Saturday 15 December 2018

Merostachys mexicana: A new species of Bamboo from Mexico.

Bamboos, Bambusoideae, are evergreen woody plants within the Grass Family, Poaceae. They are large for Grasses. with most species being shrubby, and some rainforest species forming tree-sized plants reaching over 30 m in height. This is particularly remarkable, as each Bamboo stem will reach this size in a single growing season (usually less than four months), with new shoots being produced from an underground rhizome (root-like stem) each growing season, and persisting for several years. In order to do this Bamboos have become the fastest growing plants on Earth, with speeds of up to a milimetre every 90 seconds recorded (which comes out at 4 cm per hour) over a meter in a day. Bamboos flower unfrequently, with many species able to go through many years of vegetative growth, before suddenly going through a flowering episode, co-ordinated over a wide area, to enable sexual reproduction; the most extreme example of this being a Chinese species, Phyllostachys bambusoides, which flowers only once every 130 years.

The genus Merostachys comprises 52 species of woody, rhizomatous Bamboos from Central and South America. The genus reaches its maximum diversity in the Atlantic rainforests of Brazil, where 41 of the known species are found, with nine described species from the rest of South America, and two from Central America, found in the montane cloud forests and rainforests of Belize, Costa Rica, Guatemala, Honduras, Nicaragua and Panama.

In a paper published in the journal Phytotaxa on 13 March 2018, Eduado Ruiz-Sanchez of the Departamento de Botánica y Zoología at the Universidad de Guadalajara, Lynn Clark of the Department of Ecology, Evolution, and Organismal Biology at Iowa State University, Teresa Mejía-Saulés of the Red de Biología Evolutiva at the Instituto de Ecología, and Francisco Lorea-Hernández of the Red de Biodiversidad y Sistemática at the Instituto de Ecología, describe a new species of Merostachys from southern Mexico.

The new species is named Merostachys mexicana, in reference to the country where it was discovered. It is a rhizomatous Bamboo, with visible stems growing at intervals from the underground rhizome. These erect stems reach 6-10 m in height, with a basal diameter of 1-2 cm. They grow erect originally, then adopting a climbing habit. Nodes are 30-45 cm apart, and produce leaves 25-35 cm in length or 10-25 flowering branches 20-56 cm long.

Merostachys mexicana. (A) Culm segment showing a culm leaf with its reflexed blade. (B) Internode showing two nodes and bud. (C) Detail of the apsidate (fan-shaped) early bud development. (D) Culm fragment showing the node and hollow culm with thin walls. (E) Culm fragment showing flowering branches. (F) Foliage leaf complement. (G) Inflorescence showing paired spikelets. (H) Spikelet lateral view showing the lower and upper glumes and lemma. Daniel Barba in Ruiz-Sanchez et al. (2018).

Merostachys mexicana was found growing at two locations, one in Tabasco State, and one in Chiapas, within the El Triunfo National Reserve, in montane cloud forests at altitudes of 1000 and 2080 m above sealevel, respectively. The montane cloud forests of Mexico are an important biodiversity hotspot, but are also a threatened environment, now covering less than half of their original extent. Due to the very small known population of the species, and its being found in a threatened environment, Ruiz-Sanchez et al. recommend that the species be treated as Critically Endangered under the terms of the International Union for the Conservation of Nature’s Red List of Threatened Species.

Merostachys mexicana. (A) New erect shoots, showing culm leaves. (B) Foliage leaves. (C) Abaxial side of the foliage leaf complement showing the marginal stripe (white arrow). (D) Foliage leaf complement showing the fimbriae (white arrow). (E) Old inflorescences. (F). Remnant new inflorescence showing spikelets and stamen. (G) Nucoid caryopsis (white arrow). Ruiz-Sanchez in Ruiz-Sanchez et al. (2018).

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