CPC Plant Profile: Orono Sedge
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Plant Profile

Orono Sedge (Carex oronensis)

A close-up of the inflorescences of Carex oronensis. Photo Credit: Alison Dibble
  • Global Rank: G3 - Vulnerable
  • Legal Status: N/A
  • Family: Cyperaceae
  • State: ME
  • Nature Serve ID: 145130
  • Date Inducted in National Collection: 05/01/1999

Carex oronensis is a sedge that grows in loose clumps up to a meter tall. It is endemic to a small area of Maine, and Maine's only known endemic plant species. Most of its 58 known populations contain few stems, with only a handful of populations encompassing more than fifty stems. Growing in fields, meadows, roadsides, and clearings, the plant is susceptible to disturbance and habitat conversion for development. It is regarded as imperiled in Maine because of its very limited distribution. Research and Management Summary: A handful of individuals and institutions have performed research on this species, and the New England Wild Flower Society is monitoring populations in Maine. Plant Description: This sedge is a member of the section Ovales in the Carex genus, and has the typically rounded inflorescences and winged perigynia (sacs enclosing the ovary) of that group. Three to four leaves, each 2-4 mm wide, occur on each fertile clump. Its sharply angled stems grow much taller than the leaves, which are narrow 3-5 mm wide). Well-developed scales are as long as the perigynia, which themselves are narrow and 2.9 to 4.3 mm long and 0.9 to 1.4 mm wide with straight styles and 2 red-brown stigmas (Fernald 1950, Gleason and Cronquist 1991, Haines and Vining 1998, Dibble and Campbell 2001). Mature perigynia are required to distinguish C. oronensis from C. scoparia var. tessellata or C. ovalis, but multivariate analyses of traits show that the species is clearly distinct (Dibble and Campbell 2001). A rust-colored blotch on the adaxial surface of the perigynium is a useful, unique field character. The roots and block and fibrous. The haploid chromosome number is n = 34 (Dibble and Campbell 2001) or n = 37 (Rothrock and Reznicek 1996).

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  • 09/07/2020
  • Propagation Research

The New England Wild Flower Society (Framingham, Massachusetts) has determined that fresh and dried seed, given moist refrigeration, germinates well. Fresh seed can germinate (but does so poorly) without a cold treatment.

Nature Serve Biotics
  • 05/02/2017

Endemic to the Penobscot River Valley, Maine (and a few other areas in the north-central part of the state). There are many small populations but only 3 or 4 with more than 60 plants each. Most populations occur on eminently developable sites and are threatened by land use changes. One of the largest populations was plowed under in the summer of 1991.

Elizabeth J. Farnsworth
  • 01/01/2010

Many very small populations are scattered around the state, often occurring in areas that are easily subject to development or habitat conversion. One of the largest known populations was lost to plowing in 1991 (NatureServe 2001). Only four of the kn

Elizabeth J. Farnsworth
  • 01/01/2010

At least 58 populations are recorded. In a survey between 1987 and 1998, 2862 individual plants were recorded (Dibble and Campbell 2001).

Elizabeth J. Farnsworth
  • 01/01/2010

The New England Wild Flower Society (Framingham, Massachusetts) has determined that fresh and dried seed, given moist refrigeration, germinates well. Fresh seed can germinate (but does so poorly) without a cold treatment. Dr. Alison Dibble (U. S. Forest Service, Bradley, Maine) completed her Master's thesis on Carex oronensis and extensive field surveys for the species (Dibble 1991, Dibble and Campbell 2001).

Elizabeth J. Farnsworth
  • 01/01/2010

Volunteer task forces of the New England Plant Conservation Program of The New England Wild Flower Society (Framingham, Massachusetts) monitor populations of Carex oronensis in Maine. Dibble and Campbell (2001) mention that mowing and/or timber harvest occur on some of the public lands where Carex oronensis occurs -- activities that could help maintain open habitats for the species, if conducted appropriately.

Elizabeth J. Farnsworth
  • 01/01/2010

Studies elucidating the ecology and habitat requirements of this taxon are critically needed

Elizabeth J. Farnsworth
  • 01/01/2010

Long-term seed storage studies and techniques for propagation and reintroduction are needed


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Taxon Carex oronensis
Authority Fern.
Family Cyperaceae
CPC Number 780
ITIS 39734
Common Names Orono sedge
Associated Scientific Names Carex oronensis
Distribution Known from ca. 40 towns in six counties in Maine. The plant is most common in the Penobscot River valley; the type specimen is from Orono (New York Botanical Garden 1891). two small populations occu
State Rank
State State Rank
Maine S3

Carex oronensis grows along road-sides, fields, meadows, power lines, river shores, swales, woods roads, gravel pits, and other clearings (Haines and Vining 1998, Dibble and Campbell 2001). The sedge may inhabit wetlands or uplands. Many populations occur in highly disturbed sites, including hay fields that are mown. The plants appear to prefer mesic areas with high light exposure. The largest populations and the most robust, reproductive stems occur in bright sun, while shaded plants are smaller and less vigorous (Maine Department of Conservation 1999). Associated vegetation includes: several Carex species (C. scoparia, C. tenera, and C. tincta being the most common sympatrics); and early-successional herbs such as Rumex acetosella, Leucanthemum vulgare, Ranunculus acris, Anaphalis margaritacea, Achillea millefolium, Phleum pratense, Vicia cracca, Juncus spp., Luzula spp., Panicum spp., Solidago spp., Rubus idaeus, and Spiraea alba (Dibble and Campbell 2001).

Ecological Relationships

Very little has been published as yet on the ecology of this species. Pollination, as with most sedges, is likely through wind. Carex oronensis is usually protogynous (female flowers emerge first), but stigmas and anthers can be produced at the same time, in May to mid-June. Dibble and Campbell (2001) report that mean fruit set, pollen germination, and pollen viability can exceed 70%, while seed germination averages about 28%. Seeds are likely dispersed by wind, water and gravity from late June through fall. Given its habitat of largely disturbed areas, the plant appears to be intolerant of shade or intense competition with other vegetation (Maine Department of Conservation 1999). However, the species appears to tolerate a wide array of hydrological conditions; its unique physiology warrants further study.

Common Name Name in Text Association Type Source InteractionID
Lead Institution State Reintroduction Type Year of First Outplanting

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