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Systematics and Phytogeography |
Jardín Botánico y Herbario, Facultad de Ciencias Químicas y Biológicas, Universidad Autónoma de Guadalajara, Av. Patria 1201, Apdo. Postal 1-440, 44100 Guadalajara, Jalisco, Mexico
Received for publication December 6, 2001. Accepted for publication March 28, 2002.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: biodiversity • Coalcomán • conservation • Euphorbiaceae • extinction • George B. Hinton • Michoacán • Pedilanthus coalcomanensis • western Mexico
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Nearly 30 000 species of plants are native in Mexico (Rzedowski and Equihua, 1987
), and many are endemic (Rzedowski, 1973
). The Pacific slope of Mexico has a particularly diverse flora (Rzedowski, 1993
). The sierra of Coalcomán in Michoacán, where Pedilanthus coalcomanensis Croizat was rediscovered, is located in this highly biodiverse strip of land. This rugged and isolated mountain range has recently been granted conservation priority by the Federal Commission for Conservation and Use of Biodiversity in Mexico (CONABIO) (Arriaga-Cabrera et al., 2000
). Unfortunately, a high rate of deforestation in the Coalcomán region was noted about 60 yr ago (Hinton and Rzedowski, 1975
). Casual inspection today easily reveals that as much as 50% of the area is now pasture for cattle or is used for other agricultural endeavors. Information on the location of endemic species is urgently needed to help delimit an area for protection of what may remain. The information reported here is timely because so far no biosphere reserves exist in northwestern Michoacán. And the fact that P. coalcomanensis is not yet extinct lends support to local conservation efforts.
The Euphorbiaceae, with nearly 8000 species (Jensen, Vogel-Bauer, and Nitschke, 1994
) and a cosmopolitan distribution, is divided into five subfamilies. Of these, the Euphorbioideae include the tribe Euphorbieae, in which Pedilanthus is classified. This tribe is characterized by a unique inflorescence, the cyathium (Webster, 1994
). Pedilanthus, a genus of about 14 species, is further distinguished by having a spurred zygomorphic involucre (Dressler, 1957
).
Knowledge of the collection sites of historical specimens of P. coalcomanensis is important because it has implications for research on the itinerary followed by Hinton in this region, where he collected other specimens that are nomenclaturally critical. However, after Hinton no other collectors found P. coalcomanensis again until we rediscovered it in July 1999.
The rediscovered population of P. coalcomanensis is located in tropical deciduous forest near Tehuantepec, in Chinicuila, northwestern Michoacán. It is possible that the population we documented is the same one that Hinton found in 1941.
Based on the reduced geographic distribution of P. coalcomanensis, the high propensity for the forests in that region to be cut, and the results of the assessment of extinction risk in Mexican wild species (MER), we have concluded that this species is threatened with extinction.
The objectives of this paper are to document the rediscovery of a population of P. coalcomanensis, to provide its precise geographic location, to report the vegetation where it grows, and to estimate the species' vulnerability to extinction.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Seven fieldwork trips were conducted in Aquila, Chinicuila, and Coalcomán, in northwestern Michoacán, between May 1998 and June 2001. The plant material collected during these trips was deposited in the herbarium of the Universidad Autónoma de Guadalajara (GUADA).
To determine whether P. coalcomanensis is present in other parts of Mexico, we consulted several local herbaria (CIDIIR, CIMI, CREG, EBUM, FCME, IBUG, IEB, OAX, and XAL; herbarium abbreviations according to Holmgren, Holmgren, and Barnett, 1990
), but no additional specimens were found. We also visited various regions in the vicinity of El Naranjillo (Fig. 1) in search of this species.
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, 1989
) and a polar compensation planimeter (model KP-27 zero-setting device with optical tracer, Koizumi, Japan) to estimate the surface area where this species grows.
To determine the vulnerability of P. coalcomanensis, we applied a recently developed method for the assessment of the extinction risk in Mexican wild species (MER) (SEMARNAT, 2002
). The method entails the evaluation of the following criteria: (1) distribution range of the taxon in Mexico, (2) condition of the habitat for favoring or limiting the permanence of the taxon, (3) intrinsic biological vulnerability of the taxon, and (4) impact of human activities on the taxon. The evaluation of each criterion is then scored, and the sum of scores is compared with a scale. A taxon with a score of 12–14 is considered endangered, and one with a score of 10–11 is considered threatened. Published results of MER evaluations have legal implications in Mexico because they are currently used to propose the inclusion, exclusion, or change of status of a taxon in the lists of taxa under the legal protection of NOM-059-ECOL.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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We explored a number of sites in Sierra Naranjillo and its vicinity without success. Then in July 1999 we finally located a population near Tehuantepec, in Chinicuila, growing in tropical deciduous forest. Because the plants were vegetative, we took only a couple for cultivation in the botanic garden, where they bloomed in November that same year. We visited this population again during the winter-spring of the following two years to prepare herbarium specimens and to take photographs and field notes. The location of this population is outside what local residents know as Sierra Naranjillo, although it is adjacent. After exploring an extensive area in search of this elusive species, we believe that this population is the same one found by Hinton because we found plants growing at the same elevations (1440–1600 m) indicated on Hinton's plant labels, beside the old mule road that joined Coalcomán and Tehuantepec, next to a seasonal creek, near Los Puente [Las Fuentes] (Fig. 1) a former rest stop for travelers; the vegetation of what we take to be the type locality is taller than elsewhere, more suggestive of the "woods" referred by Hinton; there we found the largest plants of P. coalcomanensis, up to 9 m tall. (Hinton's potential type collection site is marked with an empty square in Fig. 1.) On the other hand, most of Sierra Naranjillo in the modern sense lies below the elevation where Hinton's type specimen was collected, and pine and oak forests cover most of the highest elevations in this Sierra (i.e., Canoas, Fig. 1), habitats where P. coalcomanensis has not yet been found. We believe that Hinton used the name "Sierra Naranjillo" for a broader region than currently delimited.
The application of MER methodology (Table 1) to evaluate the vulnerability of P. coalcomanensis produced the following results. (1) Distribution of the species is very restricted (score = 4) because its range is less than 5% of Mexican territory. (2) Although its habitat does not seem hostile, given the level of reproduction observed, we regard it as intermediate or limiting (score = 2), rather than favorable, because seemingly suitable habitat extends far beyond the small area where the species is restricted. Further studies are necessary to elucidate the factors that limit the distribution of this taxon. They appear to be environmental, given the altitudinal limit to the species' dispersal. (3) The intrinsic biological vulnerability of the taxon is low (score = 1), as evidenced by the high recruitment level. Pedilanthus coalcomanensis appears to reproduce well both by seed and by subterranean tubercles in situ and is easily cultivated ex situ. (4) Human activities greatly affect the species. It is cut and burned with the rest of the vegetation in areas used for crops or cattle grazing. However, it seems to benefit somewhat from occasional disturbance. Also, older trees are able to survive in rocky mounds that are of little use to farmers. We therefore gave it an intermediate impact score of 3.
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Our observations of fresh material indicated the need to reevaluate details that had not been previously available. An updated description of P. coalcomanensis is available at (http://ajbsupp.botany.org/v89).
Horticultural uses
This species has potential as an ornamental plant because of its showy scarlet bracts. However, despite the spectacular color displayed at flowering time, residents of the area where it occurs apparently do not know this taxon. Flowering is conspicuous owing to the deciduous habit of the shrubs. Furthermore, flowering and fruiting last six months, spanning the winter, when there is much demand for red flowers. No other potential uses are known.
Phenology
Presence of foliage: May to November or up to January in specimens growing in shaded spots protected by the forest canopy; flowering: November to early June; fruiting: March to early June.
Distribution
A strict endemic in Chinicuila, Michoacán, in western Mexico. It is distributed over approximately 11 km2, near the municipal limit with Coalcomán; at present it is known only from the locations cited in this report. Sierra Naranjillo, which George B. Hinton identified as the site of his collections, is located in Chinicuila (Fig. 1).
Pollination
Pedilanthus coalcomanensis appears to be pollinated by hummingbirds (Dressler, 1957
). Also, we observed that black wasps commonly pierce cyathia to rob nectar, leaving characteristic scars in the medial lobes of the spur (Fig. 2). The wasps do not serve a pollination function, as the flowers are out of their reach; but wasps may be effective pollinators of other species of Pedilanthus (Sahagun-Godinez and Lomeli-Sencion, 1997
).
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) near the ecotone with oak and pine forest, on areas with calcareous rocks. The tropical deciduous forest where this species develops appears to have relatively high humidity: there is an abundance of lichens and other epiphytes. Other species growing in the area are Agave gypsophila Gentry, Calliandra laevis Rose, Cattleya aurantiaca (Batem.) P. N. Don, Clusia salvinii Donn. Sm., Hexadesmia sessilis Reichb. f., Laelia albida Batem. ex Lindl., Lysiloma acapulcense (Kunth) Benth., Meiracyllium wendlandii Reichb. f., Neobuxbaumia sp., Nyctocereus serpentinus (Lag. et Rodr.) Britt. et Rose, Oncidium cebolleta (Jacq.) Sw., Oreopanax peltatus Linden ex Regel, Pseudobombax sp., Psidium sartorianum (Berg) Niedenzu, and Pittocaulon (Senecio) hintonii H. Rob. et Brett. Elevation: 1400–1780 m. |
DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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noted that some of Hinton's collection sites are difficult to locate on modern maps, because Hinton referred his collections to "distritos," large political subdivisions no longer used in Mexico. McVaugh also pointed out that in western Michoacán, most of Hinton's collections are referred to distrito Coalcomán, but they may actually come from one of various modern municipalities, i.e., Coalcomán, Chinicuila, Coahuayana, or Aquila (Fig. 1) an area that totals approximately 6500 km2. For this reason, McVaugh warned that the references to Coalcomán in the literature citing Hinton's collections must be considered with caution. On his herbarium labels, Hinton referred to the habitat where P. coalcomanensis grows as "woods," failing to mention the conspicuous calcareous rocks. This imprecision complicated our search, as we did not know where to look for the species. Because the rocks have razor-sharp edges and at times make access difficult, areas with many of them are little used for crops or cattle pastures.
Additionally, Hinton's collection labels stated that P. coalcomanensis is a tree 5–7 m high. However, P. coalcomanensis trees at such heights are found only in few, very rocky places and also in humid ravines. By contrast, smaller shrubby plants, 1.5–2 m high, are relatively abundant on areas that are more open and have fewer rocks and less primary vegetation. Vegetation in such areas, we were told, had been cut and burned in the past. These smaller plants represent new growth produced from tubercles or from seed that germinated during the regeneration of the vegetation, favored by the new open space.
Croizat (1943)
and Dressler (1957, p. 113) stated that the involucre of P. coalcomanensis is red, because they studied only pressed specimens. However, observations of living plants in the field and of cultivated specimens in the botanic garden showed that the cyathia are uniformly green when young, turning red in senescence.
When Dressler (1957)
wrote his revision of the genus Pedilanthus, P. coalcomanensis was known only from Sierra Naranjillo. In the 1950s this region was inaccessible and had been explored botanically only by Hinton (Hinton and Rzedowski, 1975
). Hinton collected this species at various elevations on five occasions, yet always referred them to the same location: Sierra Naranjillo. Dressler (1957, p. 114) thus concluded that when the area was better explored, additional collections would extend the species' distribution range. But the northwestern part of Michoacán has remained little explored by botanists mainly because the roads are prone to flooding and landslides and because of criminal activity in the area, including the cultivation of illegal plants, which has resulted in a large military presence. Not surprisingly, P. coalcomanensis remained uncollected until 1999, when we explored northwestern Michoacán.
Guerrero-Campanur (1985)
compiled a checklist of the flora of Aquila that grows at elevations of 0–1100 m. Aquila neighbors Chinicuila and borders the Pacific ocean. Guerrero-Campanur reported only one species of Pedilanthus, P. palmeri Millsp. (B. Guerrero C. 805, XAL!). On the basis of that report and our exploration of rocky areas in Aquila, we conclude that P. coalcomanensis is absent there. We also visited Mexican herbaria that were likely to have specimens and found none.
These findings plus the MER results lead us to believe that P. coalcomanensis is a narrow endemic species, growing only in a single small region and therefore vulnerable to extinction. We therefore propose its inclusion in the Mexican legislation (NOM-059-ECOL) with the status of threatened species. We also propose its inclusion in the Red List of Threatened Plants of the International Union for the Conservation of Nature (Walter and Gillett, 1997
).
But not only P. coalcomanensis needs protection. By the 1930s Hinton already realized the threat to forests in northwestern Michoacán and other Mexican states from nomadic agriculture (Hinton and Rzedowski, 1975
, p. 13). We emphatically agree with this observation. We have seen vast extensions of forest devastated by slash-and-burn agriculture, by unplanned forest exploitation, and by the establishment of pasture for cattle. The need for protection of and research on what remains of the old-growth forests in this isolated region is critical.
Dressler (1957)
suggests that the genus Pedilanthus may have originated on the Pacific slope of tropical Mexico, since the beginning of the Tertiary. A greater precision in the timing of this event is complicated by the absence of fossil records.
The Oaxaca region is a good candidate as the center of diversification of the genus, because it contains a high diversity of species of Pedilanthus, including some of the primitive moisture-loving arborescent ones. One such woody species is P. pulchellus Dressler, which is closely related to P. coalcomanensis (Dressler, 1957
), and grows in tropical subdeciduous forest on the Pacific slope region of Oaxaca.
Pedilanthus pulchellus and P. coalcomanensis are known from isolated populations about 800 km apart. Judging from observations of their habitat, both species appear to be adapted to relatively high humidity conditions. This, and the narrow altitudinal restriction of both species, suggests that dispersion of P. coalcomanensis or its ancestor might have required a more humid paleoclimate than modern conditions.
Graham (1973)
has presented evidence that a cooler, more humid climate was present in southern Mexico during the Miocene, which allowed the migration of temperate trees from North America to the south into Mexico as far as Chiapas. Such large vegetation changes and especially the global warming that marked the transition of the Miocene into the Pliocene created an opportunity for many tropical plants to migrate and occupy the land freed by the receding temperate vegetation.
Pedilanthus pollen, if found among Miocene-Pliocene microfossils, would indicate that this genus might have spread at this time, but the mostly zoophilous flora that grows in areas with warm climate produce small amounts of pollen, and there are a number of problems associated with its fossilization (Palacios and Rzedowski, 1993
). Not surprisingly, the few available palaeobotanical reports provide no record of Pedilanthus pollen or other materials (Rzedowski and Palacios, 1977
; Graham, 1987
; Palacios and Rzedowski, 1993
; González-Medrano, 1996
; Martínez-Hernández and Ramírez-Arriaga, 1996). However, Graham (1987)
reports pollen that he tentatively attributed to Tithymalus from upper Miocene deposits of Paraje Solo in Veracruz, which he (Graham, 1993
) later rectified as Pliocene. This report warrants further study to verify whether this pollen may be assigned to Pedilanthus or a closely related genus. In the absence of more direct information, our conclusions regarding the phytogeography of P. coalcomanensis must remain tentative.
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FOOTNOTES |
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2 Author for reprint requests (esahagun{at}uag.mx
)
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Croizat L. 1943 Pedilanthus. Notes on American Euphorbiaceae. Journal of the Washington Academy of Sciences 33: 19.
Dressler R. L. 1957 The genus Pedilanthus (Euphorbiaceae). Contributions from the Gray Herbarium of Harvard University 182: 1-188
González-Medrano F. 1996 Algunos aspectos de la evolución de la vegetación de México. Boletín de la Sociedad Botánica de México 58: 129-136
Graham A. 1973 History of the arborescent temperate element in the northern Latin American biota. In A. Graham [ed.], Vegetation and vegetational history of northern Latin America, 301–314. Elsevier, New York, New York, USA
Graham A. 1987 Tropical American Tertiary floras and paleoenvironments: Mexico, Costa Rica, and Panama. American Journal of Botany 74: 1519-1531[CrossRef][ISI]
Graham A. 1993 Historical factors and biological diversity in Mexico. In T. P. Ramamoorthy, R. Bye, A. Lot, and J. Fa [eds.], Biological diversity of Mexico, 109–127. Oxford University Press, New York, New York, USA
Guerrero-Campanur B. 1985 Reconocimiento botánico de Aquila, Michoacán (México). Bachelor's Degree thesis, Universidad Michoacana de San Nicolás de Hidalgo, Morelia, Michoacán, Mexico
Hinton J. J. Rzedowski 1975 George B. Hinton, explorador botánico en el sudoeste de Mexico. Anales de la Escuela Nacional de Ciencias Biológicas 21: 1-114
Holmgren P. K. N. H. Holmgren L. C. Barnett [eds.] 1990 Index herbariorum, part I, The herbaria of the world, 8th ed. New York Botanical Garden, Bronx, New York, USA
Jensen U. I. Vogel-Bauer M. Nitschke 1994 Leguminlike proteins and the systematics of the Euphorbiaceae. Annals of the Missouri Botanical Garden 81: 160-179[CrossRef][ISI]
Martinez-Hernández E. E. Ramírez-Arriaga 1996 Paleocorología de las angiospermas de la flora mexicana durante el Mesozoico y Terciario. Algunas evidencias palinológicas. Boletín de la Sociedad Botánica de México 58: 87-97
McVaugh R. 1972 Botanical exploration in Nueva Galicia, Mexico, from 1790 to the present time. Contributions of the University of Michigan Herbarium 9: 205-357
Mittermeier R. A. C. G. de Mittermeier 1992 La importancia de la diversidad biológica de Mexico. In J. Sarukhán and R. Dirzo [eds.], México ante los retos de la biodiversidad, 63–73. Comisión Nacional para el Conocimiento y Uso de la Biodiversidad, Mexico City, Mexico
Palacios R. J. Rzedowski 1993 Estudio palinológico de las floras fósiles del Mioceno inferior y principios del Mioceno medio de la región de Pichucalco, Chiapas, México. Acta Botánica Mexicana 24: 1-96
Rzedowski J. 1973 Geographical relationships of the flora of Mexican dry regions. In A. Graham [ed.], Vegetation and vegetational history of northern Latin America, 61–71. Elsevier, New York, New York, USA
Rzedowski J. 1983 Vegetación de México. Limusa, Mexico City, Mexico
Rzedowski J. 1993 Diversity and origins of the phanerogamic flora of Mexico. In T. P. Ramamoorthy, R. Bye, A. Lot, and J. Fa [eds.], Biological diversity of Mexico: origins and distribution, 129–144. Oxford University Press, New York, New York, USA
Rzedowski J. M. Equihua 1987 Colección atlas cultural: flora. Secretaría de Educación Pública, Instituto Nacional de Antropología e Historia and Grupo Editorial Planeta, Mexico City, Mexico
Rzedowski J. R. Palacios 1977 El bosque de Engelhardtia (Oreomunnea) mexicana en la región de La Chinantla (Oaxaca, México). Una reliqua del Cenozoico. Boletín de la Sociedad Botánica de México 36: 93-123
Sahagun-Godinez E. J. A. Lomeli-Sencion 1997 Pedilanthus diazlunanus (Euphorbiaceae): pollination by hymenopterans in a bird-pollinated genus. American Journal of Botany 84: 1584-1587[Abstract]
SEMARNAT. (Secretaría del Medio Ambiente y Recursos Naturales). 2002 Norma oficial mexicana NOM-059-ECOL-2001. Protección ambiental. Especies nativas de México de flora y fauna silvestres. Categorías de riesgo y especificaciones para su inclusión, exclusión o cambio. Lista de especies en riesgo. Anexo normativo I, método de evaluación del riesgo de extinción de las especies silvestres en México (MER). Diario oficial de la Federación
SPP (Secretaría de Programación y Presupuesto). 1988 Topographic map, 1:50 000, El Ranchito, Michoacán, E13B65, 2nd printing. SPP, Mexico City, Mexico
SPP (Secretaría de Programación y Presupuesto). 1989 Topographic map, 1:50 000, Tehuantepec, Michoacán, E13B66, 2nd printing. SPP, Mexico City, Mexico
Walter K. S. H. J. Gillett 1997 Red list of threatened plants. World Conservation Union, Gland, Switzerland
Webster G. L. 1994 Synopsis of the genera and suprageneric taxa of Euphorbiaceae. Annals of the Missouri Botanical Garden 81: 33-144[CrossRef][ISI]
This article has been cited by other articles:
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  M. E. Olson, J. A. Lomeli S, and N. I. Cacho Extinction threat in the Pedilanthus clade (Euphorbia, Euphorbiaceae), with special reference to the recently rediscovered E. conzattii (P. pulchellus) Am. J. Botany, April 1, 2005; 92(4): 634 - 641. [Abstract] [Full Text] [PDF]
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