Heteranthera missouriensis C.N. Horn, 2020

Heteranthera missouriensis C.N. Horn View in CoL , sp. nov. ( Fig. 1 View FIG ).

TYPE: U.S.A. KANSAS. Reno Co.:¼ mi E, 3 mi S Medora,abundant in small pool in sandhill area, plants in shallow water or stranded, 17 Aug 1977, Brooks 13349 (HOLOTYPE: BRIT [ 399736 ]!; ISOTYPES: BRIT [ 399803 ]!, KANU!, MO!, NY! ).

Inflorescencia cum 5–13floribus pluribus exsertis supra spathum.Perianthium lavandulum usgue ad purpureum.Perianthi tubus 3–5 mm longus, perianthi lobus 3–4.5 mm longus; antherae in staminiibus lateralibus 0.5–0.8 mm longae, antherae in stamine centrali 1–1.3 mm longa.

Leaf blade rounded, apex obtuse, 2.6–4.4 cm long, 2.9–5.2 cm wide. Spathe 3.6–8.5 cm long. Inflorescence 3.7–9.5 cm long with 5–13 flowers, 0–6 of which are within the spathe; floral axis elongating such that most flowers are beyond the spathe apex. Perianth tube 3–5 mm long; perianth lobes lavender to purple, 3–4.5 mm long; lateral stamens 1–1.8 mm long, the anthers 0.5–0.8 mm long; central stamen 2–3.1 mm long, the anther 1–1.3 mm long. Seeds 0.6–0.8 mm long, 0.3–0.4 mm wide, with 9–12 wings. Chromosome number 2n = 32.

Phenology.— Flowering July to November. Inflorescences developing in one or two days. Individual flowers opening about two hours after dawn and wilting in early afternoon.

Distribution ( Figs. 2 View FIG , 3 View FIG ).—Roadside ditches, rice fields, and pond edges, 10–470 m; USA, Iowa and Nebraska south to Louisiana and Texas. Introductions have been recorded in Alabama, North Carolina and California.

Representative specimens. U.S.A. ALABAMA. Jackson Co.: wet depression in access road. Barger & Taylor HC#619 (ALNHS, AUA,UWAL, AMAL). ARKANSAS. Ashley Co.: jct two roads 1.8 mi W of jct US 165, Thomas 97132 (MO, NLU, NY, TENN, UARK). St. Francis Co.: N of Cypress Creek, Denke1207 (MEM,MSU). CALIFORNIA.Glenn Co.: W of I-5rice field of organic grower, J.Lundberg s.n. (DAV). ILLINOIS. St. Clair Co.: lakes, Eggert s.n. (GH, MO, WTU). Union Co.: IL 3, 2.3 mi S jct AL 146, Hill & Koontz 34266 (ILLS, NY, USF). KANSAS. Douglas Co.: 2 mi NE of Lawrence, McGregor 715 (KANU). Harvey Co.: 2 mi N of Burrton on Co. road then 3 mi E on dirt road, Horn 549 (AAU, EA, MO, NY, UNA). Jefferson Co.: 10 mi S of McLouth, Kansas Rockerfeller Tract, Brooks & Seiler 5250 (KANU). Lyon Co.: McKinney Marsh, 1 mi W and 2 mi S of Neosho Rapids, Hauser 3157 (KANU). Pottawatomie Co.: Plum Creek, Gates 17560 (MO). LOUISIANA. Ouachita Par.: Ouachita Wildlife Management Area near Bayou Lafourche, Thomas 101069 (MO, NLU). MISSISSIPPI. Madison Co.: Barnett Reservoir, W of Safe Harbor Marina at Pearl River Waterfowl Refuge, Rogers 8784 (GH, MO, NCU, NY, SMU, USF). MISSOURI. Bates Co. : 1.5 mi W of Papinsville, Steyermark 21282 (F, MO). Boone Co.: Mo. Dairy farm pond, ca. 8 mi W of Columbia on Hwy 40, Christian s.n. (MO). Butler Co.: rice field on N side of US 60 between rt Z and rt 581, Horn 8804 (GH, MEXU, MICH,NASC,NBYC, NY). Christian Co.: 1.5 mi NE of Lindenlure, Palmer 64386 (MO, NLU, UMO). Jackson Co.: Atherton, common in Gaffner’s Lake, Bush 443 (MO, US), Sheffield, Bush 863 (BR, US). Newton Co.: 2 mi SW of Joplin, Palmer 53019 (F, MO, UMO). St. Charles Co.: 5 mi N of St. Peters, Steyermark 8914 (MO,UMO). NORTH CAROLINA. Wake Co.: lake at William B. Umstead State Park, Horn 21352 (NBYC). TENNESSEE. Shelby Co.: Meemen-Shelby Forest State Park, Bates 410 (MEM, MSU). TEXAS. Cameron Co.: Unit 1, Laguna Atascosa National Wildlife Refuge, Fleetwood 7052 (TEX,US).

Individual plants have rounded leaves with an obtuse to slightly acute apex, a floral axis commonly almost twice as long as the spathe with 5–15 flowers such that most flowers extend beyond the spathe tip. The perianth is a dark purplish color.