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Abstract: Permineralized infructescences are described from the Cerro del Pueblo Formation, Coahuila, Mexico. Morphological and anatomical observations of 584 infructescences support the identification and reconstruction of an infructescence, with fruit [...]

* 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 (Ohmosoxylon, 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. Key words: angiosperm woods: Campanian-Maastrichtian; Coahuila; fossil wood; Mexico; Olmos Formation; Upper Cretaceous. doi: 10.3732/ajb.0900234

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 Perez-Hernandez (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. Key words: Cerro del Pueblo Formation: Coahuila; Coahuilacarpon phytolaccoides, late Campanian; Phytolaccaceae.

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 Castaneda-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. Key words: fossil flower; Mexico; Miocene; Simojovel de Allende; Swietenia.

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 helindae Calvillo-Canadell and Cevallos-Ferriz, gen. et sp. nov., is actinomorpbic 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. Key words: Cretaceous; fossil flowers; Mexico; Oligocene; Rhamnaceae.

Among the plants collected from the Pie de Vaca Formation of the Oligocene, of Tepexi de Rodriguez, Puebla, Mexico 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. Key words: Anacardiaceae, Oligocene; Pie de Vaca Formation; Puebla, Mexico.

From the Upper Cretaceous (Maastrichtian-Campanian) Huepac Chert Locality of the Tarahumara Formation, a new extinct aquatic plant of the Haloragaceae (Subclass: Rosidae), Tarahurnara sophiae Hernfindez-Castillo and Cevallos-Ferriz, is presented. It is reconstructed on the basis of both reproductive and vegetative organs preserved in chert. Its description and comparison with extant plants are based on the analysis of 350 permanent slides made with thin section and peel techniques. A mosaic of anatomical and morphological characters found in the extant Myriophyllum, Meziella, and Haloragodendron is used to characterize the new taxon. The development from flower to fruit in the fossil plant follows similar stages found in some extant species of Myriophyllum. However, a floral cup is reported for the first time in the family, and it is compared to the persistent fused sepals (terminal corona) of Meziella. This plant reconstruction increases the morphological diversity of the Haloragaceae, demonstrates the presence of a new dispersal mechanism compared with those known for the family, suggests that this lineage had originated by at least the Upper Cretaceous, and refutes the interpretation of several haloragacean Tertiary reports as representing genera of extant plants. Key words: anatomy; Haloragaceae, floral cup; Mexico; Myriophylleae; Upper Cretaceous.

The compressed basidiocarp of a fungus belonging to Geasteraceae (Lycoperdales; Gasteromycetes) was recovered from the plant-bearing Cenozoic strata of the Pie de Vaca Formation, Puebla, Mexico. The fossil specimen consists of an open exoperidium with ten triangular rays, and a central, circular endoperidium with an eccentrical ostiole and irregular surface relief. Scanning electron microscopy revealed a delicate reticulum on the surface of rays and on samples of the endoperidium. An acetolyzed fragment of the endoperidium yielded a few fungal spores, and similar spores were also obtained from an acetolyzed rock fragment adjacent to the fossil specimen. The fossil fungus exhibits the characteristics of extant earthstars; morphological comparison between the extant and the fossil earthstar and the type of spores obtained from the endoperidium of the latter indicate its affinity with Geastrum, although uncertainty in diagnostic characters preclude its assignment to a living species. The report of a complete basidiocarp of Geastrum from the Cenozoic of Puebla may contribute greatly to the knowledge about the spatial distribution and evolutionary history of Geasteraceae and Lycoperdales.

Three anatomically preserved endocarps, each with one enclosed seed, are described from the Princeton chert (Middle Eocene) Allenby Formation of British Columbia, Canada. Fruits are avoid, unicarpellate, single-seeded drupes. Endocarps are sclerotic, with one or two ridges on the dorsal side, and a distinct ventral suture that is partially open toward the fruit apex where an obturator is present. Cells along the ventral suture are oriented parallel to the surface of the suture and have thin secondary walls and dark contents. Seeds are anatropus, bitegmic, and ventrally attached to the carpel, with a ventral raphe and a dorsal vascular plexus. The outer integument in two seeds is composed of a single layer with alternating sclereids and thin-walled cells, while in the third seed only sclereids are present. The inner integument consists of a single layer of rectangular, thin-walled cells, but the inner integument becomes multilayered in the micropylar region and along the vascular plexus. These three endorcarps with enclosed seeds have a very similar anatomy. Variation in number of cell layers, and cell size and shape in each zone is similar to that seen in extant Prunus species. However, obly seven out of about 430 species of Prunus have been studies in detail. This lack of information in extant Prunus makes the recognition of species difficult at this time. The description of these rosaceous fruits shows that by the Middle Eocene several postulated 'advanced' characters in Prunoideae were already present.

Permineralized infructescences are described from the Cerro del Pueblo Formation, Coahuila, Mexico. Morphological and anatomical observations of 584 infructescences support the identification and reconstruction of an infructescence, with fruit developed as nutlets. The fruit are each surrounded by bracts, and have a persistent style and stigma. They comprise a woody exocarp composed of macrosclereids, and mesocarp and endocarp with layers of brachysclereids. The seeds are fusiform with a thin seed coat. Seeds contain a distal hollow chamber, probably involved in dispersal, and an embryo with two cotyledons with probable helobial endosperm. The fruit and seed characters of the fossil do not correspond with an extant genus or family, thus, a new genus and species is proposed, Patocarpus coahuilensis gen. et sp. nov. Cevallos-Ferriz and Vázquez-Rueda, and is interpreted to be an extinct member of Proteales. [ABSTRACT FROM AUTHOR]

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