General Species Description
- E. obtusa is a native annual sedge that is medium-sized, 5-50 cm tall, and has loosely tufted needle-like stems. The stems are ribbed, 0.5-2 mm thick, and while the plant appears leafless, it does have basal leaves that wrap around the stem like dark sheaths. Plants have no rhizomes.
Leaves
- While the plant appears leafless, it does have a small, thin modified leaves that wrap around the base of the stem like dark sheaths.
Inflorescence/Flowers
- E. obtusa has an oval to cylindrical brownish flower spike 5-13 mm long with 40-80 flowers (sometimes as many as 100), each with 2 stigmas. Individual flowers are found within purplish to brownish scales 1.7-2.5 mm long with green midribs and transparent margins.
Fruits
- Fruit is a dark brown achene 1-1.5 mm long that is smooth, triangularly shaped and tapered at base. It is surrounded by 6-7 bristles equal in length to the achene. E. obtusa flowers from June to September.
Habitat
- E. obtusa is found in wet prairies, shallow ponds, muddy swamps, lakeshores and other areas where the water usually dries by the end of the season. It is found along with two related species, needle spikerush (E. acicularis) and the larger creeping spikerush (E. palustris). The former, unlike E. obtusa and E. palustris, tends to favor areas that remain wet through the season. All three Eleocharis species are associated with other obligate species like duckweeds (Lemna species) and bulrushes (Scirpus species).
Range
- E. obtusa is found throughout the Pacific Northwest, and commonly throughout all counties of Northwestern Oregon except Tillamook, Clatsop and Clark.
Similar Species
- At first glance, E. obtusa can easily be confused with the two other Eleocharis species, E. acicularis and E. palustris. Careful consideration of these plants, however, will reveal notable differences. E. acicularis at 3-12 cm tall is the smallest of the three species and forms mats of branching rhizomes. E. palustris can reach heights of 1 m and grows in small clumps along a dark brown rhizome. The flowering spike is also somewhat darker and is often spear-shaped. Other plant species that may also be mistaken for E. obtusa are the plantains (Plantago species). While they also possess flowering spikes (although typically much larger in relation to the size of the stem), closer inspection will reveal medium to large leaves at the base of the plants.
Ecological Value
- The stems and seeds of E. obtusa are eaten and used as nesting material by a variety of birds and its roots eaten by some mammals. When plant populations are dense, it also helps anchor the soil to the ground providing erosion control for water banks.
Human Value
- N/A
References
- Guard, Jennifer. Wetland Plants of Oregon and Washington. 1994. Seattle Audubon Society. A Field Guide to the Common Wetland Plants of Western Washington and Northwestern Oregon. Seattle Audubon Society, WA. 1997.
This page was created by: Angeline Perla, August 1998
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