gray, 1882;Nesom, 2001;Stuessy, 1973Stuessy, , 1977. An alternative taxonomy of the genus was proposed (Weakley, 2015); it recognized the ''australe'' entity at specific rank, presumably because of its allopatry and distinct morphology, in contrast to previous categorization that overlooked that fact (Nesom, 2001). Issues with subtribal relationships were resolved with molecular phylogenetic data, starting with the studies based on enzymatic restriction of the chloroplast genome that explored the phylogenetic position of Chrysogonum in the Heliantheae tribe (Panero and Jansen, 1997;Panero et al., 1999). ...
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The genus Chrysogonum is native to the eastern United States. Three entities have been recognized—either as three varieties of Chrysogonum virginianum or as two species, one of them with two varieties. The current study suggests that a fourth entity should be recognized. Several forms of the complex are in commercial trade as ornamentals. As very limited molecular information on Chrysogonum is available, we developed a set of genic simple sequence repeat markers (eSSRs) from de novo transcriptome sequencing. We tested a set of 17 eSSRs on a collection of C. virginianum genomic DNA samples from the three botanical varieties, and a new putative type observed in Tennessee, dubbed ‘‘Ocoee-type’’ for its geographic origin. The polymerase chain reaction and capillary electrophoresis analyses with downstream population genetics tools verified the usefulness of the eSSRs. By applying this approach, we showed recognizable variation within Chrysogonum , although it did not correspond exactly to previous infraspecific classifications. Finally, as demonstrated for the commercial cultivar Pierre included in the study, the eSSRs can be used for enhancing the future breeding or hybridization efforts of this ornamental plant.
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