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A CPIE Notebook Project – Grasses and Sedges of Hawai‘i Page viii

Basic Characteristics of Sedge Flowers

Like grasses (see previous page), sedges have small flowers lacking showy petals. But they also lack the surrounding bracts of the grass floret termed "palea" and "lemma". Rather, a single, small bract subtends (is attached below) each flower. The seed that develops from the fertilized ovary is called an achene.

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Rushes are another category of plants—like sedges, typically associated with streams and wetlands—that superficially resemble sedges. Indeed, if you stumble upon a true rush, you are likely to asume at first glance that it is some kind of sedge. A few "rushes" are in the Family Cyperaceae, such as bulrush (Schoenoplectus spp.). However, true rushes are classified in the Family Juncaceae and only on examining the inflorescence will you be corrected in your assumption.

Rushes prefer somewhat cooler temperatures and are found in wet situations at higher elevations in the Islands. Luzula is somewhat of an exception: found typically on open slopes above 2400 ft (730 m) elevation. The culms of rushes are round in cross-section (terete) or, in a few, laterally compressed. Thus, a culm with "edges" puts your unknown back into the category of a true sedge. Unfortunately, there are sedges (and rushes in Cyperaceae) with terete or weakly angled culms, so you must rely on the structure of the flower itself.

True rushes have flowers with petals and sepals, but these are much reduced and scalelike (or "chaffy"). "Scalelike" means a thin, flat, dry membranous structure; not green. Because the sepals and petals are identical, they are called tepals. The big difference that separates grasses and sedges from rushes is the nature of their fruit. In the former, the fruit has a single seed that is relatively tightly bound to the fruit wall. In rushes, the fruit is a many-seeded capsule; essentially a little container of seeds.

Rushes in Hawai‘i comprise two genera (Juncus and Luzula) with but 8 species (Wagner, Herbst, & Sohmer, 1990; Imada, 2013). The seven species of Juncus are all naturalized species. Luzula hawaiiensis is an endemic in the Hawaiian Islands.

© 2016-17 AECOS, Inc. [FILE: Sedge_Structure.html] Page viii (About sedges)
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