Heteranthera yucatana Carnevali, Tapia-Muñoz & J.R. Grande, 2022

Carnevali, Germán, Stefano, Rodrigo Duno De, Ramírez-Morillo, Ivón M., Grande Allende, José R., Barrios, Yeni & Tapia-Muñoz, José Luis, 2022, Heteranthera yucatana (Pontederiaceae), a new, threatened species from the Mexican Yucatan Peninsula, Phytotaxa 547 (1), pp. 20-30 : 23-26

Heteranthera yucatana Carnevali, Tapia-Muñoz & J.R. Grande , sp. nov.

Type:— Mexico. Yucatán: Municipio Dzemul, 2 km al S del entronque a las Ruinas de Xtampú (sic., Xcambó), approx. 21°18’00”N, 89°19’58”W, selva baja caducifolia con cactáceas columnares, 8 November 2000, G. Carnevali & J. L. Tapia 6262 (holotype, CICY!; isotypes, FLAS!, K!, MEXU!, MO!, SEL!, TEX!, UADY!, UJAT!, US!, VEN!). Figures 1 , 2 .

A Heteranthera species similar to H. seubertiana but its leaves are pubescent (vs. glabrous) and the flowers are smaller (perianth lobes 3.2 mm vs. 7 mm), lilac with the base white-greenish (including an upper yellowish spot), whereas in H. seubertiana the petals are yellow and instead of the basal blotch there is a dark maroon-red spot at about 1/3 of the perianth lobes length.

Herbs 4.5–11.5 cm tall(including the inflorescence),annual, hydrophytic in fresh or brackish water, partially submerged, emergent or paludal, growing at the margins of seasonal ponds or water-filled rock crevices. Roots delicate, diffuse, white and dark blue in dry specimens, not exceeding 8.0 cm long. Stems consisting of creeping, aquatic rhizomes and aerial +/- erect branches; rhizomes buried under the substrate, rooting throughout, reduced or up to 4.5 cm long, 1 mm diameter, with at least one node near the apex; branches 1–5 per plant, subtended by a hyaline prophyll with acute apex, basally truncate. internodes 0.6–1.2 cm long, glabrous. Leaves distichously-alternate, distributed along the stem, floating to emergent; leaves 3.3–9.0 × 0.3–0.6 cm, linear, sometimes wider near the apex, pubescent, pubescence mainly abaxial, consisting of more or less sparse glandular capitate hairs, ca. 0.2 mm long; sheath 0.9–1.6 × 0.3–0.6 mm, narrowly rectangular, with the apex appendiculate, basally truncate, marginally hyaline; ligule 2-parted, 2.0–3.0 mm long, with two different types of tissue, one of them like the rest of the sheath and blade, the other one hyaline like the prophyll; leaf blade 2.5–7.7 × 0.2–0.6 cm, linear, basally truncate and apically acute, with the margins entire, abaxial surface pubescent; nervation parallel, with the main nerve always prominent, but mature leaves bear two additional nerves (one by each side) also conspicuous; secondary venation tessellate. Inflorescence a terminal cincinnus, 1–3 per plant, cincinnus 1–9 flowered, 4.0–10.0 cm long; peduncle 2.0– 3.2 cm long, pubescent, the hairs as in the leaves; cincinnus bract just below the lowest flower, 0.8–1.7 × 0.4–0.6 cm, ovate, entire, basally truncate, apically acuminate, slightly retrorse, with no evident midvein; floral bracts reduced, slightly to densely glandular-pubescent, floral buds narrowly ellipsoid. Flowers slightly to shortly tubular, sessile, zygomorphic, with thinly membranous perianth lobes, basally fused; perianth tube light green, 0.4–0.5 cm long, densely pubescent, with glandular and capitate hairs, ca. 0.2 mm long; perianth lobes 5 superior and 1 inferior, lilac, lateral superior lobes and central superior lobe 3.0–3.2 × 1−1.2 mm, free portion 2.8–3.0 × 0.5 mm, narrowly elliptic, the base cuneate, white-greenish, with an upper yellowish spot, apex obtuse, slightly involute, inconspicuously pubescent, with glandular and capitate hairs, ca. 0.2 mm long; inferior lobe 3.0–3.2 × 0.8−1 mm, narrowly elliptic, base cuneate, apex obtuse, slightly convoluted; stamens 3, lateral ones ca. 1.5 mm long, filaments sigmoid, somewhat inflated, white, glabrous, anthers widely elliptic, ca. 0.2 mm long; central stamen 3–3.6 mm long, filament straight, not inflated, glabrous, anthers 1.7–2.4 × 0.4–0.6 mm, ovate to slightly sagittate, white; ovary ca. 3.5 mm long, linear, glabrous; style ca. 2.5 mm long, gently sigmoid, and the stigma capitate. Capsule ca. 5−6 × 1 mm, cylindrical, green, with the perianth lobes persistent. Seeds ca. 40, 0.5 mm long, barrel shaped (dolioliform) to subglobose, green on a brown background, with 8–10 longitudinal ribs.

Paratypes:― México. Yucatán: Municipio Progreso, approx. 3.4 km SE de la Reserva Ecológica El Corchito, 21°15’31”N, 89°36’57”W, 1 m, 15 January 2020, Y . Barrios et al. 228 ( CICY!, G!, MO!); 2 km al S del entronque a las Ruinas de Xcambó , 21°18’00”N 089°19’58”W, 5 m, 22 September 2010, G . Carnevali et al. 7564 ( CICY!, MO!); carretera Zona Arqueológica de Xcambó a Dzemul , 3 km al norte de Xcambó, 21°18’30.82”N, 89° 20’ 1.95”O, 2 m., 14 January 2021, R . Duno de Stefano & G . Carnevali 3065 ( CICY!, G!); Progreso , 11–15 August 1932, W. C . Steere 3094 (F-02479637!, NY!) .

Etymology:―The specific epithet “ yucatana ” refers both to the Yucatan Peninsula and the State of Yucatan, Mexico, from which this species is apparently endemic.

Phenology:― Heteranthera yucatana has been observed in flower from August to January during the rainy season and the beginning of the dry season. The few populations sampled thus far are apparently composed of shortlived annual plants, and it is unknown at this time whether individuals/populations of the species may survive the dry season in protected places where water collects and would allow the plants to remain for a longer period.

The floral characteristics of H. yucatana strongly suggest melitophily (cf., Faegri & van der Pijl 1979): daytime anthesis, bilateral symmetry (zygomorphic flowers), horizontal-upward orientation, and lilac or lilac-violet tepals with a nectar guide at the base. However, the reduced dimensions of the flower (i.e., ca. 3.2 mm wide), the separation of the lateral stamens, the inconspicuousness of the nectar guide and the contact between the anther of the central stamen and the stigma during anthesis, suggest that spontaneous self-pollination may be the primary means of production of fruits and seeds, as has been proposed for some congeneric species ( Horn 1985). We have not been able to detect any fragrance from the flowers, nor observed any pollinators in the field.

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 B1ab(i,ii) + B2 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) .

Figures

FIGURE 1. Distribution of the species of Heteranthera in the Mexican Yucatan peninsula: Heteranthera yucatana (blue squares), H. dubia (green squares), and H. limosa (red squares).

FIGURE 2. Heteranthera (Pontederiaceae) from the Mexican Yucatan Peninsula.A–F. H. yucatana. A-B. Calichal, natural habit. C. Plant with inflorescences and flowers. D. Inflorescence. E–F. Flower. G–H. Heteranthera limosa. G. Flowers, H. Natural habitat. (C–F. H. yucatana. G. Carnevali & J.L. Tapia 6262, based upon the type collection, CICY; G–H. Heteranthera limosa. Photos:A. José R. Grande A., C–D. Germán Carnevali. E. Débora Carnevali Ramírez. B, F, G: Claudia Ramírez Díaz.