Mexican Highlands (Tehuacán Valley) Matorral
This distinctive cactus and thorn-shrub vegetation extends from Sierra de Zongolica in the Sierra Madre Orientale in the north to Sierra de Juárez in the south and has been regarded as a floristic province in its own right. The flora has four endemic angiosperm genera (Gypsacanthus, Oaxacania, Pringleochloa and Solisia) and a multitude of endemic species - in the Asteraceae alone there are 50 endemic species. In addition 55% of all Mexican columnar cacti, 30% of which are endemic, occur here, and the area is considered to be a centre for the origin and diversification of the genus Agave. The vegetation has a maximum height of about 8 m but it is often much less than this. In fact, the structure can be quite varied, but it is only when plants are in full bloom that the tremendous variety can be appreciated. The trees are usually umbrella shaped with contorted branches and often have smooth boles or peeling bark typical of arid zones. Common trees include Acacia subangulata, Cassia pringlei and the endemic Mimosa luisana (Fabaceae). The endemic Morkillia mexicana (Zygophyllaceae) can also be particularly evident when bearing it large magenta flowers. Another distinctive species is the endemic Thouinidium insigne (Sapindaceae) with its inflated, winged clusters of fan fruit. But among the most unusual trees are the endemic Jatropha neopauciflora (Euphorbiaceae) with its thick branches, and the endemic Manihot pauciflora (Euphorbiaceae) with its Oxalis-like foliage. Rising above the trees are various columnar and candelabra cacti. One other most conspicuous of the latter is the endemic Escontria choitilla (Cactaceae) with its distinctive yellow flowers. The shrub layer includes compact forms, such as the endemic Bursera arida (Burseraceae) and others that are tortuously intertwined. Many have inconspicuous flowers, but others such as the endemic Ayenia fruticosa (Malvaceae) and Perymenium ovata (Asteraceae) are much more showy. Also at shrub heights are numerous rosettes of Agave plants such as the endemic Agave rubescens (Agavaceae). The herbaceous flora is also surprisingly varied with species such as the endemic Argemone mexicana and Sanvitalia fruticosa (Asteraceae), but another fascinating feature of this vegetation is the presence of the giant horsetail Equisetum giganteum, which can reach heights of 4 m. It is confined to moist areas and can often be found adjacent to streams. Among the many other endemic species of this unique community are Beaucarnea gracilis (Agavaceae), Echeveria subsessilis (Crassulaceae), Ferrocactus robustus (Cactaceae), Fouquieria purpusii (Fouquieriaceae), Grabowskia geniculata (Solonaceae), Jacquemontia smithii (Convolvulaceae), Lasiocarpus ovalifolius (Malpghiaceae), Neobuxbaumia tetetzo (Cactaceae), Pachycereus hollianus (Cactaceae) Pedilanthus cymbifera (Euphorbiaceae), Pterostemon mexicanus (Pterostemonaceae) and Yucca periculosa (Agavaceae).
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.
Further information required.
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