2007 - Technical data sheet

FICHA TECNICA DE MEXIPEDIUM XEROPHYTICUM

Technical data sheet for Mexipedium xerophyticum

Soto-Arenas, M.A. & Solano-Gómez, A.R.

In: Soto-Arenas, M.A. (compilador). Información actualizada sobre las especies de orquídeas del PROY-NOM-059-ECOL-2000. Instituto Chinoin A.C., Herbario de la Asociación Mexicana de Orquideología A.C. Bases de datos SNIB-CONABIO. Proyecto No. W029. México. D.F. 2007

Rupicolous [growing on rock] herb, sympodial, with clonal expansion; the sympodium is a fan of distichous leaves, joined to others by elongated rhizomes, 15-20 cm high, up to 1.0 m2. Roots simple, whitish-brown, glabrous with pubescence in the attachment zone, from the base of the fans, up to 0.8 mm thick. Rhizome conspicuous, elongate, straight, brittle, 1-2 mm thick, 3-8 cm long between continuous fans; with 5-12 scarious sheaths, brown, tubular to infundibuliform, obtuse or acute, mucronate, 6-9 mm long. Fans formed by 5-8 leaves, 3-12 cm tall, 6.5-13 cm wide. Leaves conduplicate, ligulate, apex unequal, obtuse, mucronate, carinate, coriaceous-fleshy, very stiff, light green, basal ones small, progressively larger, up to 3.5-12 cm long, 1.2-1.8 cm wide, 1 mm thick. Inflorescence terminal, peduncle with 2 internodes, a 2-branched panicle (rarely simple), hirsute, hairs multicellular, reddish brown; 6.5-13 cm, 1-1.3 mm thick; with a bract near the middle of the peduncle, conduplicate, tubular, rounded to caudate, yellowish, pubescent, 8-15 mm long; rachis abbreviated, with 3-7 successive flowers, one open at a time, ca. 12-15 mm long. Floral bracts imbricate, distichous, conduplicate, cymbiform, caudate, apex recurved, brown, hirsute, 4-5 x 5 mm. Pedicel short, rigid, hirsute, subtrigonous, 2.5-3 mm long, 0.8 mm thick. Ovary unilocular, with parietal placentation, trigonous, pubescent, pinkish, 27-28 mm long, 1.5 mm thick. Flower small, unscented, 1.3-2.5 mm tall, 1.5-2mm wide. Perianth deciduous, falling off when flower is apparently fresh, pinkish white, faintly textured. Sepals valvate, the lateral ones usually completely fused, adaxial surface smooth, abaxial pubescent, hairs septate; the dorsal sepal directed forward, elliptic, acute-subacute, mucronate, concave, 9-14 x 5-6.5 mm; synsepal descending, suborbicular, obtuse, mucronate, concave, 8-9.5 x 8.5-12 mm. Petals linear-ligulate, acute, arcuate, glabrous, ciliate near base, 11-15 x 2.5-3 mm. Labellum calceolate, subglobose, inflated, slightly sulcate along veins in orifice area, very delicate texture; outer surface smooth, inner surface conspicuously hirsute, near base, with glandular, multicellular, bright purple, very attractive hairs, towards bottom of labellum hairs markedly reduced, continuing along midline and white and apparently sparser, and aggregate; basal margins (around the exit hole) erect, somewhat reflexed and thickened; apical margin incurved; entrance hole small, ovate, ca. 2 x 3 mm; lateral lobes small, incurved, broadly triangular, subacute, without thickening at margins, nor projections (horns), nor forming hollow gibbous regions, adherent to each other ca. 3 mm, well delimiting entrance and exit orifices; labellum surface without “windows” or transparent areas; total length of labellum 10-14 mm, 6-8 mm high, 7-9 mm wide. Column short, gynoecium and androcecium fused only 1-2 mm, almost completely concealing the exit orifice. Stigma curved, descending, fleshy and massive, 4-5 mm long, 1-1.3 mm at widest part.

Androecium with 2 fertile stamens, and a petaloid staminode. Staminode conspicuously pedunculate, (ca. 1 mm) convex, broadly 3-lobed, apex subacute and rounded. Anthers 2, each situated at the end of a peduncle, ovate-triangular, somewhat cordate, acute or obtuse, ca. 1 mm long. Pollinia 2 on each anther, adherent to each other forming an oval, oblique structure, granular, yellowish, 0.5 x 0.4 mm.

Distribution

Current
MEXICO, OAXACA, SANTA MARIA CHIMALAPA
Mexipedium is a monotypic, endemic genus known only from the Atlantic side of the Gulf of Mexico, in the Isthmus of Tehuantepec, in the Chimalapa region.

It is only known from a single site. Salazar searched the area carefully in 1996 and 1997, but was unable to locate any other populations. The locals are not aware of any other areas with similar habitats. However, given the size of the region, it cannot be ruled out that other populations exist that have not yet been discovered. Even if new occurrences are discovered, the species' habitat is so specific and limited that the possibility of classifying the species in another endangerment category is very low. The exact location of the population is managed in the AMO's herbarium and is not accessible to the public.

Environmental conditions

Macroclimate

There is no precise climatic information for the area, due to the absence of meteorological stations. The National Atlas of the Physical Environment reports for the area a warm-humid climate with abundant rainfall in summer and percentage of winter rainfall > 10.2%, Am(f). Extrapolating from similar regions it can be assumed that the mean annual temperature should be around 25°C. T. Wendt (pers. comm.) estimates that precipitation in the Rio del Corte basin should be close to 2500 mm. The region is subject to a well-defined dry period from March to May.

Habitat

The habitat of M. xerophyticum is a rocky, karstic outcrop in the Río del Corte canyon, less than 2 ha in size. This habitat is very sparse and the absence of soil determines the existence of open areas with xerophytic vegetation consisting of stunted trees of Pseudobombax ellipticum, Bursera simaruba, Plumeria rubra, Beaucarnea sp., and Yucca elephantipes, as well as Agave, Acanthocereus, Selaginella, Pitcairnia, and Cyrtopodium macrobulbon. At least one species of Agave and Beucarnea appear to be endemic as well.

The plants are located on vertical rock walls facing north and east, so they do not receive direct sunlight for long periods. However, they are exposed to intense light and wind. Some plants have been found in humus accumulations with Selaginella specimens; others at first glance appear to grow directly on the rock, but closer examination reveals that the roots are immersed in a thin organic layer consisting mainly of a community of cyanobacteria including Nostoc, Gloeocapsa, Scytonema and Lyngbya as well as fungal hyphae (J.L. Godínez, pers. comm., 1996). The moss Pseudosymblepharis schimperiana and an undetermined species of Peperomia are also frequently found.

Current status of the habitat with respect to the needs of the species.

The particular habitat of M. xerophyticum is well preserved, however there is human disturbance around it. Most of the forest that was originally in the river valley below the limestone outcrops has been removed for pasture and a banana plot has been established less than 50 m from the scree edge. The part of the outcrop bordering the plot was invaded by vines and other weeds.

Site

Because it is an endangered species, this information is not available to the general public. It is kept in the AMO Herbarium.

Type of vegetation

Mexipedium xerophyticum grows in a sparse rocky microhabitat surrounded by a diverse mosaic of vegetation that includes high evergreen forest and tropical oak groves of Quercus oleoides, Q. conspersa and Liquidambar macrophylla. In high evergreen forest are abundant Dialium guianense, Sloanea tuerckheimii, S. meianthera, Tapirira chimalapana, Terminalia amazonia, Eleagia uxpanapensis, Calophyllum brasiliense var. rekoi, Pera barbellata, Hyeronima oblonga, Brosimim guianense and Hirtella triandra subsp. media.

Natural history of the species

Background information on the status of the species or major populations.

Mexipedium xerophyticum is one of the most interesting discoveries in orchidology in recent years. It is a biogeographic relict, which changed the perception of the phylogenetic and biogeographic relationships of the subfamily Cypripedioideae (Albert, 1994; Albert und Chase, 1992; Chase, 1996).

This species is one of the rarest and most interesting orchids in the world and is known from a population that originally had only 7 clones.

Way of life

Perennial herb, iteroparous, long-lived, rupicolous, with sympodial growth. One of the most distinctive characteristics of this species is the distinct clonal structure of the plant, consisting of a series of determinate modules (“fans”) connected by long, slender rhizomes. The plants branch frequently and usually the old parts (5 years or more) die off, which causes the new parts to acquire their physical and physiological independence, constituting separate ramets. The largest clone (“genet”) found consisted of approximately 120 fans on about 6 growth fronts, occupying an area of ca. 0.5 m2. The plant appears to explore the microhabitat via the rhizomes, and those growths that exit the microhabitat onto unsuitable rocky sites frequently die (Cox et al., 1997).

Floral biology. The plants are not self-pollinating, but fruits have been observed in all years of visits (1988, 1996, 1997). The flowers offer no reward to their pollinators and must operate a mechanism of pollination by deception. During the collection of the type specimen a pair of small wasps was observed approaching a flower, but it is not known whether they are the pollinators or not. The floral morphology suggests that small hymenopterans must be the pollinators of Mexipedium.

The flowers are self-compatible but it is not easy to obtain seeds. As in other species of the genus germination is slow and seedlings are difficult to establish once out of the jar.

Species relevance

This species is unknown to the local population. However, this genus is extremely interesting from the biological point of view and its discovery has confirmed some hypotheses about the origin of the Mexican tropical flora. Mexipedium xerophyticum is the only living representative of a basal clade with respect to other conduplicate-leaved American slipper orchids and is most likely a relic of the ancient boreotropical flora dating back to the Miocene (Albert, 1994; Wendt, 1989). It is interesting to note that a span of 4 years (1990-1994) this plant has been placed in three different genera (Phragmipedium, Mexipedium, and Paphiopedilum). Although its position in any of the three genera is congruent with the phylogeny, its placement as a distinct monotypic genus is now widely accepted (Pridgeon et al., 2000).

On the other hand, since the original description of the species, a surprisingly high number of articles have been published on this species, reflecting the great interest in the plant from a scientific point of view as a horticulturalist (Chase, 1996; Salazar und Hágsater, 1997; Koopowitz, 1995; Le Doux, 1996; Pasetti, 1995).

Population size

In 1988 seven clones of this species were located; since then it appears that two more clones have been completely removed by collectors (H. Hernández, pers. comm.). In 1996 two new clones were located at the same locality. All specimens seen are adult, apparently very old plants that appear to have survived by clonal expansion. There is no recruitment of new specimens.

Formation of new individuals

There is no recruitment of new specimens.

Phenology

Flowering has been recorded in the field in September but may extend over a longer period of the rainy season. In cultivation it has been seen in flower until November. Vegetative growth is most active during the summer. Careful observations on its vegetative growth have not been made, but individual growths appear to mature in a single year, unlike other conduplicate-leaved slipper orchids that require 2-3 years to produce flowers.

Asexual reproductive systems

All specimens seen are apparently very old adult plants that appear to have survived by clonal expansion.

Pollination

The plants are not self-pollinating, but fruits have been observed in all the years that visits have been made (1988, 1996, 1997).

Flowering

Flowering has been recorded in the field in September but may extend over a longer period of the rainy season. In cultivation it has been seen in flower until November.

Categories and risk factors

Usage

Not known. It has horticultural importance.

Conservation

The relic-like nature of Mexipedium xerophyticum suggests that it is a taxon that is near the end of a natural extinction process, which may be abruptly accelerated by human influence.

The permanence and in situ conservation of Mexipedium is still possible. Long-term permanence of the in situ population will probably require the reintroduction of artificially produced plants from seed into the habitat, once habitat protection can be assured and basic studies of the ecology of this species have been carried out that give at least some chance of success to that effort.

Removal of individuals for any purpose (including scientific research) should be avoided at all costs unless there is irrefutable evidence that the plant will be destroyed if it remains in place. Material for propagation and research may be obtained from plants currently in cultivation or through commercial growers in the United States.

It should be taken into account that their horticultural interest and the price that a plant can fetch on the black market is so high that they seriously endanger wild individuals.

From the beginning we realized that it was very important to start an ex situ conservation program of this orchid. For this purpose, some segments of 2 clones were collected for distribution among expert growers of this group of plants. These two plants are still in cultivation at the Rio Verde Nursery in Temascaltepec, Edo. de Mexico, where they have been propagated vegetatively. A small division of these two clones was sent to Dr. Lucille McCook of the Smithsonian Institution, Washington, D.C., when she was doing research on the systematics of the genus Phragmipedium. From these divisions, Marilyn LeDoux, an expert horticulturist in charge of the orchid collection at the Saint Louis Botanical Garden, Missouri, developed a successful cultivation method that allowed the plants to flower regularly and to obtain seeds that were propagated by asymbiotic techniques in the United States, where they have been commercially available since 1994 (LeDoux, 1996).

Although Mexipedium plants were initially quite difficult to maintain in Mexico, over the years skills have been developed to grow them in cultivation and it can be said that they are not especially difficult to cultivate by trained horticulturists under appropriate warm greenhouse conditions. Horticultural information on Mexipedium can be obtained from Ledoux, 1994; Koopowitz, 1995.

Salazar and Hágsater (1997) propose the implementation of several actions for the conservation of this species, which can be summarized as follows:

Protection of karst outcrops on the southern crest of the Rio del Corte, if possible by establishing a “sanctuary” under the terms established in the General Law of Ecological Equilibrium.
Evaluation of the current status of the population and collection of information on critical aspects of reproductive biology and life history, especially if reintroduction is considered.
Establishment of an ex situ conservation program, including artificial propagation and maintenance and increase of genetic diversity.

Risk Factors

The extreme demographic rarity of this species, its high habitat specificity, small habitat area, and life history characteristics make it extremely vulnerable.

Additionally, it belongs to the most widely cultivated group of orchids, the subfamily Cypripedioideae, and is highly desirable from a horticultural point of view.

The only known population of the genus Mexipedium is in imminent danger of disappearing as a result of the modification or total destruction of its habitat, being urgent to carry out actions to ensure its permanence.

CITES: Appendix I

NOM-059-SEMARNAT-2001: P threatened with extinction

IUCN: NE Not evaluated

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