Flower of Mexipedium xerophyticum
|Scientific name of the genus|
|VAAlbert & MWChase|
|Scientific name of the species|
|( Soto Arenas , Salazar & Hagsater ) VAAlbert & MWChase|
Mexipedium xerophyticum is a plant from the family of orchids (Orchidaceae). They are small plants that, including the inflorescence, reach a height of 20 to 40 centimeters. They are only known from a small range in southern Mexico, where they were discovered in 1988. Within the genus Mexipedium is Mexipedium xerophyticum the only way.
Mexipedium xerophyticum is a perennial , herbaceous plant. The growth is sympodial , the individual shoot lives about five years and completes its growth with the inflorescence. From basal lying regeneration buds drive spur , so that with time a small colony can arise.
Rhizome and root
Between the individual rungs of a is low sheets wrapped rhizome of about 20 centimeters in length (five to twelve internodes ). The roots arise at the base of the shoot, not along the rhizome. The roots are densely hairy and covered by Velamen radicum , which is several layers of cells thick. The cell walls of the Velamen are numerous perforated. The thick but perforated velamen is seen as an adaptation to dry seasons - it is supposed to prevent dehydration, but to absorb existing water quickly. The tilosomes (lignified areas at the transition between velamen and exodermis ) are spongy. The cells of the exodermis and endodermis have thick cell walls and are lignified.
The shoot is covered in two rows with about five to eight thick leathery, obliquely upward-pointing leaves . The shape is oblong-oval to linear with a length of 3.5 to twelve centimeters and a width of 1.5 to two centimeters. The leaf margin can be ciliate, otherwise the leaves are not hairy. The leaf ends with a rounded tip with a small tip. The top is green, the underside light green. The leaves have a leathery, fleshy texture and are about one millimeter thick. They are folded along the midrib, which is clearly visible on the underside of the leaf. The leaf base encloses the shoot, there is no separating tissue between the leaf base and the leaf blade.
The surface is covered with a layer of wax. The stomata sit on the underside of the leaf and are surrounded by a bulging edge of the cuticle . On the top of the leaf there are large epidermal cells with thick walls that can store water. These characteristics are adaptations to dry locations.
Microscopic elevations on the leaf surfaces and the obliquely upward-pointing leaves increase the ability to absorb diffuse or oblique incident light. Within the mesophyll , the cells of the abaxial layer, i.e. the layer facing the underside of the leaf, contain most of the chloroplasts .
The little branched inflorescence appears terminal, it bears about three to seven blooming flowers one after the other . The reddish, with red-brown hair covered inflorescence stalk is about six to 14 centimeters long. It has a knot , which is covered with an oval, blunt-ended, dark brown, hairy bract . The individual flowers are also on a pedicel made up of two internodes and a bract. The pedicel is slightly compressed laterally in cross-section, the bracts are hairy and ciliate on the edge. The ovary is also hairy and provided with three longitudinal ribs, it is single-chambered with parietal placentation .
The flower measures about 1.5 to two centimeters in diameter. The petals are white with a few pink spots. The sepals have thick brown hairs on the outside. The sepals are valvat in the bud . The upper sepal arches over the flower and has a pointed end, it can also be hairy on the inside at the base and have eyelashes on the edge. The other two sepals are completely fused together (Synsepal), only sometimes have a two-part tip, but mostly end bluntly. The lateral petals are elongated, hairless except for a few eyelashes at the base, they end pointed. The lip is shaped like a bag, the edges curved inwards. On the inside there are glandular hairs. The column bears two fertile stamens and a sterile one, which is formed into a shield-shaped staminodium . All three have short stems. The stamens contain the yellow, granular pollen in two chambers . The scar is three-lobed.
An upright, cylindrically shaped capsule fruit develops from the flower . Fruits are produced in large numbers, and small bees are assumed to be pollinators.
The number of chromosomes in Mexipedium xerophyticum is 2n = 26. One pair of chromosomes is strikingly large, about twice the size of the others. Of the 26 chromosomes, 20 are metacentric and six are telocentric . The telocentric chromosomes result in a nombre fondamental (number of chromosome arms) of x = 23.
Distribution and location
The species only inhabits a small area in the Mexican state of Oaxaca in the valley of the Río del Corte. It occurs at altitudes around 300 meters. The climate is characterized by a dry period from March to May.
In forests of pine ( Pinus ), oak ( Quercus ) and Liquidambar , the plants grow on emerging limestone karst with a thin layer of humus. The dry periods are intensified by the rapidly draining water. In contrast, there is plenty of rainfall during the growing season. The well-known location is on steep rock faces facing north or east. The vegetation there is dominated by small trees such as Plumeria rubra , Bursera simaruba and Pseudobombax ellipticum . Acanthocereus , agave , beaucarnea and yucca grow in the shrub layer . In the herb layer, Mexipedium xerophyticum is associated with Selaginella , Peperomia and the orchid Cyrtopodium paniculatum, among others .
There is only one known location, the limestone cliffs are less than one hectare in size. At the time of discovery, in 1988, seven plants were growing there, the largest consisting of around 120 individual rosettes. Young plants or seedlings were not found, although all specimens bloomed and fruited. One plant and parts of a second were taken for scientific purposes. Further cultivation and reproduction were successful, so that the species is now available in specialist nurseries.
The exact location was not mentioned in the first description , nevertheless further parts of the plant were removed by collectors. The forest in the valley under the rocks has now been cleared. In 1996 only two plants could be found, after a fire in 1998 only one. In a new search in 2009, a few more plants were found near the previously known location. In its natural habitat, the species is directly threatened with extinction.
The whole genus Phragmipedium is CITES listed -Appendix I, as well as the first as Phragmipedium xerophyticum described Mexipedium .
Systematics and botanical history
Mexipedium forms the subfamily Cypripedioideae with four other genera , all of which have in common the sac-like lip and the presence of two fertile and one sterile stamen.
The species was described by Soto , Salazar and Hagsater in 1990 as Phragmipedium , this genus also occurs in America. Until then, the genera Phragmipedium and Paphiopedilum were very easy to distinguish on the basis of the ovary: one-chambered in the Asian Paphiopedilum , three-chambered in the American Phragmipedium . The description of the new species blurred this boundary: the plants have a single-chambered ovary, which was not compatible with the previous definition of Phragmipedium . As a result, Albert and Chase established a new genus called Mexipedium in 1992 with the only species Mexipedium xerophyticum . Albert and Petterson advocated a concept in 1994 to combine all three genres in one, but this did not prevail.
Genetic studies have shown that Mexipedium xerophyticum is actually the closest related to Phragmipedium , it forms the sister group to this genus . The differences - on both a genetic and a morphological basis - are usually regarded as sufficient for classification in a separate genus.
The Central American occurrence of Mexipedium xerophyticum strengthens the thesis that the subfamily Cypripedioideae originated in this area. There are other basal taxa with presumably “original” characteristics, such as Selenipedium and Cypripedium irapeanum .
The name Mexipedium is made up of the country of origin Mexico and the Greek word τὰ πέδιλα pedilon "footwear, shoe", which refers to the shape of the lip. The other four genera of the subfamily already end in - pedium or - pedilum . The species name xerophyticum refers to a drought-tolerant xerophytic plant.
- Victor A. Albert, Mark W. Chase: Mexipedium - A New Genus of Slipper Orchid (Cypripedioideae: Orchidaceae) . In: Lindleyana . tape 7 , no. 3 , 1992, ISSN 0889-258X , pp. 172-176 .
- Alec M. Pridgeon, Phillip J. Cribb, Mark W. Chase, Finn N. Rasmussen (Eds.): Genera Orchidacearum. General Introduction, Apostasioideae, Cypripedioideae . tape 1 . Oxford University Press, New York / Oxford 1999, ISBN 0-19-850513-2 , pp. 161-164 .
- Mark W. Chase: Mexipedium xerophyticum . In: Curtis's botanical magazine . tape 13 , no. 3 , 1996, ISSN 1355-4905 , pp. 130-133 .
- Esthela Sandoval, Teresa Terrazas, Gerardo Salazar, Alejandro Vallejo, Bárbara Estrada: Anatomía vegetativa de Mexipedium xerophyticum (Soto, Salazar & Hágsater) VA Albert & MW Chase y géneros relacionados (Orchidaceae, Cypripedioideae) . In: Lankesteriana . tape 3 , no. 2 , 2003, ISSN 1409-3871 , p. 54-56 ( ucr.ac.cr ).
- Eric Hágsater: Diversidad y conservación de orquídeas de la región de Chimalapa, Oaxaca, México. (PDF; 599 kB) August 4, 1997, pp. 39–44 , accessed on January 31, 2010 .
- Eduardo A. Pérez-García: El redescubrimiento de Mexipedium xerophyticum (Soto Arenas, Salazar & Hágsater) VAAlbert & MWChase . In: Lankesteriana . tape 9 , no. 3 , 2010, p. 557-563 ( ucr.ac.cr [PDF]).
- Antony V. Cox, Alec M. Pridgeon, Victor A. Albert, Mark W. Chase: Phylogenetics of the slipper orchids (Cypripedioideae, Orchidaceae), nuclear rDNA ITS sequences . In: Plant Systematics and Evolution . tape 208 , 1997, ISSN 0378-2697 , pp. 197-223 ( uio.no [PDF]). Phylogenetics of the slipper orchids (Cypripedioideae, Orchidaceae), nuclear rDNA ITS sequences ( Memento of the original from June 3, 2006 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.