This wetland species develops spongy stems and enlarged bases when it grows in water that does not fluctuate. It does not take on this form when it grows in coastal plain ponds where water levels fluctuate from year to year (Enser 2000).
There are nine existing populations, most of them with hundreds of plants. There are five additional populations known from the early 1900s which have not been rediscovered. Three additional populations are considered extirpated.
Most populations have had one revisit and seem stable although the number of plants detected is somewhat dependent upon the water level of the ponds.
This plant has always been rare in New York and the number of populations are stable. Even though some populations have been eliminated on western Long Island, new populations have been found on eastern Long Island.
Some ponds have seen too much development along the shoreline which threaten populations with direct disturbance by trampling and ATV use. The invasion of Phragmites is also a threat to a few populations. This plant occurs in the most susceptable section of the pond margin.
The pondshores need to be protected from direct disturbance by ATVs and excessive trampling. Exotic invasive species must be prevented from colonizing the shores and present populations must be eliminated. A natural buffer of at least 200 feet should be established around the ponds to prevent excessive runoff and pollution events.
These plants occur in saturated to flooded acidic sands and peat of coastal plain pond shores, swales, and wet meadows of the coastal plain.
This species was originally known from western Nassau County to eastern Long Island but presently known only from Suffolk County.
The species is considered rare in every state that it occurs. It occurs primarily on the Atlantic coastal plain from Georgia to southeast Massachusetts. Its distribution is more scattered in the southern portion and more concentrated in New Jersey and to the north. There are several disjunct populations in the north central United States from Kentucky north to Michigan.
Creeping St. John's wort is a rhizomatous herbaceous plant that grows 3-8 decimeters tall. It usually occurs in large clumps with many stems. It has opposite, linear, to narrowly elliptic leaves that are 3-6 centimeters long and 5-10 millimeters wide, 4-6 times as long as wide. Each leaf has a tiny white point at the tip and is tapered at the sessile base. The margins are without teeth and turned under. There are usually many flowers in the inflorescence. The sepals are lanceolate to ovate and 2-7 millimeters long, widest at or below the middle. The bright yellow petals are 6-8 millimeters long. The fruit is a one-chambered capsule that is 4-6 millimeters long and gradually narrowed to the beak.
Even though these can be identified by their leaves in their pondshore habitat it is best to identify them in flower or fruit.
Hypericum ellipticum looks the most like this species but its leaves are flat and not turned under on the margin and the tips are not pointed but rounded. They are only 2-3 times as long as wide. The sepals are widest above the middle. They both are plants of wet places, rhizomatous, and with styles that are not separate.
The plants begin flowering in July and are visible through August. Fruits are visible from late August through early October.
The time of year you would expect to find Creeping St. John's Wort flowering and fruiting in New York.
Creeping St. John's Wort
Hypericum adpressum Raf. ex W. Bart.
Gleason, Henry A. and A. Cronquist. 1991. Manual of Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York. 910 pp.
Clemants, Steven and Carol Gracie. 2006. Wildflowers in the Field and Forest. A Field Guide to the Northeastern United States. Oxford University Press, New York, NY. 445 pp.
Crow, Garrett E. and C. Barre Hellquist. 2000. Aquatic and Wetland Plants of Northeastern North America: A revised and enlarged edition of Norman C. Fassett's a Manual of Aquatic Plants. Volume One: Pteridophytes, Gymnosperms, and Angiosperms: Dicotyledons. The University of Wisconsin Press. Madison, Wisconsin. 536 Pages.
Enser, Richard W. 2000. Hypericum adpressum Barton, Creeping St. John's-wort. New England Plant Conservation Program Conservation and Research Plan. New England Wild Flower Society, Framingham, MA 01701.
Fernald, M.L. 1950. Gray's manual of botany. 8th edition. D. Van Nostrand, New York. 1632 pp.
Holmgren, Noel. 1998. The Illustrated Companion to Gleason and Cronquist's Manual. Illustrations of the Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York.
New York Natural Heritage Program. 2010. Biotics database. New York Natural Heritage Program. New York State Department of Environmental Conservation. Albany, NY.
New York Natural Heritage Program. 2019. New York Natural Heritage Program Databases. Albany, NY.
Weldy, T. and D. Werier. 2010. New York flora atlas. [S.M. Landry, K.N. Campbell, and L.D. Mabe (original application development), Florida Center for Community Design and Research http://www.fccdr.usf.edu/. University of South Florida http://www.usf.edu/]. New York Flora Association http://newyork.plantatlas.usf.edu/, Albany, New York
This guide was authored by: Stephen M. Young
Information for this guide was last updated on: September 6, 2012
Please cite this page as:
New York Natural Heritage Program. 2019. Online Conservation Guide for Hypericum adpressum. Available from: https://guides.nynhp.org/creeping-st-johns-wort/. Accessed October 16, 2019.