Agave rzedowskiana, a new species in subgenus Littaea (Agavaceae) from western Mexico

Agave rzedowskiana is described and illustrated from the states of Sinaloa and Jalisco, Mexico. This species is a member of subgenusLittaea (Tagliabue) Baker “groupStriatae” of Baker. It is compared withA. petrophila García-Mend. & E. Martínez andA. dasylirioides Jacobi & Bouché.

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Resumen  Se describe e ilustraAgave rzedowskiana de los estados de Sinaloa y Jalisco, México. La especie pertenece al subgéneroLittaea (Tagliabue) Baker “Grupo Striatae” de Baker. Se le compara conA. petrophila García-Mend. & E. Martínez yA. dasylirioides Jacobi & Bouché.

     

Cactus species turnover and diversity along a latitudinal transect in the Chihuahuan Desert Region

A standardized sampling method was used to evaluate turnover (β diversity) among cactus species assemblages along a 798 km long latitudinal megatransect across the Chihuahuan Desert Region, from north-central Mexico to southern Texas. A total of 71 cactus species were found along the megatransect, 66.2% of which appeared at low frequencies, mostly as a consequence of their highly discontinuous distribution pattern. At the scale the study was conducted, there was always species turnover among cactus assemblages. The rate of turnover among contiguous sites primarily fluctuated from low to medium, but when all site combinations were considered (contiguous and non-contiguous), medium β diversity values were predominant (β = 0.331–0.66); however, 25.4% of the site pair combinations registered high values (β = 0.661–1.0). Our results showed that turnover among cactus species assemblages in the CDR does not consist for the most part of a process of species succession in the geographic space. Instead, we concluded that the continuous spatial changes in cactus species composition are primarily explained by the commonly intermittent distribution patterns of the species, by the presence in the megatransect of species at the margin of their distribution range, and, to a lesser extent, by the existence of narrowly endemic species.     

An arsenic-tolerant new species of Eleocharis (Cyperaceae) from Chihuahua, Mexico

A new aquatic, arsenic-tolerant species ofEleocharis (Cyperaceae) endemic to Chihuahua, Mexico, is described and illustrated. It belongs toEleocharis sect.Eleogenus seriesMaculosae. A key for the species ofEleocharis sect.Eleogenus from Mexico is included.

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Resumen  Sc describe e ilustra una nueva especie deEleocharis (Cyperaceae) acuática, tolerante a altas concentraciones de arsénico, y endémica de Chihuahua, México. Forma parte de la secciónEleogenus serieMaculosae. Se incluye una clave para las especies deEleocharis sect.Eleogenus de México.

     

Vegetation ordination at the southern Chihuahuan Desert (San Luis Potosi,Mexico)

Cover data for 93 perennial plant species from fifty 1 ha sites, were used to ordinate desert vegetation in relation to 50 environmental variables at El Huizache Corridor. Cumulative variance recovered in the Bray and Curtis variance-regression ordination was substantial (80%). Community structure of desert plant communities at El Huizache Corridor may be influenced primarily by a combination of landscape and edaphic variables, which in turn may determine the distribution and abundance of moisture and nutrients, and perhaps promote habitat specialization and or competitive exclusion. Secondly, to a lesser extent, climate variables could be influencing community organization at small scale gradients, the longer the gradient the more relevant climatic factors become. First axis represented a landscape gradient; it was positively correlated to exposure, geology, slope angle, rocks, stoniness, iron, January mean temperature, and organic matter content; it was negatively correlated with latitude, longitude, soil depth, and potassium content. The second axis represented mainly a climatic gradient; it was positively correlated with mean precipitation of January, February, July, August, September, November, December, annual mean precipitation, Lang's Index, organic matter content, and stoniness. The third axis represented an edaphic gradient; it was positively correlated with electrical conductivity, Mn, Zn and elevation, and negatively correlated with pH, nitrates, Ca, and disturbance. These findings should guide conservation efforts to maintain species diversity and endemism at this area. This revised version was published online in June 2006 with corrections to the Cover Date.     

Genetic diversity of the endangered endemic Agave victoriae-reginae (Agavaceae) in the Chihuahuan Desert

Long-lived perennials are a species-rich, ecologically important component of the North American deserts, yet we know little about their genetic structure, information important for their conservation. Agave victoriae-reginae is an endemic of the Chihuahuan Desert of northern Mexico that is endangered by collection for the ornamental trade. We examined levels and patterns of variation at ten polymorphic allozyme loci in ten populations representing the range of the species. Levels of genetic variation (mean H_e= 0.335) and differentiation (mean F_ST = 0.236) were high. Phenetic clustering suggested the existence of at least three distinct groups of populations. If this pattern of variation is representative of other long-lived desert perennials, it may explain the species richness of this group and will pose a real challenge to gene conservation efforts.     

Two new species of Physalis (Solanaceae) endemic to Jalisco, Mexico

Two new species ofPhysalis, both endemic to Jalisco, Mexico, are described and illustrated:P. longiloba andP. tamayoi.

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Resumen  Se describen e ilustran dos nuevas especies dePhysalis endémicas de Jalisco, México:P. longiloba y.P. tamayoi.

     

Pattern and timing of diversification in Yucca (Agavaceae): specialized pollination does not escalate rates of diversification

The yucca-yucca moth interaction is one of the most well-known and remarkable obligate pollination mutualisms, and is an important study system for understanding coevolution. Previous research suggests that specialist pollinators can promote rapid diversification in plants, and theoretical work has predicted that obligate pollination mutualism promotes cospeciation between plants and their pollinators, resulting in contemporaneous, parallel diversification. However, a lack of information about the age of Yucca has impeded efforts to test these hypotheses. We used analyses of 4322 AFLP markers and cpDNA sequence data representing six non-protein-coding regions (trnT-trnL, trnL, trnL intron, trnL-trnF, rps16 and clpP intron 2) from all 34 species to recover a consensus organismal phylogeny, and used penalized likelihood to estimate divergence times and speciation rates in Yucca. The results indicate that the pollination mutualism did not accelerate diversification, as Yucca diversity (34 species) is not significantly greater than that of its non-moth-pollinated sister group, Agave sensu latissimus (240 species). The new phylogenetic estimates also corroborate the suggestion that the plant-moth pollination mutualism has at least two origins within the Agavaceae. Finally, age estimates show significant discord between the age of Yucca (ca 6-10Myr) and the current best estimates for the age of their pollinators (32-40Myr).     

Astragalus mario-sousae (Fabaceae: Galegeae), a new species from northeastern Mexico

Astragalus mario-sousae is described from the central part of state of Nuevo León, Mexico. It differs fromAstragalus esperanzae by its habit, peduncles, pedicels, and fruits.

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Resumen   Astragalus mario-sousae (Fabaceae: Galegeae), a new species from northeastern Mexico. Brittonia 57: 314–319. 2005.—Astragalus mario-sousae es propuesta como especie nueva. Se conoce solo de la porción central del estado mexicano de Nuevo León. Se presentan una descripción e ilustración. Difiere deAstragalus esperanzae por su hábito erecto, pedúnculos, pedicelos y frutos más cortos.

     

Aboveground net primary production dynamics in a northern Chihuahuan Desert ecosystem

Aboveground net primary production (ANPP) dynamics are a key element in the understanding of ecosystem processes. For semiarid environments, the pulse-reserve framework links ANPP to variable and unpredictable precipitation events contingent on surficial hydrology, soil moisture dynamics, biodiversity structure, trophic dynamics, and landscape context. Consequently, ANPP may be decoupled periodically from processes such as decomposition and may be subjected to complex feedbacks and thresholds at broader scales. As currently formulated, the pulse-reserve framework may not encompass the breadth of ANPP response to seasonal patterns of precipitation and heat inputs. Accordingly, we examined a 6-year (1999–2004), seasonal record of ANPP with respect to precipitation, soil moisture dynamics, and functional groups in a black grama (Bouteloua eriopoda) grassland and a creosotebush (Larrea tridentata) shrubland in the northern Chihuahuan Desert. Annual ANPP was similar in the grassland (51.1 g/m²) and shrubland (59.2 g/m²) and positively correlated with annual precipitation. ANPP differed among communities with respect to life forms and functional groups and responses to abiotic drivers. In keeping with the pulse-reserve model, ANPP in black grama grassland was dominated by warm-season C₄ grasses and subshrubs that responded to large, transient summer storms and associated soil moisture in the upper 30 cm. In contrast, ANPP in creosotebush shrubland occasionally responded to summer moisture, but the predominant pattern was slower, non-pulsed growth of cool-season C₃ shrubs during spring, in response to winter soil moisture accumulation and the breaking of cold dormancy. Overall, production in this Chihuahuan Desert ecosystem reflected a mix of warm-temperate arid land pulse dynamics during the summer monsoon and non-pulsed dynamics in spring driven by winter soil moisture accumulation similar to that of cool-temperate regions. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effects of kangaroo rat exclusion on vegetation structure and plant species diversity in the Chihuahuan Desert

Long-term (1977–90) experimental exclusion of three species of kangaroo rats from study plots in the Chihuahuan Desert resulted in significant increases in abundance of a tall annual grass (Aristida adscensionis) and a perennial bunch grass (Eragrostis lehmanniana). This change in the vegetative cover affected use of these plots by several other rodent species and by foraging birds. The mechanism producing this change probably involves a combination of decreased soil disturbance and reduced predation on large-sized seeds when kangaroo rats are absent. Species diversity of summer annual dicots was greater on plots where kangaroo rats were present, as predicted by keystone predator models. However, it is not clear whether this was caused directly by activities of the kangaroo rats or indirectly as a consequence of the increase in grass cover. No experimental effect on species diversity of winter annual dicots was detected. Our study site was located in a natural transition between desert scrub and grassland, where abiotic conditions and the effects of organisms may be particularly influential in determining the structure and composition of vegetation. Under these conditions kangaroo rats have a dramatic effect on plant cover and species composition.     

A new species of Sanicula L. (Umbelliferae/Apiaceae) endemic to Baja California, Mexico

A new species of the genusSanicula (sect.Sanicoria) endemic to the southern Sierra Juárez of Baja California, Mexico, is described and illustrated.Sanicula moranii resemblesS. deserticola andS. bipinnatifida, but has thicker basal leaves, with broader petioles and rachises, and shorter fruit prickles that are confined to the apical part of the mericarps. The taxonomic relationships of these species are discussed, along with aspects of their distribution and habitat.

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Resumen  Una neuva especie del géneroSanicula (secciónSanicoria) endémica de la Sierra Juárez de Baja California, México, es descrita e ilustrada.Sanicula moranii presenta similitud conS. deserticola yS. bipinnatifida, no obstante tiene gruesas hojas basales con pecíolos y raquis anchos, y espínulas del fruto más cortas que se distribuyen únicamente en la parte apical de los mericarpos. Además, se comentan las relaciones taxonómicas de las tres especies, así como algunos aspectos de sus distribuciones y hábitats.

     

A new species of Malaxis (Orchidaceae) from Morelos, Mexico

A new species from the Mexican state of Morelos, Malaxis lyonnetii, is described and illustrated. It is similar to M. lepanthiflora but is distinguished by its much smaller flowers, distally uncinate basal lip lobes, and entire, rounded apical lip lobe.

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Resumen  Se describe e ilustra a Malaxis lyonnetii, una nueva especie del estado mexicano de Morelos. Esta especie es similar a M. lepanthiflora, de la que se distingue por las flores mucho menores, los lóbulos basales del labelo distalmente uncinados y el lóbulo apical del labelo entero y redondeado.

     

A new species of Sicyos L. (Cucurbitaceae) from Oaxaca, Mexico

Sicyos mcvaughii, a new species from Oaxaca, is described and illustrated. It is similar to Sicyos sertuliferus Cogn., and grows in secondary tropical deciduous forest, between 20 and 630 meters.     

A new species in the Elaphoglossum petiolatum complex (Elaphoglossaceae) from Mexico

Elaphoglossum trichomidiatum is described from northeastern Mexico. The new species is a member of theE. petiolatum comples, which is widespread in tropical America, Africa, Southeast Asia, and the Pacific Islands. It is unique in the complex and in sectionLepidoglossa in bearing trichomidia on the abaxial blade surface.     

A new species of Tzeltalia (Solanaceae) from Mexico

A new species of Tzeltalia (Solanaceae) from Chiapas, Mexico is described and illustrated: Tzeltalia esenbeckii. A key and a table, distinguishing the members of the genus, are included.     

Ten new species of Tibouchina (Melastomataceae) from Mexico

Ten new species of Tibouchina (T. almedae, T. congestiflora, T. connata, T. hintonii, T. macvaughii, T. nanifolia, T. patens, T. roseotincta, T. sinaloensis, andT. thulia) are described from western Mexico. Distinguishing characteristics, phenology, distribution, and phylogenetic relationships are discussed. Illustrations of all these new species are provided.     

Three new species of Spigelia (Strychnaceae) from Mexico

During a revisionary study ofSpigelia, three new species from Mexico were discovered. Two of these new species appear to be narrow endemics, one in the state of Chiapas and one in the state of Guerrero, and the third is more widespread in Mexico and Guatemala. These new species are described, illustrated, and distinguished from other North AmericanSpigelias.     

A new species of Ponthieva (Orchidaceae, Cranichidinae) from Veracruz, Mexico

Ponthieva rinconii, a new orchid species from the foothills of the Sierra Madre Oriental in Veracruz, Mexico, is described and illustrated. It is similar in overall appearance to the wide-ranging upland speciesP. schaffneri, but differs from it in habitat preferences (tropical semi-evergreen forest at 650 m elevation), presence of a loose raceme, and three-lobed labellum with a basal cavity.