Mangroves are tree and shrub communities that occupy intertidal zones of tropical and subtropical regions. The few species that compose this group display distinctive morphological, physiological and ecological traits that make them adaptable to the coastal environment dynamics (^{Hogarth, 2007}; ^{Tomlinson, 1995}). Mangroves are highly productive ecosystems, they provide several environmental services; including protection from coastal erosion, sediment trapping and they are efficient carbon sinks, also, they work as nursery and feeding areas for many fishery species (^{Sanjurjo-Rivera & Welsh-Casas, 2005}; ^{Polidoro et al., 2010}; ^{Donato et al., 2011}). In Mexico four species of mangroves are widely distributed in both the Atlantic and the Pacific coasts: Rhizophora mangle L. (Red Mangrove; Rhizophoraceae), Avicennia germinans Jacq. (Black Mangrove; Acanthaceae), Laguncularia racemosa Gaertn. (White Mangrove; Combretaceae) and Conocarpus erectus L. (Button Mangrove; Combretaceae) with two varieties (erectus and sericeus) (^{López-Portillo & Ezcurra, 2002}; ^{Pennington & Sarukhán, 2005}). Additionally, in the state of Chiapas the presence of Rhizophora harrisonii Leechman (considered a natural hybrid between R. mangle and R. racemosa G. Mey.) and Avicennia bicolor Standl. (Salty Mangrove) has been reported (^{Moldenke, 1960}; ^{Rico-Gray, 1981}; ^{Lot et al., 2015}).

Avicennia bicolor is a native mangrove of the Central American Pacific and found in the restricted areas between Buenaventura Bay in Colombia and the southern Mexican Pacific coast (^{Jiménez, 1990}, ¹⁹⁹⁴; ^{Tomlinson, 1995}; ^{Duke, 2010}). Avicennia bicolor and A. germinans can occur in mixed stands and can be easily distinguished by morphological characteristics (leaves and inflorescence arrangement) (sensu^{Gibson, 1970}; ^{Tomlinson, 1995}). Microsatellite data suggests that a contemporary genetic isolation between the two species exists (^{Nettel et al., 2008}).

The following is a dichotomous key to differentiate the two species of Avicennia present in Mexico (^{Tomlinson, 1995}).

Records of A. bicolor in Mexico are particularly scarce. Its occurrence has been cited without location data (e.g., ^{López-Portillo & Ezcurra, 2002}; ^{Rodríguez-Zúñiga et al., 2013}) or valid specimens, generating uncertainty on the actual occurrence and on its distribution in the country. The aim of this note is to report three recent records of A. bicolor in the state of Chiapas. Also, we provided data on the mangrove community structure with emphasis in A. bicolor and the general characteristics of its habitat. Additionally, information gaps of the species were determined through an analysis of its records in the Central American Pacific.

Previous records. The Japanese botanist Eizi Matuda collected the first record of A. bicolor in Mexico in 1946. This specimen collected in Paderón [sic], Chiapas (16° 2´ 25.5´´ N, 093° 51´ 59.91´´ W approximately) was deposited in the U.S. National Herbarium (US 1889845; we revised photographs of this specimen in April 10, 2015). A second specimen was collected after 40 years later, on the east of the Mar Muerto coastal lagoon (Chiapas state) during an ungraduated research project in 1987 (see section material examined) (^{Gallegos & Gómez, 1989}). The information provided by the mangrove forests inventory made on the coasts of Chiapas and Oaxaca (^{Tovilla-Hernández et al., 2007}; ²⁰¹⁰) suggests that A. bicolor is found in some sites on the northeastern of the Gulf of Tehuantepec, Mexico (Fig. 1).

Figure 1 Map of the Pacific coast of Central America showing georeferenced localities of Avicennia bicolor. Multiple records in close geographic proximity may be represented by a single symbol. Area of recent records of the species in Los Patos-Solo Dios (Chiapas, Mexico) is represented by a star. 

Recent records. Avicennia bicolor stands were in the Mangrove Priority Site Los Patos-Solo Dios, municipalities of Pijijiapan and Tonalá, Chiapas (CONABIO-PS28; ^{Rodríguez-Zúñiga et al., 2013}). In this new locality, forest structure parameters (DBH ≥ 2.5 cm, density height, basal area) were determined in three plots (300 m²) where A. bicolor was found. In April 2015 and November 2016, we collected specimens using standard field and herbarium techniques (^{Lot & Chiang, 1986}), and for botanical determination, we used the keys of ^{Gibson (1970)} and ^{Pool & Rueda (2001)}. Herbarium specimens were deposited at MEXU (National Herbarium, Universidad Nacional Autónoma de México), UAMIZ (Metropolitan Herbarium “Dr. Ramón Riba y Nava Esparza”, Universidad Autónoma Metropolitana-Iztapalapa), HEM (Herbarium “Eizi Matuda”, Universidad de Ciencias y Artes de Chiapas) and ECO-SC-H (El Colegio de la Frontera Sur-San Cristóbal).

Material examined. Mexico. Chiapas. Municipality of Tonalá: Mar Muerto, Estero Cinco Arrobas, ca. 7.5 km southeast of Paredón, 15° 51´ N, 093° 51´ W, 28 February 1987, A. Gómez and M. Gallegos, 268 (UAMIZ 32515); Panama. Province of Coclé: On Isla del Pozo in salinas (salt flats) of Rio Estero Salado, 8° 11´ N, 080° 30´ W, 12 February 1982, S. Knapp, K. Clary and D. Piperno, 3401 (MEXU 378957); Province of Panama: Punta Chame, 10-15 miles from Pan-American Highway, 8° 40´ N, 79° 45´ W, 17 September 1981, S. Knapp, 1244 (MEXU 382325).

Additional material from the new locality. Mexico. Chiapas. Municipality of Pijijiapan: Los Patos-Solo Dios lagoon system, ca. 120 m east of the San José estuary channel and 500 m north of the beach, 15° 43’ 39.50” N, 93° 29’ 50.20” W, S. Santamaría-Damián 001 and E. I. Romero-Berny, s/n (MEXU, UAMIZ. HEM, ECO-SC-H), 13 April 2015 (Fig. 2). Ca. 40 m east of the San José estuary channel and 510 m north of the beach, 15° 42’ 55.60” N, 093° 28’ 52.70” W, S. Santamaría-Damián 002 and E. I. Romero-Berny, s/n (MEXU, UAMIZ. HEM, ECO-SC-H), 15 April 2015. Municipality of Tonalá: Los Patos-Solo Dios lagoon system, ca. 50 m south of the La Ceiba fishing pier, 15° 45’ 30.66” N, 093° 31’ 48.74” W, S. Santamaría-Damián 003 and E. I. Romero-Berny, s/n (HEM, ECO-SC-H), 18 November 2016.

Figure 2 Herbarium specimen of Avicennia bicolor 

Tree community structure. In Los Patos-Solo Dios lagoon system, mean density of A. bicolor trees (DBH≥ 2.5 cm) was estimated at 234 ± 86 trees ha^-1. Average basal area and mean height were 16.1 m² ha^-1 and 13.9 m, respectively. Avicennia bicolor stands were observed in an intertidal creek adjacent to the main estuarine channel. These stands are located to the side of the sandbar that separates the estuary from the open ocean and it has a surface salinity of 34 psu (dry season, February 2010). Rhizophora mangle trees occurred at the borders of the creek (605±177 trees ha^-1) while the A. germinans stands (661±107 trees ha^-1) are surrounding the stands of A. bicolor. The composition and structure of dry climate mangroves along the Pacific of Central America show differences among stands in the inland and edge sections of the forest where the runoff seasonally modifies the patterns of local drought and salinity, which is evident in A. bicolor- A. germinans mixed stands (^{Jiménez, 1990}). In general, the communities of A. bicolor in this new Mexican locality have a more developed forest structure in comparison to those of the Gulf of Fonseca (southeastern El Salvador), where low values of density, height and basal area are reported (^{Chicas-Batres et al.,2016}).

Distribution records. To summarize the distribution records of A. bicolor in the Central American Pacific, we compiled locality data using the Global Biodiversity Information Facility dataset (^{GBIF, 2013}) and literature. The search of GBIF returned 176 records with georeferenced data (including the synonym A. tonduzii). The species has been collected in seven countries including Mexico. Most records come from Costa Rica and Panama (Fig 1). However, there are no records north of the Gulf of Fonseca and the coast of Guatemala, with exception of those mentioned for Mexico in this note.

In Mexico, this species is restricted to a coastal stretch along the Mar Muerto lagoon to the Joaquín Amaro-La Conquista dredged channel (40.3 km). The Mar Muerto record (Paredón, Chiapas) represents the northernmost locality for this species in the Eastern Pacific, although it is necessary to intensify exploration in the northern region of the Gulf of Tehuantepec to locate a more precise distribution limit. It is also advisable to carry out a more complete characterization of its habitat to determine the environmental drivers that define its distribution and structural patterns.

Federal laws protect mangrove ecosystems in Mexico; however there is a gap with respect to A. bicolor, which is not listed in the Official Mexican Standard (Norma Oficial Mexicana, NOM-059-SEMARNAT-2001), although the UICN Red List categorized it as Vulnerable (^{Duke, 2010}; ^{SEMARNAT, 2010}). Our records show that A. bicolor is distributed in a limited but important area in the northern Mesoamerica, in relatively dense stands with high structural development. The mangrove system of Los Patos-Solo Dios lacks conservation status and is threatened by changes in land use and selective logging (^{Santamaría-Damián et al., 2015}). Therefore, it is considered congruent to give legal protection to the site and necessary to include A. bicolor in the NOM-059.