Grasses, Sedges, Rushes

Botanists call grasses and other grass-like plants “graminoids”. This diverse group of plants belongs to the taxonomic class called the monocots (Monocotyledoneae) – these are flowering plants (Angiosperms) that sprout a single seed-leaf when they germinate. The leaves of graminoids are generally long and linear in form and always exhibit a parallel pattern of venation. Monocots are one of the two primary classes of the flowering plants, along with the dicots (which sprout two seed leaves and have a “reticulate” or branching venation pattern).browse graminoid button

field of Alaska cotton grass
NPS Photo / Jacob Frank

After the forbs, graminoids are the most species-rich growth-form type represented in the vascular plant flora of Denali. There are 176 species from five different plant families of graminoids known to occur in Denali National Park and Preserve, 61 of which are included in the Atlas. The sedge family contributes by far the largest number of species of any vascular plant family to the flora of Denali, including 73 species of the genus Carex (the sedges), making it is the most species–rich genus in the park.

intricate grass flowers
NPS Photo / Kira Heeschen

Graminoid plant families present in the park flora are as follows:

  • Sedge family (Cyperaceae; 91 species)
  • Grass family (Poaceae; 60 species)
  • Rush family (Juncaceae; 21 species)
  • Arrowgrass family (Juncaginaceae; 2 species)
  • Cattail family (Typhaceae; 1 species)
  • Pod grass family (Scheuchzeriaceae; 1 species)

Graminoid species are very well represented in Denali’s wetland flora. These plants often form the defining element of wetland plant communities – the familiar wet sedge meadow that lines the margins around ponds and in swampy openings within the boreal forest. Large, robust sedges such as Carex aquatilis, Carex utriculata, and Carex canescens are particularly plentiful in these wetland habitats. The graminoids are a very ecologically diverse group of plants, however, and are by no means restricted to marshy and wet sites in Denali. In fact, a diverse set of these plants, including many of the grasses and sedges (species from the families Poaceae and Cyperaceae) are found in the driest plant communities on the landscape – communities occupying steep south-facing slopes from the lowlands all the way to dry alpine ridges.

To most easily distinguish among the graminoids and determine when a plant is a grass, sedge, or rush, look to its stems. Sedge stems are generally triangular in cross-section and solid (not hollow), with the leaves in three rows. Rush stems are round and solid or pithy. Grass stems are round, jointed, often hollow, and with the leaves in two rows. Use a rhyme to help remember the distinctions between families of grass-like species: “Sedges have edges, rushes are round, and grasses have nodes where leaves are found.”

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