ABSTRACT Assessing the factors that may contribute to rarity in flowering plants is important in preserving biodiversity. One method of examining these factors is through comparisons of rare species to more common congeners. While these studies are fairly common, most focus on comparisons of intrinsic factors, such as growth and dispersal rates and other physical attributes. In contrast, this study examined the effects of extrinsic factors, specifically herbivory by white-tailed deer (Odocoileus virginianus) and competition with an invasive vine, Lonicera japonica, on a rare forest herb, Trillium reliquum and its more common congeners, Trillium maculatum and Trillium cuneatum. We used a factorial design involving deer exclusion and honeysuckle removal to determine effects on relative growth of rare and common trilliums. We found that a common trillium was more susceptible to herbivory than T. reliquum in one of the three sites with a similar trend in a second site and no effect in the third. Deer also significantly reduced relative leaf area (a measure of growth) for all species, reduced the probability of subadult transitions to reproductives, and increased the probability of nonemergence in two sites. While deer had a significant effect in this study, there was no detectable effect of honeysuckle presence on growth for any species of trillium during this time period. Our results show that the long-term management of white-tailed deer will be important to the conservation of spring ephemeral herbs such as T. reliquum, T. cuneatum, and T. maculatum.