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.