Master Gardeners of Northern Virginia

culm [ kuhlm ] noun: the stem of grasses, sedges, rushes, and cattails

Culms is the term used to describe the stems of the monocotyledonous plants called graminoids, as in Poaceae (grasses), Cyperaceae (sedges), Juncaceae (rushes), and Typhaceae (cattails).

Grasses

The culms of grasses have nodes (joints), which are somewhat swollen, and internodes. The leaves emerge from the nodes, with the sheath on one side of the culm and the blade on the other, wrapping it so tightly the culm is unseen at that point. The culms are usually hollow between the nodes, are unbranched, and usually end in an inflorescence.

Smithsonian National Zoo’s Tian Tian bites a bamboo culm in half
after rejecting the larger culm (showing nodes and hollow internode).
Giant bamboos are the tallest of grasses. Photo © Mary Free

Grass Structures
Courtesy Oregon State University

Cross-section of a culm of grass,
probably invasive Miscanthus sinensis (Chinese silver grass).
Photo © Mary Free

A culm of native Chasmanthium latifolium (river oats)
showing leaf blade and open sheath.
Photo © Mary Free

Native Chasmanthium latifolium (river oats) culms
showing nodes, internodes, blades, and sheaths and
terminating in nodding, pedunculate panicles of spikelets.
Photo © Mary Free

Sedges and Rushes

Sedge culms are triangular and solid, with the leaves in three rows. Those of rushes are round and solid or pithy.

Fertile culms of native Carex blanda (common woodland sedge)
terminate in pedunculate inflorescences. Note the loosely wrapped leaf sheath.
Photo © Elaine Mills

Culm of Carex glaucescens (southern waxy sedge)
terminating in inflorescence.
Photo © Elaine Mills

Carex muskingumensis ‘Oehme’ (muskingum sedge)
demonstrating 3-ranked leaves.
Photo © Elaine Mills

Characteristic of rushes are solid, (mostly) round, nodeless stems (culms),
like those of native Juncus effusus (common rush) shown with flowers in July.
Photo © Elaine Mills

Rounded culms of non-native Juncus inflexus ‘Blue Arrows’ (hard rush)
in one of the huge planters along Flower Garden Drive at Longwood Gardens.
Photo © Elaine Mills

Cattails

Cattail culms are also round, leaves emerging from the culm or plant base, and with male and female flowers on the same culm. The larger female inflorescences are below the smaller male flowers near the end of the stem. These velvety heads turn into wind-borne fluff as the seeds ripen. Cattails grow in wet places almost all over the world. While they can be invasive, they also have ethnobotanical uses by indigenous people and are used in silage, paper-making, and for other purposes.

Tyhpha latifolia (common cattail)
at Meadowlark Botanical Gardens in September.
Photo © Elaine Mills

Culms of Tyhpha spp. (cattails)
in the Mount Vernon Trail swamp in November.
Photo © Christa Watters

Culms of Tyhpha spp. (cattails) with fruiting heads
in the Mount Vernon Trail swamp in November.
Photo © Christa Watters

References

Bedish JW. 1964. Studies of the germination and growth of cattail in relation to marsh management. Iowa State University, Digital Repository : https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=17856&context=rtd.

Grass Structures. Forage Information System, Oregon State University Department of Crop and Soil Science. (https://forages.oregonstate.edu/regrowth/how-does-grass-grow/grass-structures, accessed October 23, 2021).

Grasses, Sedges, Rushes. Ecological Atlas of Denali’s Flora. Denali National Park and Reserve.(https://ecologicalatlas.uaf.edu/index.php/browse-plant-species/atlas-group/?nps_gf=4&nps_num=1&overview=1, accessed October 23, 2021).

Illinois Wildflowers, © 2002-2020 by John Hilty. (http://www.illinoiswildflowers.info/index.htm accessed October 23, 2021).

Lab 8. Monocots, Commelinids: Poales (Poaceae, Cyperaceae, Juncaceae, Typhaceae); Arecales (Arecaceae). Department of Plant Sciences. University of California, Davis.