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polylepis
''Polylepis'' (pronounced pah-lee-LEE-piss or pah-lee-LEH-piss) is a genus comprising twenty eight recognised shrub and tree species, that are endemic to the mid- and high-elevation regions of the tropical Andes.〔Simpson, Beryl B. "A Revision of the Genus Polylepis (Rosaceae: Sanguisorbeae)." Washington, D.C.: Smithsonian Institution Press, 1979. Vol. Smithsonian Contributions to Botany. Print〕 This group is unique in the rose family in that it is predominantly wind-pollinated. They are usually gnarled in shape, but in certain areas some trees are 15–20 m tall and have 2 m-thick trunks. The foliage is evergreen, with dense small leaves, and often having large amounts of dead twigs hanging down from the underside of the canopy. The name ''Polylepis'' is, in fact, derived from the Greek words poly (many) plus letis (layers), referring to the shredding, multi-layered bark that is common to all species of the genus.〔 The bark is thick and rough and densely layered for protection against low temperatures.
Some species of ''Polylepis'' form woodlands growing well above normal tree line within grass and scrub associations at elevations over 5000 m; which makes ''Polylepis'' appear to be the highest naturally occurring arborescent angiosperm genus in the world.〔
==Classification/Taxonomy==
The genus ''Polylepis'' is very complicated taxonomically. It contains about twenty species that are distributed across the Andes. It is in the rose family, Rosaceae. The genus belongs to the tribe Sanguisorbeae, which mainly comprises herbs and small shrubs.〔Robertson, K. R., 1974: The genera of the Rosaceae in the southeastern United States. – J. Arnold Arboretum 55: 303-332, 344-401, 611-662〕 Although the relationship of ''Polylepis'' to other genera of Sanguisorbeae is largely unknown, the analysis of Erickssonn et al. (2003) showed evidence of a close relationship between ''Polylepis'' and Acaena,〔Kerr, Malin. "A phylogenetic and Bilgeographic Analysis of Sanguisorbeae (Rosaceae). With Emphasis on the Pleistocene Radiation of the High Andean Genus Polylepis". University of Maryland, 2004 ()〕 which shows tendencies towards having fused stipular sheaths, reddish, flaking-off bark, and axillary, somewhat pendant inflorescences, features otherwise characteristic of ''Polylepis''.〔Fjeldsa, Jon, and Michael Kessler. "Conserving the Biological Diversity of Polylepis Woodlands of the Highland of Peru and Bolivia." A Contribution to Sustainable Natural Resource Management in the Andes. Eds. Engblom, Gunnar and Peter Driesch. Copenhagen, Denmark: NORDECO, 1996. Print.〕 There are several characteristics that are important taxonomically to distinguish between species of ''Polylepis'', for example: 1) The amount of leaf congestion, 2) presence or absence of spurs and their size and vestiture, 3) presence or absence and type of trichomes, (4) size, shape, thickness and vestiture of leaflets. The most important taxonomic character, however, is the leaflets.〔
Studies suggest that repeated fragmentation and reconnection of páramo vegetation, caused by the Pleistocene climatic fluctuations, had a strong influence on the evolution and speed of speciation in the genus ''Polylepis'' as well as the páramo biota as a whole.
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