Plant Species Biology Summary for Bigleaf Snowbell Bush
Illinois Department of Natural Resources
Division of Natural Heritage

The following information is derived from monitoring records of the Illinois Department of Conservation for Illinois' only known extant population of this species which is in Alexander County. It is based on data from 1987 thru 1990. The population is a dense circular clone that covers an area of about 246 square meters. The largest stems are near its center. It is in a small forested ravine with a southern exposure. Counts of stems over 1 meter tall range from 61 in 1988 to 96 in 1990 with numerous shorter stems uncounted. From 1987 thru 1989, as few as 4 and as many as 6 of the largest stems flowered. The stand is at an elevation of 420 feet.

Species: Styrax grandifolia, Bigleaf snowbell bush.

Compiler: John Schwegman, Illinois Department of Natural Resources

Date of Most Recent Update: January 17, 1992

Range of Natural Communities: Mesic upland forest.

Range of Plant Communities: Beech-Cucumber Magnolia-Sweet Gum

Range of Soil and Substrate: Silt Loam.

Range of Slope and Aspect: 11 degree slope, 240 degree (SW) aspect.

Range of Shading or Crown Cover: 80%.

Flowering Dates in Illinois: 5-15-87 and 5-18-88 (18th judged 10 days past peak of flowering in 1988).

Fruiting Dates in Illinois: None (4 flowered in 1989 but no fruits present on July 27). No check for fruit was made other years, but no evidence of fruits from the previous year was ever present at monitoring time.

Known Phenotypic Variation: None noted.

Known Pollinators in Illinois: None observed.

Reproductive Mode: The clone appears sexually sterile with no fruits having been observed in four years of monitoring (3 years of flowering). The clone may be a single individual and may be self incompatible. It forms a dense stand, apparently by root or rhizome sprouts which appears to be its primary form of reproduction at Illinois' only site.

Known Conditions for Sexual and Asexual Reproduction: The clone failed to flower in 1990 after a winter low temperature of -20 F and a late spring freeze. Thus unusual cold conditions can prevent the chance for sexual reproduction. These conditions did not hinder asexual reproduction. Cross pollination may be necessary for seed production. There has been no opportunity to observe the conditions necessary for seedling establishment since no seeds have been seen.

Known Diseases: None observed.

Known Grazers and Parasites: Deer browsing was noted in 1988 and 1989, with 5 plants at the edge of the clone completely defoliated by them in 1988. No other grazers noted.

Known Problems with Exotic Species: Japanese honeysuckle and multiflora rose occur along the edge of the clone without serious impact. Most of the multiflora rose was hand pulled in 1987.

Known Competition with Native Plants: Sassafras and flowering dogwood occur within the clone and are competing with it.

Known Response to Fire: Unknown.

Known Mortality Factors: Most stem mortality appears due to competition with other stems of the clone. After the extreme drought of 1988 only one standing dead stem was found the following spring. After the severe cold and late freeze of the '89-'90 winter only 4. This indicates no significant mortality from cold or drought.

Known Shifts in Plant Vigor: Plants failed to flower after severe winter cold and a late freeze.

Summary of Apparent Factors Regulating Size and Health of Populations:

The population is not reproducing sexually, possibly because it is a single individual and is self incompatible. Cold weather prohibits flowering in some years. Why the clone does not expand asexually is unknown. Competition with exotic plants and native woody clone forming species such as sassafras may be a problem in the future. It appears to be a relict of a warmer climatic time that is now isolated and unable to reproduce sexually and spread to new sites. Some climate-related impacts on sexual reproduction (seed germination or seedling establishment) may account for senescence of the species and the condition we see today. The rarity of this species does not appear to be related to human activities.