The addition of Juncus brachycephalus to the flora of Arkansas and Missouri Primary authors:Aaron Floden and Wesley Knapp

Juncus L. (Juncaceae) is a widely distributed genus that includes approximately 315 species (Kirschner 2002). Juncus subg. Septati Buchenau in the Southeastern US includes several morphologically similar species that overlap in geographic distribution (Brooks & Clements 2000). Juncus subcaudatus (Engelm.) Coville & S.F. Blake is widely distributed in the northeastern US, down the Appalachian Mountains, and then scattered westward with an increase in population density reported in the Ozarks of Missouri and northern Arkansas (Kartesz/BONAP 2024). Engelmann (1866) did not attribute J. subcaudatus to Missouri. Steyermark (1963) published a Flora of Missouri that included a scattered distribution for J. subcaudatus in the state. Since then, the species has been included as a component of the Missouri flora without question regarding its identification or status. Tim Vogt (pers. comm. with AF) has questioned the attribution and identification of this species in the state and similar habitats in adjacent states. In comparisons to herbarium specimens from the type region of J. subcaudatus and northward, plants in the Ozarks have fewer than 10 flowers per head (typically 2–6), the branches are typically held at angles less than 45 degrees from the main culm, and occur in calcareous fens and seepages.

We have reinvestigated specimens from the Ozarks and have determined that many of these populations represent a disjunct center of distribution for Juncus brachycephalus (Engelm.) Buchenau rather than the more northern J. subcaudatus. Kartesz/BONAP (2024) also shows distribution of J. brachycephalus in adjacent Oklahoma, but specimens on SERNEC (2024) of J.brachycephalus from Oklahoma appear to be a mix of other species, none of which is J.brachycephalus. Tim Vogt and AF have examined plants in the field and have noted two distinct morphological forms in the Ozarks: one that is a large plant with reddish culm bases and diffusely branched inflorescences, and a second that is more typical for J. brachycephalus with strict inflorescence branches and greenish to pale culm bases. The former is also a larger plant that tends to sprawl and lower nodes of the culm root and behave like rhizomes. We here add J. brachycephalus to the flora of Arkansas and Missouri.

Specimens examined (explicit location information is not reported due to other rare species in the fen habitats): U.S.A. ARKANSAS. Madison Co.: 2 Sep 2009, T. Witsell 09-0397 (ANHC008044); Marion Co.: 14 Sep 2010, T. Witsell 10-0339 (ANHC008241); Sharp Co.: 15 Oct 2003, T. Witsell 03-1028 (ANHC006283); 14 Sep 2001, C. Reid 3190 (UARK050021); 14 Sep 2001, C. Reid 3190 (UARK050021); 15 Sep 2001, C. Reid 3272 (UARK051218). MISSOURI. Bollinger Co.: 26 May 1977, William L. Pflieger 593 (UMO); Iron Co.: 27 October 2021, A. E. Brant 9822 (MO); Jefferson Co.: 2 Sep 1990, George Yatskievych & Kay Yatskievych 90-373 (MO); Reynolds, 31 Jul 2023, A. E. Brant & Steve Schell 10423 (MO); 15 Sep.2023, A. E. Brant 10578 (MO); Shannon Co.: 16 Aug 1979, Leroy J. Korschgen 593 (UMO); Wayne Co.: 4 Aug 2017, A. E. Brant 8501 (MO, MNH, NY, US); 31 Aug 2017, A. E. Brant 8584 (MNH, MO, NY); 6 Sep. 2017, A. E. Brant 8630 (MICH, MNH, MO, NCU, NY); 5 Oct 2017, A. E. Brant 8688 (MO); 25 Oct 2017, A. E. Brant 8711 & A. F. O’Donnell (MO); 31 Jul 2018, A. E. Brant 8896 (MO); 31 Jul 2018, A. E. Brant 8905 (MO); 14 Sep 2018, A. E. Brant 8930 (MO); 14 Sep 2018, A. E. Brant 8937 (MO).