Figure D. Native mau‘u ‘aki‘aki (Fimbristylis cymosa) growing on a Kona coast (Hawai‘i) lava flow.
Sedges are often described as plants that resemble grasses or rushes. Indeed, the more than superficial resemblances and accompanying difficulty encountered in identifing these small-flowered plants is the main reason I have constructed this key. However, I find most of the wetland and lowland sedge species fairly easy to differentiate, perhaps because there are just fewer species of sedges compared with grasses in Hawai‘i.
Sedges have the following general characteristics: culm (the upright stem that supports the inflorescence) leafy or not, usually three-sided (trigonous), and solid (or spongy; not internally hollow as in most grasses); leaves linear and sheathing the culm, in some species reduced just to the sheath part; plants spreading by rhizomes or stolons.
Sedges and rushes are widely distributed in wet places or in water; however, many sedges occur in non-wetland environments. Another group of plants, also known as rushes (Family Juncaceae), resemble many Cyperaceae in growth form and typically also occur in wet places. The Family Juncaceae is also included in this effort.
Confirmatory identification of a sedge species usually requires consideration of 1) the small flower itself, 2) the structures supporting the flowers (spikelets; see Fig. 1), and/or 3) the achene (or seed; technically, the fruit). However, our key has been constructed to be field friendly wherever possible, avoiding the need to dissect the flower or observe the achene. Pay close attention to descriptive references to the spike and spikelets.