Rayless Mock Goldenrod
Solidago discoidea (Ell.) Torr. & A. Gray has been treated as the only species in the genus Brintonia E.L. Greene as B. discoidea (Ell.) E.L. Greene. Unpublished polygenomic DNA research by Beck et al. (in prep.) found the species to be nested within S. subg. Solidago and Semple and Beck (2021) placed it in S. sect. Brintonia (Greene) Semple & Beck between S. sect. Squarrosae Semple & Beck and S. sect. Thysiflorae. Rayless Mock Goldenrods are herbaceous perennials found on sandy soils, rich, sometimes swampy woods on the coastal plain in Alabama, Northern Florida, Southwestern Georgia, Louisiana and Mississippi. Heads lack ray florets and have whitish disc florets tinted with purplish red. The pappus bristles are also usually distinctively purplish red. Flowering from August to October.
Brintonia and Chrysoma were reported to form a clade that is the sister genus to Solidago (Schilling et al. 2008) based on ITS and ETS gene sequences. The unpublished polygenomic study by Semple et al. and Beck (in review) involved sequence data from 893 nuclear genes and definitively placed the S. discoidea within S. subg. Solidago.
The species is diploid (2n=18). Semple and Cook (2022) published cytogeography maps for S. discoidea and related species.