Illustration by Kathleen Garness
A Case Study
This carnivorous wetland species grows in nutrient-poor wetlands and consumes insects to supplement its diet.
Life History: Perennial
Illinois Status: Endangered
Populations monitored: 7
Subpopulations monitored: 8
Counties monitored: 2
Purple pitcher plant (Sarracenia purpurea) is a carnivorous native plant restricted in Illinois to the northeast corner of the state1. Pitcher plant rosettes consist of highly modified tubular leaves that range from 3 to 8 inches long, each topped by a flared hood that allows rainwater to collect inside. The exterior of these pitcher-like leaves is green with purple veins. Inside are tiny downward-facing hairs that prevent the escape of any insects that have fallen in. The pitchers contain digestive enzymes that help the plant to digest and absorb nutrients from its insect prey1,2.
Habitat and Range
Purple pitcher plant is the most widespread Sarracenia species in North America, ranging across the lower tier of Canada, and Maine south to Georgia, and west to Minnesota3. This range has been revised by some authors who remove Gulf Coast populations, considering them to be a separate species, Sarracenia rosea4,5. Purple pitcher plant typically grows in isolated, nutrient-deficient bogs and fens6. In Illinois, this species was historically documented in three counties in the northeastern corner, though it is now extirpated from one of those counties7. Of the seven populations known and monitored by POC, two are now presumed extirpated. The habitats in these extant populations are quite variable – from bogs to sedge meadows and marl-rich wetlands. Contrary to popular understanding, purple pitcher plant does not require acidic conditions for growth6,8.
In Illinois, purple pitcher plant blooms from May through June, with only one flowering stalk emerging from each plant7,9. Individual plants are reported to live as long as 20 to 50 years, and plants can reproduce clonally by rhizome offshoots 1,8. Reproduction by seed is rare and dispersal distances are small, which brings into question how plants initially colonized isolated wetlands10,11. Variability in pitcher size and shape seems to be determined more by soil biochemistry than genetics9,12,13.
Although the plant’s pitchers catch and digest insects, such as ants, flies, grasshopper, crickets, and snails, purple pitcher plants also benefit many insect species. Ants, bees, butterflies, moths, and wasps all feed on the nectar produced by their flowers. Beetles and spiders use pitchers as kill sites, as many of their prey are lured there by pitcher-born nectaries, and some spiders may spin a web within the pitchers to catch insects that fall inside. Certain insects have even found shelter where other insects perish. For instance, larvae of a small, non-biting mosquito (Wyeomyia smithii) and a midge (Metriocnemus knabi) live in the liquid at the bottom of the pitcher plant, withstanding the digestive enzymes that kill other insects1,2,8,14. Microorganisms living inside the pitchers contribute to decomposition and nutrient uptake by the plant14.
Purple pitcher plant is threatened by a host of factors. Degradation of its wetland habitats occurs when land is converted for cultivation, housing, or other development. Invasion by exotic species can crowd and shade-out pitcher plant populations, as well as alter the hydrology of sensitive wetlands. Hydrological modification and nutrient pollution of the surrounding landscape can be as damaging as direct habitat loss6. Further, climate change is a very real threat to the persistence of pitcher plants as a result of their poor dispersal ability and tendency to grow in isolated habitats6,10,. Complicating all of these factors is the low genetic diversity found among populations, suggesting a risk to populations that experience sudden, stressful conditions12. Lastly, illegal collection of wild plants can have a significant detrimental effect and has resulted in local extirpation in some cases8.
Purple pitcher plant is listed as endangered in Georgia and Illinois, and a yellow form (S. purpurea forma heterophylla) is listed as threatened in Michigan. In Illinois, the species has been considered endangered since 1980 as a result of its habitat restrictions and low population numbers15. Although a change in status from endangered to threatened was considered by the Endangered Species Protection Board in 2013, this motion failed because of continued threats to bog and fen habitats16.
Monitoring and Research
POC has monitored pitcher plant populations in two counties of northeastern Illinois for 11 years. Since 2004, POC has collected data on seven populations, two of which no longer support plants. Research conducted by graduate student and POC volunteer Dan Fink leveraged this baseline data6. With additional POC volunteers providing field assistance, he counted 2,540 plants in all five extant pitcher plant populations in 2011. He found that populations were all situated in the Wheaton morainal area of Lake and McHenry Counties, but widely spread across a 30-kilometer area. Associated species were different between sites, highlighting the variety of habitats in which the plants are found. Further, Illinois plants exhibited morphological variation across sites, which is likely due to variation in the soil chemistry rather than to genetic differences12.
Monitoring of this endangered plant and its vulnerable habitat by POC has resulted in long-term data on the few remaining populations. Since northeastern Illinois is the only region of the state with extant populations, monitoring data collected by POC volunteers provides a critical resource for researchers and decision-makers who can use it to better understand how to conserve this species. The onset of anthropogenic climate change further emphasizes the importance of this work. It is critical to track and conserve species, like purple pitcher plant, likely to be sensitive to the changes in precipitation and temperature predicted to occur as the earth warms. As a result of these factors, this species remains a focus of POC monitoring and data collected by POC continues to be critical for effective conservation.