Tropical Bryology, Volume 6 (1992)
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Botanical history has recorded significant contributions of bryology to its conceptual development and to man’s scientific knowledge. The discovery of sexual chromosomes in plants by Allen and the production of the first polyploids by Wettstein are but two scientific achievments in which bryophytes had an outstanding role. Currently, their use in environmental monitoring and the identification of active principles, make bryophytes objects of great pragmatic interest.
214 Lichen and 38 bryophyte species are reported from Cerro Guaiquinima, a sandstone table mountain in southeastern Venezuela, thus fas almost unexplored for these groups and apparently undisturbed by man. Slightly over half of these species have also been reported from the north slope of Mount Roraima and surroundings, a nearby area with similar edaphic and climatological conditions.
The pleurocarpous moss genus Isopterygium (Hypnaceae) is revised for Latin America. Although as many as 92 species and varieties have been reported for the region over past years, these are currently accommodated by the present revision into only eight species. The most common taxon throughout most of Latin America, Isopterygium tenerum (Sw.) Mitt, is also the most polymorphic and presently 45 taxa are recognized as synonyms. The other seven species are I. affusum Mitt., I. acutifolium Irel., I. byssobolax Par., I. jamaicense Buck Broth., I. subglobosum Herz., and I. tenerifolium Mitt.+
References are made to cytotoxic and/or antitumor compounds that have been isolated - ansamitocin P-3 from Claopodium crispifolium (Hook.) Ren. & Card. and Anomodon attenuatus Hueb., or an associated actinomycete, and ohioensins and pallidisetums from Polytrichum spp. Several hundred collections, which have been obtained from temperate regions of North America during 1990 and 1991, are currently being screened in new bioassays; active sesquiterpene lactones have been recently isolated from species of Porella. The methodologies of collecting and screening bryophyte samples are discussed with consideration to costs based on expected number of samples that might be collected in a day, the diversity in the collections as related to phytogeography and vegetation types, and the bryophyte cover that is vanishing in many forest regions of the United States. The difficulties in obtaining large collections for isolation of active agents are also discussed by examplerecollection of Claopodium crispifolium.
Las comunidades de briofitas de troncos en descomposición del bosque subtropical mojado de Puerto Rico son descritas cuantitativamente. Los troncos en descomposición fueron clasificados de acuerdo a la presencia de corteza y textura de la madera. En los troncos con corteza dominan miembros de las Lejeuneáceas y Calymperáceas. En los de madera blanda son comunes Taxithelium planum e Isopterygium tenerum. De manera preliminar se sugiere que las briofitas higromórficas dominan en los troncos más descompuestos debido a la escasa fluctuación de la humedad en estos.
De las 21 especies neotropicales de Octoblepharum válidamente publicadas, se reconocen, al presente, sólo nueve. Estas son: O. albidum Hedw., O. ampullaceum Mitt., O. cocuiense Mitt., O. cylindricum Schimp. ex Mont., O. erectifolium Mitt., O. pulvinatum (Doz. & Molk.) Mitt., O. rhaphidostegium C. Müll., O. stramineum Mitt. y O. tatei (Williams) Bartr. Se distinguen dos líneas evolutivas de acuerdo al número de dientes del peristoma. Los miembros de la línea con 16 dientes son dioicos mientras que aquellos de la de 8 pueden ser autoicos o dioicos. Los estudios fenológicos en poblaciones de 3 especies en Panamá sugieren un pseudodioicismo en las especies autoicas con el desarrollo de gametoceos masculinos y anteridios en mayor número que los femeninos. En las poblaciones de O. albidum se presentan dos tipos de peristoma, uno verticalmente estriado y otro liso. Todas las especies ocurren en América del Sur la que se considera como el centro de origen y especiación del género.
Phenological observations and sex ratios in Marchantia chenopoda L. (Hepaticae: Marchantiaceae)
(1992)
Sex ratios were determined for 15 populations of Marchantia chenopoda L. along Puerto Rico. Sex was determined for twenty randomly selected individuals from each population. A female bias was observed in most populations. A census of reproductive structures of M. chenopoda was performed every two weeks in order to determine phenology. The highest archegoniophore count was observed to occur in January and February; minimum and maximum fertilization distances were 0.7 cm and 65 cm, respectively. Young sporophytes were most frequently observed at the beginning of the rainy season, in April and May. The highest frequency of mature sporophytes occurred during the dry season, in January and February. Capsules opened mostly during the heavy rainy season, from August to November. Protonemata were observed in the periphery of the population. Most young sporophytes aborted at the end of the moderate to heavy rainy season, from June to August. Immature gemmae cups were most frequent at the beginning of the rainy season, in April and May. Mature gemmae cups were observed throughout the rainy season, but were most frequent in September.
Cuba es uno de los países de las Antillas Mayores con mayor diversidad de musgos (383 taxa infragenéricos) los cuales se encuentran distribuidos fundamentalmente hacia las zonas montañosas. Aunque se han iniciado estudios en fitoquímica y antibiosis, los de sistemática deben continuar paralelamente.
Se presenta la ubicación taxonómica actualizada de 106 géneros de hepáticas y 233 géneros de musgos conocidos de Venezuela. Asimismo, se presenta una versión resumida de la distribución geográfica en Venezuela de 383 especies de hepáticas y 1009 especies de musgos. La información proviene principalmente de la revisión exhaustiva de las colecciones de briofitas en los herbarios venezolanos y de las publicaciones sobre briofitas colectadas en Venezuela. Se concluye que Venezuela, a pesar de haber sido poco explorada tiene una gran diversidad de briofitas, muchas de las cuales aún no se conocen y podrían extinguirse antes de haber sido colectadas, determinadas y analizadas científicamente.