Persicaria barbata (L.) H. Hara and Persicaria glabra (Willd.) M. Gómez (Polygonaceae): two newly recorded species from the Yucatan Peninsula and Mexico

Two species of Persicaria (L.) Mill. are reported for the first time in the Neotropics. Persicaria glabra (Willd.) M. Gómez is reported for the first time as part of the flora of the Yucatan Peninsula, Mexico, and Persicaria barbata (L.) H. Hara is newly recorded from Mexico and the Americas. We present morphological descriptions of these two species along with figures, a distribution map, and a dichotomous key for the identification of the six species of Persicaria from the Yucatan Peninsula.


Introduction
The genus Persicaria (L.) Mill. (Polygonaceae) is the second richest in the subfamily Polygonoideae, with approximately 150 species . Persicaria was for a long time treated as Polygonum sect. Persicaria (L.) Raf., until Haroldson (1978) segregated the genus from. Subsequently, studies on the morphology of the fruit, flowers, and pollen (Hong et al. 1998;Ronse Decraene et al. 2000), as well as molecular phylogenetic studies (Kim and Donoghue 2008;Sanchez et al. 2011;Schuster et al. 2011) have supported this segregation as a distinct and phylogenetically isolated genus of Polygonum.
Persicaria species are perennials and aquatic or subaquatic (Kantachot et al. 2010). Most of them are distributed in temperate regions, but a few can reach tropical and subtropical regions. The elevation range of the genus extends from sea level to over 1000 m (Heywood et al. 2007). Villaseñor (2016) estimated that 13 species of Persicaria occur in Mexico, and in the Yucatan Peninsula, Ortiz-Díaz (1994) reported four species of Polygonum sect. Persicaria, currently transferred to Persicaria. After examination of the recent herbarium collections, we identified three specimens belonging to two species not previously recorded for the flora of the Yucatan Peninsula. Here, we present the new records of P. barbata (L.) H. Hara and P. glabra (Willd.) M. Gómez and include morphological descriptions, figures, and a distribution map. We also include a dichotomous identification key to the six Persicaria species from the Yucatan Peninsula.

Methods
The core of this work focused on herbarium specimens of the largest collections of the Yucatan peninsular flora CICY, F, MEXU, MO, NY, and UADY (acronyms according to Thiers 2021). We also reviewed the taxonomic treatments of the family Polygonaceae from the Yucatan Peninsula (Standley and Steyermark 1946;Ortiz-Díaz 1994) and taxonomic treatments of other geographic regions that included the genus Persicaria (or Polygonum sect. Persicaria) (Duke 1960;Burger 1983;Wilson 1990;Hinds and Freeman 2005;Hassannejad and Ghafarbi 2017), as well as digitized type specimens in JSTOR Global Plants (JSTOR 2021) and Tropicos.org to compare and correct changes in nomenclature, new records, and distribution patterns. To create the maps of the new records, we used the coordinates from herbarium labels (CICY, UNAM, and UADY) and the Simplemappr program (Shorthouse 2010). For the maps of the previously known records, we used the coordinates of the Tropicos.org database, JSTOR Global Plants, and the UNAM open data portal.

Discussion
Polygonum barbatum (= Persicaria barbata) is a conserved name proposed by Wilson (1998). Linnaeus described Polygonum barbatum with five diagnostic characters. However, Wilson (1998) observed that more than 20 species in the subgenus Persicaria have four of these five traits, and that only Persicaria pubescens (= Polygonum pubescens) has the five characters described by Linnaeus for P. barbatum. In addition, Wilson reviewed specimens 510.14 and 510.15 from the LINN herbarium labeled as P. barbatum and determined that they are Persicaria pubescens and Persicaria hydropiperoides, respectively. That is, the only existing original specimens of Linnaeus that refer to P. barbatum do not fit the current use of this name. The traditional species currently known as P. barbatum have longer and thicker cilia (bristles) in the ochreae than P. pubescens, which has short, thin cilia. In addition, the achenes in P. pubescens are trigonous, with three styles, while in P. barbatum the achene is biconvex with two styles (Wilson 1990). To maintain nomenclature stability, Wilson (1998) proposed the conservation of P. barbatum with a new type conserved in BM, this specimen unequivocally represents these taxa. Importantly, there is no morphological description of the new type of P. barbatum. Taxonomic studies including P. barbatum (or Persicaria barbata) are still based on the description of Linnaeus, which currently corresponds to P. pubescens (Wilson 1998). Persicaria barbata is widespread in warmer regions, from India to China and Australia, possibly spreading to the islands of the Pacific Ocean (Wilson 1990(Wilson , 1998. Until now, it was unknown from the tropical Americas. The two herbarium records of P. barbata were originally determined as Persicaria acuminata (Kunth) M. Gómez. However, the presence of bristles, instead of cilia, on the margins of the ochreae and ochreolae serve to distinguish P. barbata from P. acuminata.
Our record of P. glabra is the first from the Mexican portion of the Yucatan Peninsula. In their revision of the genus, Hinds and Freeman (2005) noted that the American plants included in P. glabra are frequently treated as distinct and named Persicaria densiflora (Meisner) Moldenke. The morphological differences between P. densiflora from America and P. glabra from Asia and the Pacific are minor. There are regional trends, but they do not seem sufficient to justify the separation into two species (Hinds and Freeman 2005). Therefore, Hinds and Freeman (2005) treated P. densiflora as a synonym of P. glabra; Persicaria portoricensis Small and Polygonum portoricense Bertero ex Small are superfluous, illegitimate names and are additional synonyms P. glabra (Hinds and Freeman 2005). It is also noteworthy that the P. glabra specimens collected in Mexico and kept in Mexican herbaria (MEXU, XAL) are determined as Persicaria portoricensis or Polygonum portoricense.
Persicaria species exhibit spotty distribution, restricted to permanent or seasonal freshwater ponds throughout the Yucatán Peninsula (Ortiz-Díaz 1994). This would explain the underrepresentation of this genus in herbarium collections. We recommend a review of the genus in Mexico, which is necessary to better know the diversity and distribution of Persicaria species in the country.