Reproductive Ecology of Rudbeckia Fulgida Ait. Var. Sullivantii (C. L. Boynt and Beadle) Cronq. (Asteraceae) in Northeastern Illinois1

By Scott, Lynne Molano-Flores, Brenda

SCOTT, L. (University of Illinois, Natural Resources and Environmental Sciences, W-503 Turner Hall, 1102 S. Goodwin, Champaign, Illinois, 61820, USA) AND B. MOLANO-FLORES (Illinois Natural History Survey, 1816 S. Oak St., Champaign, Illinois, 61820, USA). Reproductive ecology of Rudbeckia fulgida Ait. var. sullivantii (C. L. Boynt and Beadle) Cronq. (Asteraceae) in northeastern Illinois. J. Torrey Bot. Soc. 134: 362-368. 2007.- Rudbeckia fulgida var. sullivantii (Sullivant’s Coneflower) is a target species for conservation and restoration at the Midewin National Tallgrass Prairie in Will County, northeastern Illinois, due to its classification as a Regional Forester’s Sensitive Species by the United States Forest Service (USFS; i.e., a species for which population viability is a concern because of a significant current or predicted downward trend in population numbers/density or in habitat capability that would reduce a species’ existing distribution). We collected data on the reproductive ecology of this species including its breeding system, seed set, and flower visitors at seven populations in northeastern Illinois from 2002-2004, to support a conservation plan for the species on USFS lands. We found that R. fulgida var. sullivantii is mostly self-incompatible. Percent seed set ranged from 26.1 to 69.5 with the great majority of populations having over 45 percent seed set. Insects from 32 families were identified as flower visitors to R. fulgida var. sullivantii. Six out of seven populations had between 18-22 insect families and one population had 11 insect families as flower visitors. We concluded that the reproductive ecology of Rudbeckia fulgida var. sullivantii is not the leading cause for its decline in northeastern Illinois. Key words: Midewin National Tallgrass Prairie, reproductive ecology, Rudbeckia fulgida var. sullivantii, sensitive species, Sullivant’s coneflower.

Plant conservation strategies are often more reactive than proactive. One reason for this is that conservation plans are usually not implemented until a species is at the verge of extinction. Unfortunately, in most cases information on reproductive biology, ecology, genetic diversity, and even hybridization potential is lacking for many species that are rare (i.e., threatened or endangered). For example, sexual plant reproduction (i.e., fruit and seed set) is essential for the maintenance of most populations, and for several rare species it has been demonstrated that limited pollination and self-compatibility issues can lead to a decrease in the seed set of these plants (e.g., DeMauro 1993 [Hymenoxys acaulis var. glabra], Evans et al. 2004 [Dicerandra christmanii]). Having an early understanding of this information could aid in the successful preservation and management of these species.

For many rare species or species of concern (i.e., a species not yet listed as threatened or endangered, but in danger of becoming listed if no action is taken such as Regional Forester’s Sensitive Species) a more proactive approach can be taken to avoid the risk of these species becoming endangered or extinct. A good example of such a species of concern is Rudbeckia fulgida Ait. var. sullivantii (C. L. Boynt and Beadle) Cronq., (Sullivant’s coneflower, Asteraceae). This species is not considered threatened or endangered in the USA even though it has a national ranking of three, meaning it is rare or uncommon (USDA Forest Service 2006). However, the United States Forest Service (USFS) has classified this species as a Regional Forester’s Sensitive Species, a plant species identified by a Regional Forester for which population viability is a concern, as evidenced by a significant current or predicted downward trend in population numbers/density or in habitat capability that would reduce a species’ existing distribution (Forest Service Manual 2005). In the case of R. fulgida var. sullivantii the main threats across its range are: habitat loss as a consequence of development, agriculture, grazing, changes in the hydrology of its habitat as a consequence of these activities, and encroachment by successional vegetation (Molano-Flores 2005).

As with many rare species or species of concern, limited information is available about the biology and ecology of Rudbeckia fulgida var. sullivantii. The few studies that have been conducted focus on the immunomodulating activity of the species (i.e., using plant extracts for immune system therapy; Bukovsky et al. 1998, Kardosova et al. 1998). However, its popular cultivar known as R. fulgida var. sullivantii ‘Goldsturm,’ which is widely used in landscaping, has been extensively studied. This work has focused on seed germination, flower photoperiod, genetic similarity to other cultivars, and commercial production (Yuan et al. 1996, Runkle et al. 1999, Gettys and Werner 2001, Keever et al. 2001).

Two USFS conservation assessments have been written for Rudbeckia fulgida var. sullivantii. The first assessment was completed in 1999 and serves as a conservation strategy, giving specific goals and objectives for this species at Midewin National Tallgrass Prairie (MNTP) in Will County, Illinois (USDA Forest Service 1999). The second assessment gives an overview of the species’ status in each state where it occurs, but focuses most specifically on natural areas that contain the species in Illinois and Indiana (Molano- Flores 2005). Both conservation assessments note an absence of any life history information including breeding system, reproductive success, and associated pollinators. One of the overall goals of Illinois’ MNTP conservation strategy is to “maintain and increase existing populations of R. fulgida var. sullivantii by protecting its habitat (existing and potential), and to do this by using the proper management techniques” (USDA Forest Service 1999).

The intent of this study was to generate data on multiple aspects of the reproductive ecology of Rudbeckia fulgida var. sullivantii to assist in the development of a conservation plan for the species on USFS lands, particularly the Midewin National Tallgrass Prairie. In this three-year (2002-2004) study we collected data on the breeding system (autogamous or xenogamous and self-compatible or self- incompatible), reproductive success (i.e., seed set), and flower visitors for this USFS Regional Forester’s Sensitive Species at the MNTP.

Materials and Methods. SPECIES DESCRIPTION. Rudbeckia fulgida Ait. var. sullivantii (C. L. Boynt and Beadle) Cronq., commonly known as “Sullivant’s Coneflower” or “Orange Coneflower,” is a stoloniferous perennial that grows 3-10 dm tall (Gleason and Cronquist 1991, Molano-Flores 2005). This species has alternate, lanceolate to ovate leaves with sharply dentate margins and primarily pinnate venation (Urbatsch and Cox 2006). There are typically several terminal heads on an individual, each with 2.5-4 cm long orangeyellow sterile rays (Gleason and Cronquist 1991, Urbatsch and Cox 2006). This species blooms in the later summer months from midJuly through late September (Gleason and Cronquist 1991, Urbatsch and Cox 2006). Rudbeckia fulgida var. sullivantii is found in nine states: Arkansas, Illinois, Indiana, Michigan, Missouri, New York, Ohio, Pennsylvania, and West Virginia (USDA NRCS 2004). In Illinois, this species has been reported in 12 counties out of 102 (Molano-Flores 2005). It should be noted that at the study sites (see Study. Sites) the stoloniferous growth of the species was localized, forming discrete ramets (L. Scott, pers. obs.). In addition, based on random amplified polymorphic DNA, high levels of genetic diversity were found in most of the studied populations suggesting that individuals in the studied populations have multiple genotypes (Scott 2005).

STUDY SITES. This study was conducted in seven populations located in Will County, northeastern IL from 2002-2004. Six populations were found at the MNTP (6,815 ha, 41.374[degrees]N, – 88.126[degrees]W) and one at Grant Creek Prairie (GCP: 41.373[degrees]N, -88.191[degrees]W), a 32 ha remnant prairie just west of and adjacent to MNTP. All populations were at least 1.6 km from each other. Three of the six populations at MNTP were found in old pastures, two on woodland edges, and one along a roadside. At MNTP management practices such as cattle grazing and mowing and in GCP prescribed burning have been conducted. Rudbeckia fulgida var. sullivantii populations range in size (based on visual estimates) from very small (< 50 ramets) to large (> 2000 ramets). It should be noted that R. fulgida var. sullivantii is the only variety of R. fulgida found at the study sites. Also, weather conditions during the growing and reproductive period of R. fulgida var. sullivantii at the study sites (May to September) were more similar between 2003 and 2004 than 2002. Total precipitation for May to September was: 2002 = 32.5 cm, 2003 = 55.6 cm, and 2004 = 57.4 cm (Station 111420 Channahon, Will County; Illinois State Climatologist’s Office 2007).

HEADS/FLORET PHENOLOGY. Heads and floret phenology studies were conducted in Champaign, IL at the Illinois Natural History Survey (INHS) greenhouse and confirmed at MNTP. Fifteen heads, one per plant, were observed to determine the timing and development sequence of the disk florets (corolla, stigma, and stamen) and head (receptacle, ray and disk florets) during July and August of 2003. On average 15 to 20 disk florets were observed across the head. BREEDING SYSTEM. Breeding system treatments were performed at two MNTP populations (MNTP-3 and MNTP-4) in 2003 and 2004. Each of the three treatments described below was conducted in a different set of 30 individual plants (one head per individual) per population. To determine if Rudbeckia fulgida var. sullivantii is an autogamous or xenogamous species, heads were bagged with bridal veil to exclude pollinators (bagged treatment). Heads used for reproductive success (see Reproductive Success) served as the unbagged treatment, allowing for natural pollination (open treatment). To determine if the plants are self-compatible or self-incompatible, geitonogamous hand pollinations were conducted in another set of bagged heads (geitonogamous treatment). Approximately 10 florets per head marked on the corolla with pink nail polish were geitonogamously pollinated. To conduct these geitonogamous hand pollinations, pollen from florets located above florets with bifurcated style and stigmatic papillae were used. Heads for the bagged and geitonogamous treatments were bagged prior to the involucral bracts uncurling and the ray florets extending, to maximize pollinator exclusion. seed set on bagged and unbagged heads was determined as the percent filled, firm achenes out of all possible seeds (floret ovaries) in the head. seed set for heads with geitonogamous hand pollinations was measured as percent filled, firm achenes out of all hand pollinated florets. Data from the two MNTP populations were combined for the analysis. The 2004 data was the only data used for analysis purposes because in 2003 the mesh bags covering the heads too frequently touched the head, moving pollen to and from the styles resulting in pollen contamination. In 2004 the mesh bag design was changed, fixing this problem. A Kruskal-Wallis One Way Analysis of Variance on Ranks test was used to determine differences among treatments, followed by a Dunn’s post hoc test (SigmaStat 1997).

FLOWER VISITORS. Flower visitor observations and collections for Rudbeckia fulgida var. sullivantii were made at MNTP and GCP. Visitors were observed and collected in midAugust of 2003 and 2004. One hour observations were made daily between 09:00 and 16:00 (i.e., 09:00-10:00, 10:30-11:30, 12:00-13:00, 13:30-14:30, and 15:00- 16:00) on seven populations for one week each year. Populations were visited at each of these times during this one week period to obtain a total of five flower visitor observations per population. This observation period corresponded to peak flowering time for the populations at MNTP and GCP. Flower visitor observations were conducted under sunny to partly sunny and warm conditions with the first observation (09:00-10:00) starting in the mid 21[degrees]C and the last observation (15:00-16:00) ending in the mid 32[degrees]C. Insects were identified to the family level using keys and images. To identify the butterflies, images from Bouseman and Sternburg (2001) were used. Keys and drawings in White (1983) and Borror and White (1970) were used to identify the beetles and all other taxa, respectively.

REPRODUCTIVE SUCCESS. From 2002-2004, reproductive success of Rudbeckia fulgida var. sullivantii was examined using six populations at MNTP and one population at GCP. Depending on the population size, between 19 and 30 heads (one per individual) were haphazardly collected from each population in early October. Individuals were collected at a minimum of 91 cm (3 feet) apart to minimize collecting seeds from potentially genetically identical individuals due to the stoloniferous growth of the species. seed set was determined as the percent of filled, firm achenes out of all potential seeds (floret ovaries) in the head. A two-way ANOVA was used to determine differences in percent seed set between years, populations, and their interaction, followed by a Holm-Sidak post hoc test (SigmaStat 1997). To meet the assumptions of normality seed set was square transformed. Although arcsine square root transformation is used to normalize percent data, this transformation did not achieve such purpose because of the skewed nature of the data set. The square transformation, however, did normalize the data.

Results. HEADS/FLORET PHENOLOGY. Studied populations of Rudbeckia fulgida var. sullivantii in northeastern Illinois bloomed from mid- July to late September. This species had multiple heads per plant and each of these heads went through the following phenological stages.

A Rudbeckia fulgida var. sullivantii head took about a month to bloom starting from when the ray florets uncurled to the final disk floret blooming at the apex. In one week involucral bracts uncurled, followed by ray florets extending and then recurving back on top of the bracts. In this time the receptacle became more conical in shape. The perfect, dark purple-brown disk florets matured acropetally, each taking 4-6 days for the corolla to develop. The purple-brown style pushed the pollen up through the corolla tube displaying the pollen, followed by the style bifurcating. If the yellow-orange pollen was not removed from the style branches (via a pollinator), the pollen remained stuck to the tips of the style branches as they separated. Due to the close proximity of each floret in the head, it was possible for pollen to come into contact with the disk floret of the row below. The glabrous style remained bifurcated and developed stigmatic papillae on the upper surface, suggesting receptivity. The style branches continued to curl until the sweeping hairs at their tips almost touch the underside of the branch. The styles remained this way until any lingering pollen turned white (10-14 days). Following this pollen color change, the style soon shriveled inside the corolla tube. This sequence of events means that florets at the base of the head were senescing while florets at the apex were at anthesis. As the head aged, the tips of the ray florets turned a paler yellow color. These greenhouse flower head phenological observations were also confirmed in the natural populations at MNTP.

BREEDING SYSTEM. Seeds were set in all three pollination treatments used to test the breeding system of Rudbeckia fulgida var. sullivantii (bagged, geitonogamous, and open). The Kruskal- Wallis One Way Analysis of Variance on Ranks indicated significant differences among treatments (H = 112, df = 2, P < 0.001; bagged: x = 12.5%, SE = 1.2; geitonogamous: x = 14.3%, SE = 2.2, open: x = 63.2%, SE = 1.3). The open heads showed the highest percent seed set compared to the bagged and geitonogamous treatments (Dunn's post hoc test: P < 0.050 in both cases) and no significant differences were found between bagged and geitonogamous treatments (Dunn's post hoc test: P > 0.050).

FLOWER VISITORS. During the 2003-2004 field seasons, flower visitors were collected from Rudbeckia fulgida var. sullivantii heads. Most of the insects collected were considered generalists (i.e., they forage on many different taxa of plants). Most observed insect visitors belonged to Coleoptera, Diptera, Hymenoptera, and Lepidoptera, although a few Hemiptera were observed. A total of 32 families were identified as flower visitors to R. fulgida var. sullivantii (Table 1). All seven populations observed had between 18- 22 insect families as visitors except population six, which only had 11 insect families (Table 2). The most common insect families observed were Apidae, Cantharidae, Halictidae, Hesperiidae, Nymphalidae, Pieridae, and Syrphidae (Table 1).

REPRODUCTIVE SUCCESS. Overall, mean percent seed set for almost all populations in all years was over 45%, with MNTP-4 having the lowest (26.1%) in 2002 and MNTP-7 the highest (69.5%) in 2004 (Table 2). The twoway ANOVA showed significant differences in percent seed set for years and populations, and the interaction between years and populations was also significant (F = 46.3, df = 2, P < 0.001, F = 13.6, df = 6, P < 0.001, and F = 9.3, df = 12, P < 0.001 respectively).

Table 1. Orders and families of insects visiting Rudbeckia fulgida var. sullivantii heads at Midewin National Tallgrass Prairie and Grant Creek Prairie (August 2003 and 2004).

Discussion. For a conservation plan to be successful, key pieces of information must be known about the species in question. For sensitive, threatened, or endangered plants, this key information includes multiple aspects of the species’ life history such as breeding system, reproductive success, and flower visitors. In this study, we collected this key reproductive information for the USFS Regional Forester’s Sensitive Species Rudbeckia fulgida var. sullivantii.

Our breeding system study determined that Rudbeckia fulgida var. sullivantii is a xenogamous species. This finding is similar to other studies that found R. auriculata (Diamond et al. 2006), R. missouriensis (King and Schaal 1989) and R occidentalis (Florez and McDonough 1974) to be xenogamous too. Floret morphology observations made on R. fulgida var. sullivantii showed floral traits that encourage outcrossing such as the protandrous secondary pollen presentation, which separates floret anther dehiscence from stigma receptivity (Leins and Erbar 1990). While the specific timing of stigma receptivity could not be confirmed in R. fulgida var. sullivantii, morphological indications (i.e., papillae development) suggest receptivity occurs after anther dehiscence (L. Scott, pers. obs.).

Table 2. Total number of insect families for 2003-2004 and mean percent seed set (+- SE) for 2002-2004 for each Rudbeckia fulgida var. sullivantii population surveyed. MNTP = Midewin National Tallgrass Prairie and GCP = Grant Creek Prairie.

Additional breeding system treatments to determine self- compatibility or self-incompatibility showed seeds developed when heads were geitonogamously pollinated, indicating partial self- compatibility. However, seed set levels were low, especially when compared to heads left open to natural pollination. Therefore, overall, results indicate Rudbeckia fulgida var. sullivantii is a mostly self-incompatible species. These results are supported by many other studies that have found self-incompatibility systems to be common in Asteraceae (DeMauro 1993, Messmore and Knox 1997, Mani and Saravanana 1999, Morgan 1999). Other studies on species related to Rudbeckia have shown that selling can occur in spite of self- incompatibility (Aster furcatus in Reinartz and Les 1994; Echinacea angustifolia in Leuszler et al. 1996). In addition, it should be noted that agamospermy has been reported in Rudbeckia species, including R. fulgida var. sullivantii (Nygren 1954). In our field studies and in a controlled experiment in the greenhouse (unpublished data) seeds were found in bagged heads suggesting that agamospermy or selfing (due to floret phenology) is a possibility and should be explored further in the studied populations. In Rudbeckia fulgida var. sullivantii, all studied populations showed relatively high levels of reproductive success (greater than 45% seed set) except for population MNTP-4 in one year (Table 2). This may simply reflect natural variation in that population, especially because in all subsequent years, seed set levels were similar to the other studied populations. The range of percent seed set levels found in R. fulgida var. sullivantii is greater than what has been observed for the rare Rudbeckia auriculata (0.24-31.4%; Diamond et al. 2006), but falls within the range of those found in other members of Heliantheae such as Echinacea angustifolia with seed set ranging from 0-63% (Wagenius 2004) and Helianthus pauciflorus with an average of 60% seed set (McKone et al. 2001), and other Asteraceae such as Arnica montana with 19-97% seed set depending on population size (Luijten et al. 2000), and Hymenoxys acaulis var. glabra with an average of 50% seed set (Moran-Palma and Snow 1997).

While all populations of Rudbeckia fulgida var. sullivantii showed high measures of seed set, the number of insect families visiting the various populations differed. Population MNTP-6 had the fewest number of insect visitor families (11), whereas the other populations all had between 18-22 visitor families. In insect pollinated plants there are many ecological factors that could influence pollinator foraging behavior (i.e., presence or absence) including the physical distance between populations (Morris 1993), size and shape of populations, and the density of floral displays (Kunin 1993, Richards et al. 1999). It is possible that the lower number of insect families visiting population MNTP-6 is due to the small size and low-density floral display of this population. However, seed set results show a sufficient amount of flower visitors were present in the population to maintain high reproductive success for three consecutive years (Table 2). This is probably helped by the generalist nature of the flower visitors and the proximity of population MNTP-6 to other R. fulgida var. sullivantii populations.

Overall the data suggest that Rudbeckia fulgida var. sullivantii populations at MNTP and GCP are reproductively viable suggesting that plant reproduction may not be the main cause for its Regional Forester’s Sensitive Species status at the MNTP. Nonetheless, we would like to mention that gaps in our knowledge of the biology and ecology of this species (i.e., demographic data, population genetics, specific habitat requirements, germination requirements, susceptibility to diseases, and response to disturbances such as fire and grazing) exist, and may explain the species’ decline. For example, a preliminary seed germination study has shown extremely low seed germination (1%) for this species (Scott 2005). If seeds have specific seed germination requirements that can lead to low seedling recruitment in populations, then these populations may not be viable in the long term. Also, research on the effects of cattle grazing on this species at MNTP is showing that flower stem production is being negatively impacted (Susanne Masi, pers. comm.). Finally, another aspect that is under investigation is the impact of the cultivar form of this species (R. fulgida var. sullivantii ‘Goldsturm’) on its conservation. Preliminary data suggest that gene flow (i.e., successful reciprocate crosses) between the wild type and cultivar can occur, but little difference in genetic variation was observed between wild and cultivar populations (Scott 2005). Further research is underway to fill these information gaps which will aid in the development of ex-situ and in-situ conservation plans, allowing for successful management of the species at the MNTP and other USFS lands.

1 This project was funded in part by a grant from the Illinois Native Plant Society.

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Lynne Scott2,3

University of Illinois, Natural Resources and Environmental Sciences, W-503 Turner Hall,

1102 S. Goodwin, Champaign, Illinois, 61820, USA

Brenda Molano-Flores4

Illinois Natural History Survey, 1816 S. Oak St., Champaign, Illinois, 61820, USA

2 We thank Clark Danderson for insect identification and Cassandra Allsup for field (collection of plant and insect specimens) and laboratory (seed germination) assistance. The comments of Geoffrey Levin and anonymous reviewers helped improve the organization and clarity of this manuscript.

3 Current address: Parkland College, Natural Sciences Department, 2400 West Bradley Ave., Champaign, IL 61821, USA.

4 Author for correspondence. E-mail: molano@ inhs.uiuc.edu

Received for publication April 12, 2007, and in revised form July 3, 2007.

Copyright Torrey Botanical Society Jul-Sep 2007

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