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Key to Family Juncaceae
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Unlike grasses and sedges, 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 (called an achene) that is tightly bound to the fruit wall. In rushes, the fruit is a many-seeded capsule; essentially a thin-walled 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 (non-native) species. Luzula hawaiiensis is an endemic in the Hawaiian Islands. Although neither Raulerson (2006) nor Stone (1970) list any rushes occuring on Guam, the Chicago Botanical Garden (2021) includes Guam in the U.S. distribution for the mat rush, Juncus effusus.
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[START OF RUSH KEY]
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30a
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Leaf sheaths closed, blades mostly basal and margins hairy, especially in younger plants. Capsule with three red or dark brown seeds. { In open areas in mesic forests above 2,400 ft. [HAW - END] Luzula hawaiiensis Buchenau
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30b
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Leaf sheaths open or, rarely, closed, blades present or absent; if present, without hairs. Capsule with numerous seeds (15 or more). Juncus spp. .. .
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[31] |
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31a
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(30) |
Leaves without blades. Bract below inflorescence held vertical, making terminal inflorescence appear lateral .. .
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[32] |
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31b
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Leaves with blades. Bract below inflorescence leaf-like, inflorescence terminal in fact and appearance .. .
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[33] |
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32a
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(31) |
Bracts surrounding capsule (perianth) distinctly shorter than capsule. Pith of stem not solid, interrupted. { In muddy, open areas on O‘ahu, Maui, and Hawai‘i Islands. [HAW - NAT] [OBL] Juncus polyanthemos Buchenau
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32b
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Bracts surrounding capsule as long as or longer than capsule. Pith of stem solid. { Widely distributed along streams and ponds, and in wetlands and wet areas. Japanese mat rush [HAW - NAT] [GUM - NAT] [OBL]
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33a
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(31) |
 Leaves with septa (internal cross walls). { Found on Maui and Hawai‘i Islands only .. .
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[34] |
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33b
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Leaves without septa. { More widely distributed across the Islands .. .
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[35] |
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34a
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(33) |
Stems tufted. Leaf septa complete. { Betweewn 0.2 ansd 1 m tall. Common on Maui and Hawai‘i in wet areas along roads, trails, and bogs above 3,300 ft. [HAW - NAT] [OBL]
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34b
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Stems not tufted, stems arising singly from horizontal rhizomes, although may superficially appear tufted. Leaf septa incomplete. { Between 0.2 and 0.6 m tall. Common on Maui and Hawai‘i in ponds and marshes below 5000 ft. [HAW - NAT] [FACW]Juncus ensifolius Wikstrom
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35a
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(33) |
Leaves numerous, flattened and grass-like, up to ~1 cm (3/8 in) wide. Flowers clustered on branches, each branch with two linear bracts at base, together forming a somewhat umbellate head. { Found in moist to wet disturbed places from just above sea level. [HAW - NAT] [FACW] Juncus planifolius R. Br.
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35b
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Leaves few or numerous, but narrow, under 1.5 mm (< 1/16 in) in width. Flowers distributed more or less solitary along the stem, not clustered { Found in wet areas on most of the Islands above 2,300 ft. .. .
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(36) |
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36a
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(35) |
Stems branching from the base, reddish-brown, up to 1 mm in diameter. Flowers not clustered on branches, each branch with two linear bracts at base (one much shorter than the other); flowers a substantial portion opf the biomass. { Annual herb. Toad rush [HAW - NAT] [FACW]
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36b
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Stems branched, rounded, 1-2 mm in diameter. Leaves numerous, flattened and grass-like. Flowers loosely arranged along stem branches with 2-3 membranous leaf-like bracts at base of branches. { Perennial herb. [HAW - NAT] [OBL]
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 HAW TABLE OF CONTENTS
GUM TABLE OF CONTENTS
 HAW INTRODUCTION
GUM INTRODUCTION
 AECOS, Inc.
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