2010 - The rediscovery

Note: The translation is an unofficial document provided for information purposes only. The official source is the original publication: https://www.lankesteriana.org/indiceGENERAL.htm

The discovery of Mexipedium xerophyticum has been regarded as one of the most remarkable discoveries of the Neotropical orchid flora in recent decades (Salazar and Hágsater, 1997). Although this species has some horticultural interest, its importance lies more in biological terms, as it has changed previously held ideas about the phylogenetic and biogeographic relationships of the subfamily Cypripedioideae (Albert, 1994; Albert & Chase, 1992; Chase, 1996; Salazar & Hágsater, 1997; Shefferson, 2007; Leitch, 2009).

The history of the discovery of this species has been documented since its original description (Soto-Arenas et al., 1990) and has been recounted on other occasions (Salazar-Chávez & Hágsater, 1997; Hágsater & Soto Arenas, 1998). Similarly, some detailed descriptions of this species have already been published (Soto-Arenas et al., 1990; Soto, 2003; Soto-Arenas & Solano-Gómez, 2007). Thus, we now know that M. xerophyticum is a paleoendemic genus, exclusive to the Los Chimalapas region in the Mexican state of Oaxaca. It should be noted that the description of its habitat was also made since the original publication of this species; however, the information on its habitat has been deformed in subsequent publications, to the point of considering Mexipedium as a desert species (Koopowitz, 2008). Other aspects of this species have also been studied, such as its cytology (Cox, 1997) or its vegetative anatomy (Sandoval et al., 2003), but due to its rarity it still has many important unknown aspects (Cox et al., 1998; Shefferson, 2007).

The cultivation of this plant has caused some impact among orchidologists and hobbyists, and several works have already been developed on this subject (Koopowitz, 1995, 2008; Pasetti, 1995; LeDoux, 1996; Reddy, 2008; Anonymous 2009a,b). Therefore, this note will focus on two of the main points of the biological value of this species: (I) its particular phylogenetic situation and its evolutionary interpretation, and (II) the habitat and conservation status of this species.

Evolution and phylogeny

Since its publication, Phragmipedium xerophyticum has changed its generic position and has also been placed in two other genera: Mexipedium and Paphiopedilum, in chronological order of the respective publications. So far, these are the only known synonyms for this species:

• Phragmipedium xerophyticum Soto Arenas, Salazar & Hágsater. Orquídea (Mexiko) 12(1):2. 1990.
• Mexipedium xerophyticum (Soto Arenas, Salazar & Hágsater) V.A. Albert & M.W. Chase, Lindleyana 7(3):174. 1992.
• Paphiopedilum xerophyticum (Soto Arenas, Salazar & Hágsater) V.A. Albert & Bórge Pett., Lindleyana 9(2):138. 1994.

Although its position in any of the three genera is feasible according to phylogenetic analyses, its placement as a distinct monotypic genus is now accepted (Pridgeon et al., 1999; Soto, 2003). It has been postulated that M. xerophyticum is a relict species that represents the only survivor of a basal clade among the conduplicate-leaved slipper orchids, with intermediate traits between the Phragmipediums that are distributed exclusively in the neotropical region and the Paphiopedilum that are typical of the old world (Salazar-Chávez & Hágsater, 1997; Sandoval et al., 2003; Soto-Arenas & SolanoGómez, 2007). The genome of Mexipedium has a size of 1C ¼ 6.73 pg, and 2n ¼ 26 chromosomes, making it very similar to Phragmipedium, which is why it is considered its sister genus (Leitch et al., 2009). Consistent with these results, based on molecular studies, Albert (1994) found that the separation between Mexipedium and Paphiopedilum dates back between 16.4 and 23 million years, so at the biogeographical level it has been considered as an example of the ancient boreotropical flora of the early Miocene (Salazar-Chávez & Hágsater, 1997; Soto-Arenas & Solano-Gómez, 2007). The presence of elements of the boreotropical flora, which relates the North American flora to the Asian flora (Tiffney, 1985a,b; Cevallos-Ferriz & González-Torres, 2005), seems to be very important in the Mexipedium habitat region (Wendt, 1989). In fact, it can be argued that in general, the orchid flora of Oaxaca consistently has several of the most basal Orchidaceae lineages in their respective phylogenetic groups (Soto & Salazar, 2004). It should be noted that the Cypripedioideae are one of the oldest groups of the Orchidaceae, and therefore the analysis of this group of plants is relevant for the understanding of the evolutionary history of a family that has an origin from 111 to 119 million years ago (Janssen & Bremer, 2004).

Habitat

Mexipedium xerophyticum has only been collected in one locality in the Chimalapas region, in the Isthmus of Tehuantepec, Oaxaca. In addition, it is only known from one particular limestone outcrop at 320 m asl. The exact locality of M. xerophyticum has been kept in the AMO Herbarium in order to avoid poaching.

Mexipediums are plants that produce fan-shaped growths from which stolons with new fans are produced, allowing some clonal expansion. However, this clonal expansion is apparently somewhat limited in the natural habitat to the existence of a microbial mat (Salazar & Hágsater, 1997). In the original search expedition for this species in 1988, only seven plant clumps were found, probably representing different genotypes (genets; Soto-Arenas et al., 1990). This number of genets was obtained considering a spatial separation between plants, but without using any molecular marker to see if they are really different genotypes or not. In that expedition a complete genet and a part of another one were extracted (Salazar & Hágsater, 1997, Hágsater & Soto Arenas, 1998). All plants known in cultivation outside Mexico have been propagated from these plants, both by vegetative propagation and from seed (LeDoux, 1996; Salazar & Hágsater, 1997; Hágsater & Soto Arenas, 1998; Soto-Arenas & Solano-Gómez, 2007).

Subsequent to their discovery, two more genets were extracted in their entirety by an amateur. So far little is known about the whereabouts of these two plants, except that they were originally taken to Minatitlán, Veracruz (Soto-Arenas & Solano-Gómez, 2007). In July 1996, in a new botanical survey in the locality, Gerardo Salazar found two new plants, so that by that date only six different genets had been counted in the wild. It should be noted that, although fruit production has been observed in the field (in 1988, 1996, 1997; Soto-Arenas & Solano-Gómez, 2007), all the plants observed are adults and apparently there is no recruitment of new individuals from sexual reproduction (Salazar & Hágsater, 1997). The Mexipedium habitat region has been explored in detail and no new localities have been detected, although their existence is not ruled out, apparently these rocky outcrops are not common at the site and much of the surrounding forest has already been transformed (Salazar & Hágsater, 1997). For these reasons, it has been considered that M. xerophyticum probably cannot maintain any viable population in the wild (Soto Arenas, 1996).

The precarious situation of M. xerophyticum became much more serious in 1998, when a fire destroyed its habitat. Since then, the locality had not been explored again to assess whether plants still survived in the wild. In August 2009 a new expedition was made to this locality, and it was found that of all the previously detected plants only one survived. This plant was severely damaged by fire and apparently has not flowered since, but is currently recovering. Mr. Heriberto Hernandez, who was one of the original collectors of this species, scoured the sites where the other plants had been found and concluded that they were gone. Together with his son, Gerobuam, we went back to explore the scree, especially in the less accessible places. Thus, in a gully with vertical walls, several more plants were located (Fig. 1). A couple of them had flowers and another one had buds (Fig. 2).