Nichima gen. nov. (Alismataceae) based on reproductive structures from the Oligocene-Miocene of Mexico.

PREMISE: Alismataceae, a sub-cosmopolitan family with ca. 17 genera and 113 species, is a large group of aquatic plants. Compression/impressions and bioinclusions of reproductive parts in amber support the documentation of the lineage in low-latitude North America. In Mexico, fossil aquatic plants have been infrequently documented. The new reproductive structures exhibit characteristics of Alismataceae, whose fossil record is mainly documented in the northern hemisphere through of fruits and seeds. METHODS: We described and compared 150 samples of reproductive structures preserved as impressions/compressions from the Oligocene Los Ahuehuetes locality in the state of Puebla, and two bioinclusions from the Miocene amber of Simojovel de Allende in the state of Chiapas, Mexico with extinct and extant taxa. Using a parsimony analysis based on 29 floral characters of 17 extant genera of the Alismataceae, we evaluated the relationship between the fossil material and potential living relatives. RESULTS: We discovered a new genus Nichima based on a perfect, actinomorphic flower with an expanded receptacle, three persistent sepals with multiple vasculatures, delicate and caducous petals, six stamens, and a gynoecium composed of three to more superior carpels, maturing into achenes. These characteristics resemble flowers of Alismataceae. Nichima represents an extinct member of the family, with two new species described here, Nichima magalloniae L. Hern., Cevallos-Ferriz et Hernández-Damián sp. nov. and Nichima gonzalez-medranoi L. Hern., Cevallos-Ferriz et Hernández-Damián, sp. nov. Their phylogenetic position suggests affinity with a clade that includes Baldiella, Echinodorus, and Alisma. CONCLUSIONS: Reproductive structures from the Cenozoic of Mexico support the identification of a new extinct genus, Nichima, evidencing the extensive history of Alismataceae in North America's low latitudes and suggesting a southern extension of the boreotropical flora.

Integration of vessel traits, wood density, and height in angiosperm shrubs and trees.

PREMISE OF THE STUDY: Trees and shrubs tend to occupy different niches within and across ecosystems; therefore, traits related to their resource use and life history are expected to differ. Here we analyzed how growth form is related to variation in integration among vessel traits, wood density, and height. We also considered the ecological and evolutionary consequences of such differences. METHOD: In a sample of 200 woody plant species (65 shrubs and 135 trees) from Argentina, Mexico, and the United States, standardized major axis (SMA) regression, correlation analyses, and ANOVA were used to determine whether relationships among traits differed between growth forms. The influence of phylogenetic relationships was examined with a phylogenetic ANOVA and phylogenetically independent contrasts (PICs). A principal component analysis was conducted to determine whether trees and shrubs occupy different portions of multivariate trait space. KEY RESULTS: Wood density did not differ between shrubs and trees, but there were significant differences in vessel diameter, vessel density, theoretical conductivity, and as expected, height. In addition, relationships between vessel traits and wood density differed between growth forms. Trees showed coordination among vessel traits, wood density, and height, but in shrubs, wood density and vessel traits were independent. These results hold when phylogenetic relationships were considered. In the multivariate analyses, these differences translated as significantly different positions in multivariate trait space occupied by shrubs and trees. CONCLUSIONS: Differences in trait integration between growth forms suggest that evolution of growth form in some lineages might be associated with the degree of trait interrelation.

Upper Cretaceous woods from the Olmos Formation (late Campanian-early Maastrichtian), Coahuila, Mexico.

PREMISE OF THE STUDY: The Olmos Formation was part of a system of deltas that existed in the southern portion of the Western Interior of North America during the Campanian-Maastrichtian. The paleofloristic composition from the northern portions of the Epicontinental Sea is relatively well known, but less intensive exploration in the south has precluded more detailed floristic comparison across the entire latitudinal span of the Sea. The Olmos Formation flora, with more than 100 different leaf morphotypes so far recognized and several wood types, has the most diverse Cretaceous fossil plant assemblage in Mexico and represents a valuable opportunity for comparative studies. • METHODS: The fossil woods here described were collected in the Coahuila State, Mexico. The samples were studied using standard thin section technique and identified by comparison with fossil and extant material. • KEY RESULTS: We described four new genera (Olmosoxylon, cf. Lauraceae; Coahuiloxylon, ?Anacardiaceae, ?Burseraceae; Muzquizoxylon, Cornaceae; and Wheeleroxylon, Malvaceae s.l.) and three xylotypes of angiosperms. • CONCLUSIONS: Some of the genera present in the Olmos Formation such as Javelinoxylon and Metcalfeoxylon have been described from geologic units in the USA (San Juan Basin, New Mexico and Big Bend National Park, Texas), suggesting similarity in the taxonomic composition of the floras that inhabited southern portions of the western margin of the Campanian-Maastrichtian Epicontinental Sea. Other species, however, have only been reported for the Olmos Formation, indicating some degree of local floristic differentiation among the assemblages that inhabited the southern portion of the Western Interior.

Phytolaccaceae infructescence from Cerro del Pueblo Formation, Upper Cretaceous (late Campanian), Coahuila, Mexico.

The Upper Cretaceous (late Campanian) Cerro del Pueblo Formation, Coahuila, Mexico, contains a diverse group of angiosperms represented mainly by their reproductive structures. Among these, a new permineralized infructescence is recognized based on its morphological and anatomical characters. It is a multiple infructescence composed of berry fruits with six locules, each containing a single seed with a curved embryo developed from a campylotropous ovule with pendulous placentation; integumentary anatomy is similar to that of Phytolacca spp. (Phytolaccaceae). Though this new plant from Coahuila shares reproductive characters with Phytolacca, the constant number (six) of carpels per fruit and pendulous placentation strongly support the recognition of a new taxon, Coahuilacarpon phytolaccoides Cevallos-Ferriz, Estrada-Ruiz, et Pérez-Hernández (Phytolaccaceae, Caryophyllales). This new record adds to the known plant diversity of low latitude North America (northern Mexico) and demonstrates the long geologic history of the group.

Reproductive structures of Rhamnaceae from the Cerro del Pueblo (Late Cretaceous, Coahuila) and Coatzingo (Oligocene, Puebla) Formations, Mexico.

Recently discovered fossil flowers from the Cretaceous Cerro del Pueblo and flowers and fruits from the Oligocene Coatzingo Formations are assigned to the Rhamnaceae. The Cretaceous flower, Coahuilanthus belindae Calvillo-Canadell and Cevallos-Ferriz, gen. et sp. nov., is actinomorphic with fused perianth parts forming a slightly campanulate to cupulate floral cup, with sepals slightly keeled and spatulate clawed petals. The Oligocene fossils include Nahinda axamilpensis Calvillo-Canadell and Cevallos-Ferriz, gen. et sp. nov. (characterized by its campanulate bisexual flower with stamens opposite, adnate to and enfolded by petals; and with the ovary ripening into a drupe), and a winged fruit assigned to Ventilago engoto Calvillo-Canadell and Cevallos-Ferriz, sp. nov. The flowers and drupe features indicate closer affinity to Zizipheae and/or Rhamneae, while the single samaroid fruit suggests the presence of Ventilagineae. However, the unique character combination in the fossil flowers precludes placing them in extant genera. Nevertheless, the history of the family is long and can be traced back to the Campanian. A detailed phylogenetic revision of the group that uses morphological characters from both extant and fossil plants is needed to better understand the significance of these records as well as other important fossils of the family.

Swietenia (Meliaceae) flower in Late Oligocene Early Miocene amber from Simojovel de Allende, Chiapas, Mexico.

The amber of Simojovel de Allende, Chiapas, Mexico, of Late Oligocene-Early Miocene age, has yielded a new flower representing the Meliaceae. The flower of Swietenia miocenica Castañeda-Posadas & Cevallos-Ferriz sp. nov. is characterized by small size; free calyx composed of five glabrous lobes, ciliolated along the margin lobes; corolla composed of five free, contortedly inserted petals with ciliolated margins; cylindrical staminal tube ending in 10 acuminate or toothed accessories and 10 sessile anthers; and a discoid stigma divided in five lobular stigmatic glands. The morphology of S. miocenica is well represented among Meliaceae. Although the new species shares many characters with Swietenia microphylla, small differences in the length and width of petals and the length of staminal tube support its recognition as a new species. The presence of this genus demonstrates the establishment of tropical communities in southern Mexico by the early Miocene and highlights the influence of the northern hemisphere flora on the extant neotropical flora of the area.

A diverse assemblage of Anacardiaceae from Oligocene sediments, Tepexi de Rodriguez, Puebla, Mexico.

Among the plants collected from the Pie de Vaca Formation of the Oligocene, of Tepexi de Rodríguez, Puebla, México are five plants of Anacardiaceae, Haplorhus medranoensis, Rhus toxicodendron, Rhus sp., Comocladia intermedia, and Pistacia marquezii represented by their leaves and/or leaflets. The past and present diversity and geographic distribution of one of these genera, Rhus, demonstrate its capability to adapt and diversify in a wide variety of environments. Leaf architecture characters of this taxon overlap with those of other genera in the family, suggesting a high degree of phenotypic plasticity. The presence in the Pie de Vaca Formation of a type of Pistacia with leaf architecture characters similar to those of Asian plants further supports a long history of exchange between low-latitude North America and Asia. Links between low-latitude North and South America and the Caribbean are suggested by the presence of Comocladia and Haplorhus. Whereas Comocladia highlights the long history of regional endemics in the area, Haplorhus, today an endemic monotypic genus of Peru, suggests exchange mechanisms between North and South America. The morphologic characters of these taxa, and those of Pseudosmodingium (Anacardiaceae), some Rosaceae, Leguminosae, and Berberidaceae, suggest that the Pie de Vaca community was established and evolved in harsh environmental conditions. The Pie de Vaca flora thus provides significant new insights into the biogeographic relationships of the low latitude vegetation of North America.