Culm

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.

Bei Bei shows his visitors the inside of a bamboo culm with its solid nodes and hollow internode at the Smithsonian's National Zoo.

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

Grass Structures Courtesy Oregon State University

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

Glabrous culms (nodes and internodes), blades, and sheaths of Chasmanthium latifolium (river oats)

Left to right: pandas with bamboo (Tian Tian and Bei Bei), culm cross-section, grass structures, Chasmanthium latifolium (leaf and culms with inflorescence).

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 — Left to right: *Carex blanda*, *Carex glaucescens*, *Carex muskingumensis* ‘Oehme,’ *Juncus effusus*, *Juncus inflexus* ‘Blue Arrows.’

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.

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

Culms of Tyhpha spp. (cattails) in the Mount Vernon Trail swamp in November.

Left to right: Tyhpha latifolia at Meadowlark Botanical Gardens, Typha app. at The Mount Vernon Trail swamp (close-up and en masse).

References

Bedish JW. 1964. Studies of the germination and growth of cattail in relation to marsh management. Iowa State University, Digital Repository:
https://dr.lib.iastate.edu/entities/publication/40a81f3a-ade4-4bfb-b064-33448974ee7a

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).

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

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