Included here are the mountain systems of Mexico including the southern slopes of the Sierra Madre del Sur, the northern parts of the Sierra Madre Occidentale and Sierra Madre Orientale and the altiplane of central Mexico.

Mexican Highlands Oak-Pine Woodlands

Forests dominated by pine and oak can be found, for example, in the Sierra Madre de Oaxaca and the Sierra Madre del Sur where they start to develop at elevations of about 1600 m extending to about 2800 m. Tree species composition varies but may includes Quercus brachystachya, Q. castanea, Q. laurina, Q. magnolifolia, Q. obtusata and Q. rugosa, while common pine species are Pinus ayacahuite, P. chiapensis, P. cornuta, P. devoniana, P. hartwegii, P. montezumae, P. rudis and the endemic P. herrerai, P. lawsonii, P. leiophylla, P. oaxacana and P. rzedowskii (Pinaceae). Other trees include Arbutus xalapensis and the endemic or near endemic Engelhardtia mexicana and Oreomunnea mexicana (Juglandaceae). Engelhardtia is considered to be one of the most primitive members of the Juglandaceae. At shrub level ericaceous species are common and include Arctostaphylos conzattii, Vaccinium confertum and the endemic Pernettya mexicana (Ericaceae). Herbaceous ground layer species are also well represented with species such as Ascelpias circinalis, Ranunculus petiolaris, Viola hookeriana and the endemic Didymaea mexicana (Rubiaceae). At ground level these forests often have a temperate aspect, but that notion is dispelled by the abundance of epiphytic species such as the orchid Epidendrum vitellinum and the endemic fern Polypodium martensii (Polypodiaceae). The trees are typically festooned with vines such as Struthanthus deppeanus. Another outstanding feature of these forests is their huge level of endemism with at least five endemic genera, Hintonella (Orchidaceae), Microspermum (Asteraceae), Omiltemia (Rubiaceae), Pegritschia (Poaceae) and Silviella (Orobanchiaceae). Most of the endemic species are in the Monimiaceae or Rubiaceae (such as Rondeletia ginettei), while endemic species from other families include Anthurium cerroplonense (Araceae), Carica cnidoscoloides (Caricaceae), Siparuna scadens (Siparunaceae) and Synognium sagittatum (family?). These forests also provide habitat for two endemic relict species of the Commelinaceae: Gibasoides laxiflora and Matudanthus nanus, which are regarded as possible precursors of the genus Tradescantia.

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