A Study of Trillium cuneatum and T. luteum

A systematic study was made of two taxa of the genus Trillium subgenus Phyllantherum. Morphological, biochemical, ecological, and distributional data were analyzed in order to reevaluate past taxonomic treatments of Trillium cuneatum and T. luteum.

Morphological studies revealed the similarities of the two taxa. It was noted that T. cuneatum exhibited great plasticity with respect to morphology, whereas T. luteum showed more homogenous features. This same relationship was noted with the flavonoids of the two taxa with T. cuneatum showing more variability than T. luteum. The chemistry of the two taxa was unique in that quercetin and kaempferol compounds identified portrayed significant glycoside diversity. A survey of past literature dealing with similar phenolic compounds resulted in an elucidation of the color variation seen within allopatric populations of T. cuneatum and led to a belief that T. luteum originally evolved from T. cuneatum as a homozygous recessive form which was favored due to more efficient sexual reproduction accompanying apomictic reproduction.

Scanning electron micrographs revealed different types of pollen grains which appeared to have taxonomic significance. The abaxial surfaces of the bracts apparently were identical. Photomicrographs were useful also in revealing spiders as possible pollinating agents within the genus. Predator--prey relationships and cryptic coloring are discussed as possible factors affecting reproductive success of the plants.

Recent taxonomic treatments were reviewed and possible taxonomic considerations were considered. Based on the results of this study and past work of other botanists, it was concluded that the two taxa should be recognized as distinct species in keeping with traditional treatments. It is believed that the two taxa represent a good case of directional selection resulting in divergent evolution. Whether this divergence will result in more speciation in the future or whether the two taxa will merge into a single unit via introgressive hybridization, is a stimulating academic consideration.