Helianthus porteri, Porter’s Sunflower, is a highly specialized sunflower endemic to the harsh conditions of granitic outcrops. It is found at only two sites in North Carolina. One of these is a low elevation granitic dome called Rocky Face Mountain, in Alexander County. In mid September, Alexander and surrounding counties in the Northern Piedmont were in the grip of a serious drought. Even Helianthus porteri was affected, and the fall bloom subdued.
Helianthus porteri was by far the most visible of the endemic plants at Rocky Face Mountain, and its yellow blooms were seen throughout the base, slopes and top of the granite dome, although in reduced numbers this year. The group pictured below at the base of the dome was blooming well, even while the foliage was withering and drooping.
The H. porteri on the slopes were not faring as well, especially those at the top of the slopes. Some clusters of plants had died, but most were still surviving. The following plants were typical of many seen – badly stressed but capable of complete recovery with a little rain. In the first photo, the slope behind and the small patch of soil containing the plants can be seen. The second photo is a closer view of the plants.
Some of the non-endemic plants, like the American Beautyberries (Callicarpa americana), were in a terminal, dehydrated state, especially those with a full sun exposure.
From the base of the dome, a group of H. porteri could be seen blooming at the top of the cliff.
A view of the same group from the top of the dome revealed that the plants were rooted in a large, horizontal crack in the granite. They were also located at the base of an elevated slope, in a perfect position to catch moisture that would run down the slope from light showers. These plants looked normal and were well hydrated even though exposed to full sun.
Another healthy group of H. porteri was seen growing from the convergence of two cracks, where rain water would run down from two sections of the slope to flow into the cracks.
Even without the advantage of a slope to bring moisture, several clusters of H. porteri were growing from cracks in a horizontal surface of the granite. Whatever amount of soil was present in the granite cracks, it was completely protected from the drying effects of direct sun. In full sun exposures, the plants growing from cracks in the granite were clearly doing better than those growing in the patches of soil on the granite surface.
Phemeranthus teretifolius, the Quill Fameflower or Appalachian Rock-pink, was another endemic plant that was surviving the drought well. Its summer green color had turned to an autumn red, but the plants looked well hydrated. A large group were found growing in an area of hardened gravel at the base of the dome. Remarkably, it was difficult to scrape up any soil at all in this area, which looked like the surface of a gravel road.
Helianthus porteri is somewhat unusual in that it is an annual in a genus that is mostly perennials. During his Ph.D. work at the University of North Carolina at Chapel Hill, Abram Mellinger built an artificial granite flatrock to establish and study a colony of Helianthus porteri. He soon had a large, flourishing colony which he maintained and studied over a period of years. In 1968, a prolonged and extreme drought resulted in the deaths of all the plants before they were able to set seed. The next spring, the colony was completely restored naturally from the seed bank that it had established over the previous years.
Helianthus porteri is not native to North Carolina, but was brought accidentally from Georgia to Rocky Face Mountain and the flat rocks of Mitchell Mill in Wake County in 1959, as part of an ecological experiment that focused on Diamorpha smallii (Elf Orpine). For over 50 years, Helianthus porteri has remained and thrived in these two locations.
Mellinger, A. C. 1972 Ecological Life Cycle of Viguiera porteri and Factors Responsible for Its Endemism to Granite Outcrops of Georgia and Alabama Ph.D. Thesis, UNC at Chapel Hill Botany Department
Note that Viguiera porteri was an older designation, which was reclassified to Helianthus porteri.