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Published In: A Manual of the Botany of the Northern United States 506–507. 1848. (Manual) Name publication detail

Project Name Data (Last Modified On 7/9/2009)
Acceptance : Accepted
Project Data     (Last Modified On 7/9/2009)
Status: Native


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9. Juncus debilis A. Gray (weak rush)

Pl. 94 h, i; Map 366

Aerial stems 10–40 cm tall, erect or sprawling when in deeper water, caespitose, from short, slender rhizomes. Leaves with the auricles at the top of the sheaths 1.0–1.5 mm long, papery, rounded, the leaf blades 1–13 cm long, 0.5–1.0 mm wide, tubular and hollow, circular in cross-section, with cross-partitions at regular intervals. Basal leaf 1 or absent, the sheath sometimes lacking a leaf blade. Leaves of the aerial stems 1–3. Inflorescences narrow panicles, the branches ascending, the leaflike bract at the base usually shorter than the inflorescence. Flower clusters mostly 3–35 per inflorescence, mostly wedge-shaped, each with 2–5(–10) flowers. Flowers lacking a pair of closely subtending bracts. Perianth 1.2–2.8 mm long, the sepals about as long as the petals, linear-lanceolate, the tips acuminate. Stamens 3 per flower. Fruits 2.8–4.2 mm long, longer than the perianth, narrowly ovate to elliptic in outline, the tip acute with a small mucro, 1-locular. Seeds 0.3–0.4 mm long, 1 end with a short, dark point. June–August.

Uncommon, known only from a single site in the Ozark portion of Ripley County (eastern U.S. west to Texas and Missouri). Emergent to mostly submerged aquatic in streams; elsewhere in a variety of moist, sandy habitats.

In Missouri, plants of J. debilis are unusual for the genus in their relatively weak aerial stems, which are an adaptation to the aquatic environment. Steyermark (1963) noted that his collection produced leafy offshoots in the inflorescences, and subsequently collected samples have occasionally rooted at the nodes where aerial stems have become horizontal and in contact with the substrate, presumably following flooding.



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