Rosaura Grether

Recent assembly of the Cerrado, a neotropical plant diversity hotspot, by in situ evolution of adaptations to fire

The relative importance of local ecological and larger-scale historical processes in causing differences in species richness across the globe remains keenly debated. To gain insight into these questions, we investigated the assembly of plant diversity in the Cerrado in South America, the worlds most species-rich tropical savanna. Time-calibrated phylogenies suggest that Cerrado lineages started to diversify less than 10 Mya, with most lineages diversifying at 4 Mya or less, coinciding with the rise to dominance of flammable C4 grasses and expansion of the savanna biome worldwide. These plant phylogenies show that Cerrado lineages are strongly associated with adaptations to fire and have sister groups in largely fire-free nearby wet forest, seasonally dry forest, subtropical grassland, or wetland vegetation. These findings imply that the Cerrado formed in situ via recent and frequent adaptive shifts to resist fire, rather than via dispersal of lineages already adapted to fire. The location of the Cerrado surrounded by a diverse array of species-rich biomes, and the apparently modest adaptive barrier posed by fire, are likely to have contributed to its striking species richness. These findings add to growing evidence that the origins and historical assembly of species-rich biomes have been idiosyncratic, driven in large part by unique features of regional- and continental-scale geohistory and that different historical processes can lead to similar levels of modern species richness.

The evolutionary history of Mimosa (Leguminosae): toward a phylogeny of the sensitive plants.

PREMISE OF THE STUDY Large genera provide remarkable opportunities to investigate patterns of morphological evolution and historical biogeography in plants. A molecular phylogeny of the species-rich and morphologically and ecologically diverse genus Mimosa was generated to evaluate its infrageneric classification, reconstruct the evolution of a set of morphological characters, and establish the relationships of Old World species to the rest of the genus. METHODS We used trnD-trnT plastid sequences for 259 species of Mimosa (ca. 50% of the total) to reconstruct the phylogeny of the genus. Six morphological characters (petiolar nectary, inflorescence type, number of stamens, number of petals, pollen type, and seismonasty) were optimized onto the molecular tree. KEY RESULTS Mimosa was recovered as a monophyletic clade nested within the Piptadenia group and includes the former members of Schrankia, corroborating transfer of that genus to Mimosa. Although we found good support for several infrageneric groups, only one section (Mimadenia) was recovered as monophyletic. All but one of the morphological characters analyzed showed high levels of homoplasy. High levels of geographic structure were found, with species from the same area tending to group together in the phylogeny. Old World species of Mimosa form a monophyletic clade deeply nested within New World groups, indicating recent (6-10 Ma) long-distance dispersal. CONCLUSIONS Although based on a single plastid region, our results establish a preliminary phylogenetic framework for Mimosa that can be used to infer patterns of morphological evolution and relationships and which provides pointers toward a revised infrageneric classification.

Acacia: The case against moving the type to Australia

Recent studies have shown that Acacia is polyphyletic and must be split into five genera. Proposal 1584 would retypify Acacia : the type of the Australian taxon A. penninervis would be conserved over the current lectotype ( A. scorpioides ) of an African taxon. We disagree with the recommendation of the Spermatophyte Committee to endorse this proposal. Contrary to Article 14.12 of the ICBN, no detailed case against conservation was presented in Proposal 1584. We maintain that there are strong arguments against conservation, such as the large number of countries that would be affected, the economic importance of the extra-Australian species, and the economic burden placed on developing countries. Acceptance of this proposal would also violate the guidelines for conservation which clearly state that the principle of priority should prevail when conservation for one part of the world would create disadvantageous change in another part of the world.

Germination of four species of the genus Mimosa (leguminosae) in a semi-arid zone of Central Mexico

Abstract Mimosa depauperata , M. lacerata , M. similis , and M. texana var. texana are dominant leguminous shrubs in the semi-arid region of Queretaro, in central Mexico. These species grow and reproduce under conditions of disturbance; they are occasionally browsed by goats and used for firewood. The effect of temperature on germination, the longevity of the seeds in the field, and the germination potential of seeds parasitized by insects of the family Bruchidae were tested. It was found that the seeds require scarification to germination. The optimum temperature for seed germination of M. similis , M. lacerata , and M. depauperata was between 20°C and 35°C and for M. texana var. texana between 30°C and 35°C. The species germinated just as well beneath the canopy as in open areas in the field. The seeds of each species are parasitized by bruchids of the genus Acanthocelides spp., and seed infestation necessarily had a detrimental effect. The seeds in the seed bank lose their longevity at a rate of 20–73% per year. As with other legumes, Mimosa seeds have a tough seed coat, which influences germination, longevity, and susceptibility to predation by bruchids. The results form this study contribute to an understanding of the phases of germination and the longevity of the seeds of Mimosa in the seed bank in arid and semi-arid communities.

Community structure of endemic Mimosa species and environmental heterogeneity in a semi-arid Mexican valley

Abstract In this paper we analyse six communities with seven Mimosa species in the Tehuacán-Cuicatlán valley, Mexico. All species are endemic to Mexico and four are endemic to the valley. Mimosa species are found in (1) the ‘matorral xerófilo’ (arid tropical scrub): Mimosa calcicola, M. lacerata, M. luisana, M. polyantha and M. purpusii, and (2) the ‘selva baja caducifolia’ (tropical deciduous forest): M. adenantheroides, Mimosa texana var. filipes. Most of them occur in similar soil environments, while M. polyantha and M. calcicola establish in particular soil conditions and only M. luisana establishes in two different sites showing a wider range of adaptation to soil characteristics. The communities studied include 24 plant families, 51 genera and ca. 70 species (5% of the total flora estimated in the valley). Heterogeneity was found among the communities. Our results point to the replacement of ‘matorral xerófilo’ and ‘selva baja caducifolia’ by ‘matorral espinoso’ (thorny scrub). Thorny species (e.g. Acacia cochliacantha, Mimosa spp.) are becoming the dominant/codominant elements in the communities. Within the communities, Mimosa species have a significant influence on soil pH, organic matter and electrical conductivity values. These species contribute to ameliorate soil nutrient conditions (OM, Ntot, P, Ca, Mg, Na and K contents) as well as other environmental factors (e.g. temperature, shade) under their canopy in degraded plant communities and may serve as ‘resource islands’. Nomenclature: Dávila et al. (1993); for endemic Mimosa species, see Material and Methods.

Nomenclatural changes in the genus Mimosa (Fabaceae, Mimosoideae) in southern Mexico and Central America.

As a result of a taxonomic study of the genus Mimosa L. for Flora de Nicaragua, Flora Mesoamericana, and Flora de M6xico, six new combinations at the infraspecific level, two new names at the specific level, and two changes of series category at the supraspecific level, are herein proposed. These taxa occur mainly in southeastern Mexico (states of Veracruz, Tabasco, Oaxaca, Chiapas, and the Yucatan Peninsula) as well as in Central America. RESUMEN. Como uno de los resultados del estudio taxon6mico del g6nero Mimosa L. para la Flora de Nicaragua, la Flora Mesoamericana y la Flora de MLxico, se proponen seis combinaciones nuevas a nivel infraespecffico, dos nombres nuevos a nivel especifico, asf como dos cambios en la categorfa de serie a nivel supraespeciffico, para los taxa existentes principalmente en el sureste de M6xico (estados de Veracruz, Tabasco, Oaxaca, Chiapas y la Peninsula de YucatAn) asf como en Centroam6rica. The genus Mimosa is characterized by biparipinnate leaves; haplostemonous or diplostemonous flowers, these disposed in capitate or spicate inflorescences; and articulate or unarticulate legumes with persistent margins. It comprises 480 to 500 species, of which 90% are American with the rest distributed in Africa and Asia. Most of the diversity is found in the tropics as well as in arid and semiarid regions at elevations from sea level up to 2250 m. Several species grow in temperate areas at 2000-2750 m (Grether, 1978; Lewis & Elias, 1981; Barneby, 1991). A taxonomic treatment of the genus for Flora Mesoamericana included 47 species with 28 varieties (Grether, 1997). In Nicaragua, 19 (40%) of these species have been found. Mexico is considered the second distributional center of the genus after Brazil: 100 to 110 species are known to occur in the country, and about 60% of them are endemic to different regions of it (Grether & Martfnez-Bernal, 1996). According to Barneby (1991), the genus in the New World comprises five sections: Mimadenia, Habbasia, Batocaulon, Calothamnos, and Mimosa; each of these includes series. Section Mimosa has been divided into three series, and series Mimosa into 37 subseries. The aim of this paper is to formalize and validate new combinations, new names, synonymies, and lectotypifications at the series, species, and variety level to accompany the taxonomic treatment of Mimosa in Flora de Nicaragua, Flora Mesoamericana, and Flora de Maxico. 1. Series Acantholobae Barneby Series Acantholobae is characterized by shrubby or arboreous species with lanceolate-oblong, oblong, or elliptic legumes, these 1-2.5 cm wide and with entire valves; the inflorescences are capitate or spicate. The group mainly occurs in Mexico and Central America, although Mimosa acantholoba (Humboldt & Bonpland ex Willdenow) Poiret var. acantholoba extends to Ecuador and Peru. Barneby (1991) considered series Acantholobae to comprise five varieties of M. acantholoba. Within this species, he accepted variation of inflorescences from globose to subglobose capitula or spikes and variation of legumes from lanceolate-oblong to oblong or elliptic, with valves glabrous, setose, or echinate. However, he described M. seticuspis as a distinct species. Within series Acantholobae, the following new combinations are proposed: Mimosa acantholoba (Humboldt & Bonpland ex Willdenow) Poiret var. seticuspis (Barneby) R. Grether, comb. et stat. nov. Basionym: Mimosa seticuspis Barneby, Mem. New York Bot. Gard. 65: 109. 1991. TYPE: El Salvador. Depto. Santa Ana: 15 km W of Metapan on low-lying ground N of Lago de Guija, 22 Feb. 1989, C. E. Hughes 1256 (holotype, NY; isotype, MEXU). In my opinion, this taxon should be treated at the infraspecific level because of its capitate inflorescences. The main difference with Mimosa acantholoba var. acantholoba is the narrower legume, NovoN 10: 29-37. 2000. This content downloaded from 157.55.39.11 on Fri, 25 Mar 2016 08:10:01 UTC All use subject to http://about.jstor.org/terms

Mimosa tejupilcana, a New Species of series Plurijugae (Leguminosae) from the State of Me&xico, Mexico

Mimosa tejupilcana, a new species from the State of Mexico, Mexico, is described and illustrated. It is presently known only from the Municipios of Valle de Bravo, Temascaltepec, Tejupilco de Hidalgo, and Amatepec. The new species is referred to series Plurijugae and that series is placed in sect. Mimosa. A key to distinguish the new species from all other taxa in the series, as well as from the similar M. adenantheroides, is provided.

Taxonomic Significance of Leaflet Anatomy in Mimosa Series Quadrivalves (Leguminosae, Mimosoideae)

Abstract Leaflet anatomy of 14 taxa in Mimosa sect. Batocaulon, series Quadrivalves is described for the first time, using cleared leaflets and light microscopy. Members of the series have obliquely asymmetric, linear-oblong, narrowly elliptic, or narrowly oblanceolate leaflets with an eccentric primary vein. The venation pattern is brochidodromous with basal lateral veins. In nine of the 14 taxa the lateral loops become notably narrower in the distal portion (anisonerved loops). On the basis of primary vein size and width, and the nature of the loops, the taxa of the series are divided into two groups, one with isonerved loops and a notably thickened primary vein (massive) and the other with anisonerved loops and a stout or moderately thickened primary vein; the primary vein and secondary veins can be sinuate or straight. Idioblasts were observed in association with the ends of the veinlets. These are of three types: polymorphic sclereids, osteosclereids, and tracheoidal elements. Calcium oxalate prisms and druses are present in most taxa of the series. The first are associated with the vascular bundles, while druses are found in mesophyll cells. The systematic value of leaflet anatomical characters is discussed, and leaflet anatomy is found to provide significant characters for distinguishing groups and individual taxa in series Quadrivalves.

Swartzia mexicana (Fabaceae, Swartzieae), a New Species from Oaxaca, Mexico

Swartzia mexicana, a new legume species from the State of Oaxaca, Mexico, is de- scribed and illustrated. It is presently known only from the districts of Ixtlin and Tuxtepec. The new species belongs to section Swartzia, subsection Swartzia, and is assigned to series Tounateae. With- in that series, it is closely related to S. sumorum by the leaflets not prominently reticulate, the style uncinate, and the stigma truncate, as well as by the legume elliptic in shape. A key to distinguish the new species from S. sumorum and S. wurdackii is provided. RESUMEN. Se describe e ilustra Swartzia mexi- cana, una especie de leguminosas nueva para la ciencia, del estado de Oaxaca, M6xico. Hasta ahora se conoce s61o de los distritos de Ixtlin y Tuxtepec. La especie nueva corresponde a la sect. Swartzia, subsect. Swartzia y se incluye en la serie Touna- teae. Dentro de esa serie, se relaciona estrecha- mente con S. sumorum por los foliolos sin nervaci6n reticulada prominente, el estilo uncinado y el es- tigma truncado, asi como por la legumbre de forma eliptica. Se presenta una clave para distinguir a la especie nueva de S. sumorum y de S. wurdackii.

Comparative study of pollen morphology and exine ultrastructure in tetrads, octads and polyads of the genus Mimosa (Leguminosae)

ABSTRACT This is the first study of exine ultrastructure to be performed in five endemic Mexican Mimosa taxa (M. pringlei var. pringlei, M. calcicola, M. spirocarpa, M. caerulea and M. sousae), one occurring in Mexico and Central America (M. occidentalis), one widely distributed throughout the neotropics (M. setosa var. paludosa), and two in South America (M. irrigua and M. daleoides). Mimosa pollen grains are associated in polyads (12 grains), octads and tetrads. Polyads and octads in members of the basal clade of Mimosa phylogeny (sect. Mimadenia) evince the affinity of Mimosa with Piptadenia. Octads are retained in sect. Batocaulon and tetrads are evolved in this section. More recent clades (sect. Habbasia, Mimosa and Calothamnos) only show tetrads varying in size and shape. Polyads show greater variation in the exine layers, with a bistratified granular structure. Octads display a columellar-granular infratectal structure while tetrads in sect. Mimosa exhibit a less variable exine with a granular infratectal structure.