Heteranthera yucatana

Distribution and ecology: ― Endemic to the state of Yucatan in the MYP (Figures 1). It is restricted to a narrow fringe of very specialized habitat, found only along the northernmost edge of an ecosystem characterized by outcrops of a thick limestone slab, which is variously eroded and covered by a thin layer of organic soil, located from just a few hundred meters up to a few kilometers southward of the coast (see Carnevali et al. 2016). All collections of this taxon have been made within 2 – 4 km from the coast, and usually only a few hundred meters from the coastal lagoon, where the brackish water of the marshlands interface with the eroded limestone outcrops with rock crevices where freshwater accumulates during the rainy season, and in some parts mixes with brackish water. Additional relevant taxa occurring in these specialized habitats are the narrow endemics Zephyranthes orellanae Carnevali, R. Duno & Tapia-Muñoz (2010: 45; Amaryllidaceae), and Ipomoea sororia D. F. Austin & Tapia-Muñoz (2000: 807; Convolvulaceae); the three species (including the Heteranthera) can be found nearby but in further differentiated microniches. Ipomoea sororia and Zephyranthes orellanae occur in shallow depressions and rock crevices that become flooded during the rainy season. In contrast, Heteranthera yucatana occurs in small seasonal ponds or shallow lagoons with silty soil, where it grows along with Sesbania herbacea (Miller 1768: 3) McVaugh (1987: 695, Fabaceae), Echinodorus berteroi (Sprengel 1825: 163) Fassett (1955: 139, Alismataceae) and Marsilea vestita Hooker & Greville (1830 [1829]: 159, Marsileaceae) vel sp. aff. Additional taxa occurring there include, among others, several species of Amaranthaceae (e. g., Blutaparon vermiculare (Linnaeus 1753: 224 – 225) Mears (1982: 113 )), Portulaca pilosa Linnaeus (1753: 445; Portulacaceae), and the endemic Cuphea gaumerii Koehne (1900: 154; Lythraceae). This ecosystem, with its array of hydrophytic microniches, resides at the seaward northern edge of an association referred to as ‘‘ selva baja caducifolia con cactáceas columnares ’’ (see Olmsted et al. 1999 for characterization and Carnevali et al. 2003 for a discussion of its phytogeography). It harbors a distinctive flora along with a mosaic of vegetation types adapted to high temperatures and severe seasonal drought, including dry forests, thorny scrub, and marshes. In fact, a high number of the plant species endemic to the MYP occur there (Carnevali et al. 2010; Carnevali et al. 2021), because these patches constitute islands of dry vegetation associations surrounded by the sea to the north and more humid plant associations to the south. Conservation Status: ― Hereranthera yucatana meets criterion B 1 ab (i, ii) + B 2 ab (i, ii) of the IUCN for Endangered (EN). It is known from three localities, its extent of occurrence (EOO) is less than 100 km 2, and the area of occurrence (AOO) is 12.00 km 2 (Figure 1). The habitat of the species is highly fragmented under natural conditions and is also simultaneously being severely threatened by anthropogenic activities, particularly touristic developments and extensive cattle ranching. None of the known populations resides in an area that is under any level of protection. Additional material revised: — Heteranthera dubia: — MEXICO. Campeche: Municipio Carmen, margen del Río Palizada y Carrizales, dentro del sistema Pluvio-Lagunar del Río Palizada, approx. 18 ° 23 ’ 00 ” N, 91 ° 51 ’ 00 ” W, 24 November 1987, E. Cabrera & H. Cabrera 14920 (MEXU- 1303374); Laguna del Este, 18 ° 21 ’ 00 ” N, 91 ° 45 ’ 00 ” W, 5 m, 3 September 1987, D. Ocaña-Nava & A. Novelo 134 (IZTA, MEXU- 592733); Laguna El Vapor, 18 ° 24 ’ 00 ” N, 91 ° 49 ’ 60 ” W, D. Ocaña-Nava & A. Novelo R. 126 (MEXU- 592733); Municipio Palizada, Palizada, 18 ° 15 ’ 11.58 ” N, 92 ° 5 ’ 28.87 ” W, 25 - 28 July 1939, E. Matuda 3872 (MEXU- 80519, MICH- 1142341). Heteranthera limosa: — MEXICO. Campeche: Municipio Carmen, 3.4 km de la carretera a Champotón en rancho Nohan, 19 ° 1 ’ 17.60 ” N, 91 ° 5 ’ 41.30 ” W, 10 October 2004, J. R. Bonilla et al. 4751 (HUMO); Avenida 5 de mayo, Isla Aguada cerca de la casa ejidal, 18 ° 46 ’ 57.80 ” N, 91 ° 29 ’ 22.50 ” W, 10 October 2004, J. R. Bonilla et al. 4680 (HUMO). Quintana Roo: Municipio José María Morelos, Chichancanab, 19 ° 54 ’ 00 ” N, 88 ° 45 ’ 36 ” W, 38 m, G. F. Gaumer 1992 (MO- 205058). Yucatán: Municipio Dzilam de Bravo, San Felipe, 1 km al O de Rancho “ Xpanha-toro ”, Reserva Ecológica de Dzilam, 21 ° 32 ’ N, 88 ° 18 ’ W, 4 m, 27 September 1991, J. Tun 362 (MEXU- 910352, UADY); Municipio Hunucmá, 3 km al S de Sisal por carretera Sisal-Hunucmá, 50 m, 21 ° 8 ’ 37.27 ” N, 90 ° 0 ’ 48.91 ” W, 30 October 1984, A. Lot & A. Novelo 1400 (MEXU- 592826, MEXU- 428775, MO- 387155); 3 km al S de Sisal por la carretera Sisal-Hunucmá, 21 ° 8 ’ 38.69 ” N, 90 ° 0 ’ 44.77 ” W, 13 July 2005, J. L. Tapia M. et al. 1593 (CICY, MEXU- 1228118, MO- 2005779, NY, UCAM, XAL); 10 km antes de Sisal saliendo de Hunucmá, approx. 21 ° 5 ’ 35.83 ” N, 89 ° 58 ’ 18.58 ” W, 28 October 1984, A. Espejo et al. 1280 (UAMIZ- 10310); Municipio Celestún, 1 km al N de la carretera Kinchil-Celestún, 21.5 km antes de llegar a Celestún, 5 km después de la desviación a Chunchucmil, 20 ° 51 ’ 47.51 ” N, 90 ° 11 ’ 7.14 ” W, 21 September 2006, J. L. Tapia M. et al. 1940 (CICY, MEXU- 1385322, MO- 2005745); Municipio Cuzamá, 1 km al N de la hacienda Chunkanán, en las inmediaciones del cenote Chasinikché (“ Hormiga del árbol rojo ”), 20 ° 43 ’ 4.33 ” N, 89 ° 19 ’ 19.72 ” W, 20 September 2005, R. Balam et al. 24 (CICY, HUH, MEXU- 1398313, MO- 2005717); Municipio Progreso, 10 km S Puerto Progreso, carretera a Mérida, 21 ° 11 ’ 0.47 ” N, 89 ° 39 ’ 8.15 ” W, 25 July 1987, E. Cabrera & H. de Cabrera 13839 (MEXU- 650487); Municipio Dzemul, 2 km al S del entronque a las Ruinas de Xtampú (sic. Xcambó), approx. 21 ° 18 ’ 00 ” N, 89 ° 19 ’ 58 ” W, 8 November 2000, G. Carnevali & J. L. Tapia 6276 (CICY, F, FLAS, HUH, K, MEXU, MO- 191747, MY, NY, PORT, SEL, TEX, UADY, UAT, UCAM, UJAT, UPRRP, VEN, XAL); Municipio Izamal, Izamal, 20 ° 56 ’ 00 ” N, 89 ° 01 ’ 00 ” W, 1895, G. F. Gaumer 840 (G, MO); Municipio Tecoh, Mayapán, 20 ° 27 ’ 58.90 ” N, 89 ° 12 ’ 52.37 ” W, 10 October 1992, M. E. Magaña 2 (UADY); Municipio Mérida, carretera Mérida-Progreso, tramo San Ignacio a Progreso, 21 ° 14 ’ 00 ” N, 89 ° 39 ’ 05 ” W, 25 September 1980, V. Rico-Gray 162 (CICY); [Municipio] Dzemul, km 8 carretera San Diego Guerra-Xtampú, 21 ° 17 ’ 45 ” N, 89 ° 20 ’ 00 ” W, 13 September 1995, J. C. Trejo 516 (CICY).