Reproductive Biology of Stylisma pickeringii (Convolvulaceae), an Endangered Plant of Illinois Sand Prairies

The sand prairie is a unique ecosystem in the state of Illinois, being the habitat for many interesting plants and animals not found elsewhere in the state. One such plant is the state-endangered Stylisma pickeringii (Torr. ex M.A. Curtis) Gray var. pattersoni (Fern. & Schub.) Myint (Convolvulaceae), also known as Patterson\u27s bindweed or Patterson\u27s dawn flower. It currently is found in only three Illinois counties—Cass, Henderson, and Mason. Presently, two of the three populations of S. pickeringii are located on private lands. Very little information is known about the reproductive biology of S. pickeringii var. pattersoni. Thus, the purpose of this research was to gain more information regarding its seed, seedlings, establishment, and regenerative potential. The objectives of this study were to examine scarification techniques to find an effective and efficient method to scarify seeds, determine what factors affect seed color, compare germination of different seed colors of different harvest years, establish a population on state-protected land in Illinois, investigate insect visitation to flowers, and describe flower aspects including morphology and longevity of S. pickeringii. Five scarification techniques (basal cut, sandpaper shakes, sulfuric acid, sand shakes, and sonication) were examined to determine the best scarification method. The percent of each seed color (green, yellow, tan, and maroon) produced and percent germination of each seed color in different harvest years (1998, 1999, 2000, and 2001), and weights, volumes, and viability of each seed color were conducted to determine if variability exists among seed color and harvest year. Seeds on different stem sections (proximal, middle, distal, and side branches) and seeds collected at various intervals after flowering (3, 6, and 9 weeks in 1999; 4 and 7 weeks in 2000), and seeds harvested on different dates (August 20 and September 9, 1999; August 21 and Septembe 20, 2001) were studied to determine if age and harvest time influence seed color. Seed longevity, seedling density, and seedling morphologies were examined to gain information pertinent to establishing the plants on protected land. An establishment study was conducted using two harvest years and scarifications. Flower density data were collected to determine peak flowering. Insect collections were conducted to determine if there were temporal and/or seasonal differences in insect visits. Pollen of S. pickeringii was collected from insect visitors to its flowers to compile a list of possible pollinators. Flower morphology and longevity also were examined to describe flower aspects. Research was conducted in Mason County, Illinois. Scarification affects germination of S. pickeringii. Four techniques (basal cut, 48 h sandpaper shake, 120 min sulfuric acid soak, and 72 h sand shake) provided high germination. More yellow seeds are produced than other seed colors. Also, more yellow seeds are viable than other seed colors. Age and harvest time did not influence seed color. Establishment after one season\u27s growth did not differ for fall or spring plantings. Over 18 genera of insects visited flowers of S. pickeringii with Apis mellifera and Heterostylum croceum being the most frequent. Frequency of insect visits differed throughout the season and by time of day. Although some variation was found in the average diameter of pollen collected from insect bodies and from S. pickeringii flowers, the general appearance of all pollen grains was similar. Flowers of S. pickeringii, although smaller than many other species in the family, are typical of Convolvulaceae, being white, funnel-shaped, complete flowers with radial symmetry. Flowers are five-merous. Flowers remain open for one day. This research will aid in the understanding of S. pickeringii seed production, germination, seedling establishment, and plant regeneration via seed. A better understanding of the reproductive biology of S. pickeringii will lead to better management decisions of this endangered plant and other sand prairie species