SKALSKY, J.L.; Texas A&M University: Floret morphlogical analysis of a putative Silphium (Asteraceae) hybrid population

Silphium albiflorum Gray (Asteraceae), an endemic to the central part of Texas, is considered to be derived from S. laciniatum L., also known as the compass plant. S. laciniatum is found from Texas to Minnesota and the ranges of the two species are sympatric. Synthetic crosses of many Silphium species have not been documented in nature. Many combinations of artificial hybrids have been shown to produce fertile progeny. Morphological analysis was conducted on the florets of heads from S. laciniatum and S. albiflorum and of a putative hybrid found in Kerrville, Texas. Three ray florets and three disk florets per head were sampled per head and three heads per population were sampled. At least 3 populations per species were included in this analysis, plus the single hybrid population. Florets were dissected with a dissecting microscope and photographed using a digital camera. Images of the florets included a small ruler to establish gauge in the image. The images were then measured using Image J and the data recorded. Early analysis indicates the plants in the Kerrville population are intermediate between S. albiflorum and S. laciniatum for the characters measured. The data support the hypothesis that the Kerrville plants are of hybrid origin. However, the possibility that they warrant recognition as a distinct taxon cannot be eliminated at this point. Further analysis of the Kerrville population is needed to determine if is a stable self-reproducing population. In addition, the use of molecular genetic markers will help to determine its origin.