This "Páramo ecosystem" website is based primarily upon information published in the book Páramos: A Checklist of Plant Diversity, Geographical Distribution, and Botanical Literature (Luteyn, 1999, Memoirs of the New York Botanical Garden Volume 84).

Espeletia

U-shaped valley

Lake Patoquinoas

"The páramo zone is the most interesting of the life zones of the Andes, since it shows to the highest degree, the struggle of plant and animal life against conditions of extreme cold temperature..." 

(Chardón, 1933)

General Definition

      Within the tropical regions of Mexico, Central and South America, Africa, Malesia including New Guinea, and Hawaii, there is a vegetation type that occurs between the upper limit of continuous, closed-canopy forest (i.e., forest line or timberline) and the upper limit of plant life (i.e., snow line) that is characterized by tussock grasses, large rosette plants, shrubs with evergreen, coriaceous and sclerophyllous leaves, and cushion plants.  This vegetation type is scattered along the crests of the highest mountain ranges or on isolated mountaintops between about 3000 meters (m) and 5000 m, like islands in a sea of forest.  Locally these areas are known as "zacatonales" (the Mexican and Guatemalan volcanic highlands), "páramo" (Central and northern South America), "jalca" (northern Peru), "puna" (drier areas of the altiplano of the central Andes), "afroalpine" and "moorland" (East Africa), and "tropical-alpine" (Malesia).
      Although neither Beard (1944), Troll (1958), nor Lauer (1981) felt the term "alpine" was appropriate for inter-tropical high altitude landscapes, these vegetation types have been more recently referred to as "tropical alpine" (Ramsay & Oxley, 1997;  Rundel et al., 1994;  Smith & Young, 1987) or "tropicalpine" (Smith & Cleef, 1988).  I do not like to apply the general term "alpine" to vegetation in the tropics, because it is a term derived from temperate regions.  Furthermore, high elevation tropical climates differ sharply from those of temperate alpine regions, particularly with respect to seasonality and diurnal patterns of temperature change (Rundel, 1994).  Some authors, including Walter (1973), Lauer (1981), and Monasterio and Vuilleumier (1986), advocate using the term páramo in the broadest sense possible, on a worldwide basis, for all high tropical montane vegetation above the continuous timberline for the sake of nomenclatural simplicity, if for no other reason.  Monasterio and Vuilleumier would simply add a geographic adjective to characterize the particular area being discussed, for example, Andean páramo, African páramo, etc.  Andean páramo is often compared with other alpine and arctic ecosystems (Baruch, 1979;  Billings, 1973, 1974, 1979;  Billings & Mooney, 1968;  Smith & Young, 1987).  For the purposes of this book, the term "páramo" is used in its regional sense, being restricted to the northern Andes of South America and adjacent southern Central America.  It is here used as a collective term for the entire landscape unit (or ecosystem) of the high altitude above continuous forest line and below the perpetual snow line.  Many different plant communities can be found in páramo, and will be discussed below, but the most widespread are dominated by tussock-forming grasses.
      The word páramo comes from the Latin word "paramus", according to the Diccionario de la Lengua Española (Real Academia Española, 1992).  Corominas (1973) states that this Hispanic-Latin word seemingly arose from the mid-western portion of the northern Iberian Peninsula, but that its exact origin is uncertain.  He further suggests that it may have been adopted by the Romans as a celticism, or instead is neither Iberian nor Celtic but originates from another Indoeuropean language in pre-Roman times.  In Spain, up until the epoch of the Conquest, the desertic plateau of arid Castile, which contrasts with the fertile regions lower down, was called "paramera."  Font Quer (1977) states that in Castilian Spanish the general significance of the word páramo is a flat plain.  The early Spanish explorers applied the word páramo to north Andean areas that were high, cold, inhospitable, wind- and rainswept, perhaps reminding them of the plains in their native Iberian Peninsula.  In Colombia, atmospheric moisture in the form of drizzle is often referred to as "paramitos," while in Ecuador the term "parameando" has come to mean "it is raining," and in Venezuela one might say "estoy emparamado" when one is getting wet because of rain and cold (Monasterio, 1980b;  Nuñes & Pérez, 1994;  Ramsay, 1992;  Vareschi, 1970;  Weber, 1958;  pers. comm. with local inhabitants).  For definitions and insight into conceptualizations of the páramo ecosystem by local "parameros" (inhabitants of the páramos), see López-Zent (1995) and Zambrano (1993).
      The páramo landscape has been influenced by glaciation. It is irregular and uneven, from jagged and very rough with erratic rocks to rolling or flat, often times with many small glacial lakes and tributaries.  It is the source of many of the large rivers of northern South America (e.g., Río Magdalena and Río Cauca of Colombia, Río Napo and Río Coca of Ecuador, and Río Orinoco of Colombia and Venezuela).  As will be seen from the discussions in this Introduction, there is no single definition of páramo, because it is characterized by a variety of geographic, geologic, climatic, physiognomic, and floristic features, all of which will be briefly touched upon.

Geographical Distribution

      In the tropics of the Americas, the páramo ecosystem is discontinuously distributed between 11°N and 8°S latitudes.  It is concentrated in the northwest corner of South America, mostly in Venezuela, Colombia, and Ecuador, but there are outliers in Costa Rica, Panama, and northern Peru (see front and back endpapers, which show in black the area above 3000 m elevation that is potentially páramo).  The northernmost páramos are located in the Sierra Nevada de Santa Marta of Colombia, located at about 11°N latitude.  The westernmost páramos are located in Costa Rica, in the Cerro Buena Vista (Cerro de La Muerte) region of the Cordillera de Talamanca, at about 83°W longitude.  The easternmost páramos are located in north-central Venezuela, in the state of Lara, at about 70°W longitude.  The southernmost páramos (locally called "jalca") are found in northern Peru in the department of La Libertad, at about 8°S latitude, just north of the Cordillera Blanca.  Other neotropical areas that have páramo-like vegetation or that correspond ecologically and have sometimes been referred to as páramo, but that fall outside the geographical range or definition used in this book, include Pico Duarte in the Dominican Republic, the "zacatonales" of Mexico, Pico Naiguatá (Avila and the Silla de Caracas areas) in the Cordillera Costal of north-central Venezuela, Pico de la Neblina along the Venezuela/Brazil border, scattered "humid puna" areas of the eastern slopes of the Peruvian Andes, the "yungas" region of northeastern Bolivia, scattered areas in Chile and Argentina, and the Itatiaia area of eastern Brazil.
      For other opinions about the geographical distribution of páramo, see Brack Egg (1986b), Braun (1956), Cleef (1978, 1981b), Cuatrecasas (1968), Mann (1968), Monasterio (1980b), ONERN (1976), Ribera et al. (1994), Tosi (1960), Unzueta Q. (1975), Vareschi (1955), and Vuilleumier and Monasterio (1986).

Climate

Cloud-free, cold, crisp

Fog, and drizzle

Snow

      The páramos of Colombia and northern Ecuador are influenced by the intertropical convergence of air masses (a low pressure trough), because of their geographical location near the Equator.  They are generally humid throughout all or most months of the year with continuous moisture in the form of rain, clouds, and fog, mostly due to orographic uplift caused by the Andes.  Many páramos receive more than 2000 mm of rain on their exposed slopes (absolute range 500-ca. 3000 mm/year).  They have a high relative humidity averaging 70-85% (absolute range 25-100%).  This contrasts with páramos in the northernmost Andes of Venezuela, the Sierra Nevada de Santa Marta in northern Colombia, and in Costa Rica, where there is a marked dry season due to the influence of the northeast Trade winds (Herrmann, 1970, 1971;  Lauer, 1979a,b).  Páramo becomes driest near its southern limits in southern Ecuador and northern Peru, where they are influenced by two air masses, one from the Amazon Basin, which has already released its moisture on the eastern slopes, and another dry cool air mass from the West under the influence of the Humboldt Current.  In addition to the large scale climatic parameters given above, local microclimates may strongly influence regional weather patterns (G. Sarmeinto, 1986).  In northern Peru, the páramo environment grades almost imperceptibly into the "puna" ecosystem, which is more characteristic of the central and southern Andean altiplano highlands of central Peru, Bolivia, and Argentina.  Puna, in contrast to páramo, is typically xeric with lower humidity, a shorter wet season, and six months or more of almost no rain.  Figure 5 illustrates the overall climate of páramo by the use of climate diagrams from scattered localities.  For additional climate diagrams, see Cañadas Cruz (1983), Cleef (1981b), Guhl (1982), Jørgensen and Ulloa U. (1994), Monasterio and Reyes (1980), Van der Hammen et al. (1995), and Witte (1994).  For comparisons of páramo and puna, see reviews by Cabrera (1957, 1968, 1976), Lauer (1952), Quintanilla P. (1983), G. Sarmiento (1986), Troll (1968b), and Young et al. (1997). 
      Páramos have a generally cold and humid climate with sudden changes in the weather and a diurnal fluctuation in temperature from below freezing to as much as 30°C, which often results in a daily freeze-and-thaw cycle that has been referred to as "summer every day and winter every night" (O. Hedberg, 1964).  During the dry season, for example, Páramo Piedras Blancas (Venezuela), at 3700-4700 m elevation, shows extremes in air temperatures ranging from -5°C to -11°C at night to 25-30°C during the day, with freezing temperatures occurring 325-350 nights of the year (Pérez, 1987a, 1996b;  Pfitsch, 1994).  Although overall mean annual temperatures of páramo range from 2°C to 10°C, there is much greater contrast in the climate of higher elevation areas than is found in lower zones of the same mountain ranges.  Therefore, the environment becomes harsher and more severe for plant life as altitude increases (Javellas & Thouret, 1995).
      A typical day often begins cloud-free, cold, crisp, and occasionally windy until mid morning; then increased cloud cover from lower elevations, caused by convectional and orographic uplift, brings rain, sleet, fog, and drizzle for much of the afternoon;  clearing often occurs in the late afternoon or early evening.  Nights are always cold and usually clear with stars filling the skies;  however, frost is frequent in the high páramos and snow is common at the highest altitudes. During any given day of the year rain, ice, snow, and fog may alternate abruptly with clear sunny skies and elevated temperatures;  in one moment the wet cold necessitates heavy clothing, raincoats, and gloves, while in the next moment, lotion is needed to protect against sunburn.
      For other general references that discuss páramo climate, see Cuatrecasas (1968), Eidt (1968), Guhl (1974), Lauer (1981), Monasterio (1980a), Rundel (1994), Schnetter et al. (1976), J. Snow (1976), Sturm (1978), Sturm and Rangel Ch. (1985), Troll (1968b), Van der Hammen and Ruiz (1984), Van der Hammen and Santos (1995), Van der Hammen et al. (1983, 1989, 1995, In press), Weber (1958), and Witte (1994).

Soils

      The geology of the Andes is extremely variable and consequently so are the soils.  Most páramo soils are relatively young and only slightly developed, and are broadly classified into the orders Andosols, Inceptisols, Histosols, Entisols, and Mollisols (Buol, et al., 1980;  Buringh, 1979;  FAO, 1975;  Soil Survey Staff, 1975).
      Andosols and Inceptisols include older soil names such as Ando soils, brown tropical soils, black soils, Onji soils, humic allophane soils, hydro humic latosols, volcanic soils, and volcanic ash soils.  They are soils formed from and associated with volcanic ash, have a low supply of (or have lost) bases or iron and aluminum, and show moderate weathering.  In páramo, these may include Andepts and some Aquepts, as well as Tropepts and Umbrepts.  The Andosols most likely to form in páramos are Aquands, Cryands, and Udands.
      Histosols include older soil names such as bog soils, muck soils, organic soils, and peat soils.  They are soils that are highly organic and are found in very wet places such as bogs and swamps.  These may include Fibrists, Folists, Hemists, and Saprists.
      Entisols are soils that have little or no evidence of development (i.e., absence of horizons) and have a highly mineral nature.  These are often found near snow line and may include Aquents, Fluvents, Orthents, and Psamments.
      Mollisols are a less common soil group in the páramo, but are very dark colored and base-rich.  The most likely group to develop are the Aquolls.
      At its highest elevations (i.e., superpáramo), páramo soils are very shallow and coarse with a high percentage of rock and sand, there is little to no production of organic matter, and consequently, low water retention. Superpáramo soils are extremely infertile since without organic matter or fine grains they have practically no ability to hold exchangeable cations (Pérez, 1992c).  Furthermore, in the superpáramo, the soil surface is recurrently disturbed by needle-ice activity (a type of ground frost), and soil-moving phenomena such as frost-heaving and thawing and sorting of material is common (Pérez, 1987c).  In this part of the high páramo, the mean annual air temperatures are always low (4-6°C), but the cold does not penetrate very deeply into the soil.  Soil temperatures, at about 30 cm, more or less reflect those of the mean annual temperatures of the air (Lauer, 1979).  Soil temperature does, however, have a profound effect on nutrient and water availability, root growth, seed survival and germination, and vegetation zonation (Diemer, 1996;  Lauer, 1981;  Pérez, 1987b;  A. P. Smith, 1976;  Walter & Medina, 1969).
      At its middle elevations (i.e., grass páramo), páramo soils are relatively deep, humic, black or dark brownish, and acidic with pH ranging from about 3.7 to 5.5.  They are continuously moist or even saturated with water due to the daily formation of dew or frost and the water-retaining capabilities of the highly organic, peat-like content.
 In the lowermost part of the páramo (i.e., subpáramo), near Bogotá (Colombia) and elsewhere in the northern Andes, Sturm (1978) has stated that soils have in common:  dark color ("black coloured"), moderate to high pH and correspondingly low Ca levels, low free P content, relatively high K and N content and reduced uptake of these elements by plants, higher than 10% organic content in the top layer, little or no "podzolic" features, and high water capacity.
      For a discussion of the factors that help to form páramo soils, see Cortés Lombana (1982, 1995).  For soil types in local páramo studies, see Baruch (1979), Botero (1985), Hofstede (1995c), Pérez (1991c, 1992c, 1996b), Quintanilla P. (1983b), Rangel Ch. (1989), Salomons (1986), Sánchez M. et al. (1989), Sevink (1984), Sturm and Rangel Ch. (1985), Thouret and Faivre (1989), and Vis (1995).  For other general references about páramo soils, see also Del Llano (1990), Jenny (1948), Jenny et al. (1948), Simonson (1979), Sturm (1994a), Van der Hammen and Ruiz (1984), Van der Hammen and Santos (1995), Van der Hammen et al. (1983, 1989, In press), Vareschi (1970), Wright and Bennema (1965), and Zöttle (1970).

Paleohistory and Paleoecology

      Reconstruction of the paleoecology of páramo and high elevation montane forest has been the subject of study by Thomas Van der Hammen and his associates since the 1960s.  The following is a brief summary of an article by Van der Hammen and Cleef (1986) that emphasizes the paleohistoric events that gave rise to and further influenced development of the páramo ecosystem we see today in the high plain of Bogotá (Colombia).  The sequences may be similar or different in other parts of the northern Andes.  Unfortunately, detailed accounts from other areas are few or not yet available.
      The Andes began to arise during the Paleocene, and during the Miocene they were probably only ridges to low mountains up to ca. 1000 m elevation.  It was not until the beginning of the Pliocene or slightly later that the northern Andean region uplifted to its present altitudes.  During the Plio-Pleistocene, ca. 4-5 Ma (million years ago) there was abundant volcanic activity, at which time elevations above the present treeline came into being.  There may not have been forest yet at the high elevations, since considerable time was needed for the forest line to have risen from around 2500 m (the level at that time) up to around 3500 m.  The upper Andean forest and páramo belts evolved more or less simultaneously during the Late Pliocene or Early Pleistocene (2-4 Ma).  There is evidence that an early páramo vegetation, what Van der Hammen and Cleef call "protopáramo" vegetation, was present and consisted of Poaceae, Cyperaceae, Asteraceae, Ericaceae, a Polylepis-Acaena (Rosaceae) type of pollen, and Symplocos (Symplocaceae), Myrica (Myricaceae), Aragoa (Scrophulariaceae), Hypericum (Clusiaceae), Miconia (Melastomataceae), Ilex (Aquifoliaceae), Hydrocotyle (Apiaceae), Borreria (Rubiaceae), Ludwigia (Onagraceae), Polygonum (Polygonaceae), Valeriana (Valerianaceae), Plantago (Plantaginaceae), Ranunculus (Ranunculaceae), Myriophyllum (Haloragaceae), Jamesonia (Pteridaceae), and Hymenophyllum (Hymenophyllaceae).  By 1 Ma (for the high plain of Bogotá, Colombia, at about 2600 m), there is evidence for about 15 to 20 repeated alternations of forest and páramo (i.e., fluctuations of climatic zones) in interglacial and glacial periods. During this time genera of north temperate origin, such as Alnus (Betulaceae) ca. 1 Ma and Quercus (Fagaceae) ca. 0.3 Ma, appeared in the pollen record and must have passed over a Panamanian landbridge.
      During the later part of the Quaternary, ca. 44,000-21,000 yr BP (before present) of the Last Glacial stadial, glacials and interglacials continued to alternate with some short but severe cold periods.  At that time there were numerous changes in the proportions between páramo and forest elements, although the páramo flora became well established and dominated the scene.  Between ca. 45,000 yr BP and 25,000 yr BP there was a cold and wet period during which time glaciation reached its maximum advance.  Van der Hammen and Cleef further explain that during this time the glaciers and forest may even have been in contact at elevations between 2200 m and 2700 m, and the páramo belt must have been relatively narrow and wet.  On the contrary, between 21,000 yr BP and 14,000 yr BP there was a very cold but dry period during which time the mean annual temperature may have been 6-7°C lower than today.  Glaciation was not so extensive, but the páramo belt was broad and dry and covered most of the area above 2000 m (i.e., the area where present-day forest occurs).  This means that páramo vegetation covered a much greater area than it does today, and that many of the currently isolated páramos were then united.  It also means that the upper forest line was lowered by 1300-1500 m.
      At the beginning of the Holocene (ca. 10,000 yr BP) the climate became much warmer;  forest limits rose to elevations even higher than today and páramo vegetation was restricted to above 3300-3500 m.  The lower elevation forest included Dodonaea viscosa (Sapindaceae), Myrica (Myricaceae), Myrsine (=Rapanea) (Myrsinaceae), and Miconia (Melastomataceae);  it continued upwards with Alnus (Betulaceae), and ended at the highest elevations with Weinmannia (Cunoniaceae) and Quercus (Fagaceae).  During the period from 7500 yr BP to ca. 3000 yr BP temperatures rose about 2°C more, causing another upward shift in the forest line of about 300-400 m higher than today, and thereby reducing the area occupied by páramo.  Finally, at about 2900 yr BP, there was a noticeable lowering of the temperature that marked the last downward movement of the forest and páramo belts to their present-day positions.  Van der Hammen and Cleef state that the most important changes in the Holocene period have been the temperature changes mentioned above, the development of soils, and the development of peat bogs and soils with increased humidity.  They summarize by saying that the present-day páramo flora and vegetation is the result of an amalgamation of approximately 4-5 million years of complicated paleohistoric events.
      Some recent publications suggest that the situation may be more complex or may differ in other parts of the Andes than that described by Van der Hammen and Cleef (1986).  Colinvaux et al. (1997), for example, refute Van der Hammen's idea that Andean vegetation zones were compressed and moved in belts during Quaternary times.  Instead they suggest that during times of glacial cooling or Holocene warming plant associations showed different spatial diversity and were reformed according to the temperature tolerance of individual species, with heat intolerant species showing larger displacements.
      For additional general references about geology, glaciation, and paleohistory in the páramo regions of Central and South America, see Horn (1990b) and Weber (1958) for Costa Rica;  Graham (1973, 1989) and Markgraf (1989) for general Central and South America;  Salgado-Labouriau (1986) and Schubert and Vivas (1993) for Venezuela;  Helmens (1990), Hooghiemstra and Ran (1994), Van der Hammen (1981b, 1989), and Van der Hammen et al. (1973) for Colombia;  and Colinvaux et al. (1997), Hastenrath (1981), and Wolf (1892) for Ecuador.

Vegetation Zonation

Arenal del Cerro Amarillo

Laguna Patoquinoas

Páramo arbustivo

      Over the years numerous authors have given various names to the different vegetation zones and plant associations within the high Andes.  At times the usage of these names can become confusing and it is difficult to know exactly what is being discussed and/or compared, but see Huber and Riina (1997) and Jørgensen and Ulloa U. (1994) for summaries of this nomenclature.  When thinking of or talking about páramo, for example, reference is generally being made to the open, treeless grasslands with scattered espeletias and shrubs.  Much of the present day páramo vegetation of treeless grasslands, however, probably has anthropogenic origins, being maintained by cutting, periodic burning, and grazing;  practices mostly intensified within the last 300 years.  Therefore, the natural forest line at which forest ends and undisturbed páramo begins was probably higher than what is seen today and above 4000 m elevation in some places.  The evidence for this is that in an undisturbed system, there is usually not an abrupt end to the forest, not a sharp edge or border, but instead more of a transition from the tall forest trees to gradually shorter trees with increased elevation, then small trees and shrubs in a more or less thicket formation, and finally, above the forest line to the grasses, herbs, and scattered small shrubs of páramo. As one reaches the natural limits of one zone with the next, many of the plant species characteristic of these zones intermix.  It must also be remembered that the boundaries of the vegetation zones and the elevations at which they begin and end are not fixed.  Depending on environmental features, such as topography, exposure, soils, and general climatic conditions, and human intervention, timberline may occur anywhere between about 2800 m and 4000(-4800) m in the northern Andes.  Furthermore, on the wetter or windward side of a mountain or cordillera, the boundary between forest and páramo (i.e., the contiguous forest line) is higher than on the dry or leeward side (Lægaard, 1992;  Lauer, 1981, 1993;  A. P. Smith, 1975b,c, 1994;  Troll, 1958, 1959, 1968b, 1973;  Verweij, 1995).
      This book follows Cuatrecasas (1934, 1954, 1958, 1968) in dividing páramo ideally into three broad zones based on overall altitude and vegetation structure, with varying degrees of intergradation.  From the highest elevations to the lowest, these three zones are called superpáramo, páramo (here referred to as grass páramo), and subpáramo.  Superpáramo may be looked upon as the transition belt or ecotone between the permanent snow region above and the grass páramo below.  Subpáramo may be seen as the transition belt or ecotone between the grass páramo above and the montane forest below.  A brief summary of these three zones follows.  Other ideas of páramo zonation or modifications of Cuatrecasas' ideas may be found in papers by Monasterio (1980c) and Vareschi (1970) for Venezuela, by Cleef (1981b), Espinal and Montenegro (1963), Fosberg (1944), and Guhl (1982) for Colombia, by Acosta-Solís (1984), Cañadas Cruz (1983), Harling (1979), Jørgensen and Ulloa U. (1994), and Ramsay (1992) for Ecuador, by Brack Egg (1986b) for Peru, or by Cabrera (1957), Fosberg (1967), and Holdridge (1967) for more general systems of overall vegetation classification that include páramo.

      Superpáramo.  This is a narrow zone of vegetation growing on rocky scree and coarse, sandy soils below the snow-line from about (4000-)4500-4800(-5000) m altitude. Amongst the three páramo zones it is characterized by the lowest air temperature, precipitation, soil water-holding capacity, and nutrient content, and the highest solar radiation and night-frost frequency (Baruch, 1984).  Plants in this zone must be capable of enduring the daily extreme conditions of coldness and strong radiation, and regular or frequent snowfalls.  Superpáramo is the zone of least disturbance by man.  It is very localized because of its scattered occurrence only on the highest mountains and has very high endemism.  Some superpáramos occur on mountaintops that are high enough in elevation to have glaciers in their uppermost regions, while others are without permanent snow.  Vegetation referred to as desert páramo, or sometimes locally called "arenales," may have so much sand that they look like beaches.
      At first glance, superpáramo often looks from a distance to be bare ground, but is in reality home to tiny, clumped or scattered plants, such as Azorella pedunculata (Apiaceae), Hypochaeris sessiliflora, Senecio canescens, S. nivalis, S. adglacialis, S. supremus, S. comosus, Pentacalia gelida and Xenophyllum rigidum (=Werneria rigida) (Asteraceae), Draba pachythyrsa, D. depressa and Eudema nubigena (Brassicaceae), Arenaria spp. and Cerastium floccosum (Caryophyllaceae), Pernettya prostrata and Disterigma empetrifolium (Ericaceae), Astragalus geminiflorus, Lupinus alopecuroides, L. microphyllus and L. smithianus (Fabaceae), Geranium multipartitum (Geraniaceae), Luzula racemosa (Juncaceae), Nototriche jamesonii and N. chimborazoensis (Malvaceae), Aciachne pulvinata, Agrostis nigritella, Bromus oliganthus, Poa cucullata, P. trachyphylla, P. orthophylla and Stipa ichu (Poaceae), Plantago sericea ssp. nubigena (Plantaginaceae), Valeriana alpifolia (Valerianaceae), Viola pygmaea (Violaceae), the only páramo gymnosperms Ephedra americana and E. rupestris (Ephedraceae), and various species of cryptogams including vagrant ball-forming mosses and unattached lichens.

Viola pygmaea

Ourisia chamaedrifolia

Ephedra americana

      Grass Páramo.  [Cuatrecasas referred to this zone as grass páramo, "páramo propiamente dicho", or páramo proper.]  From about 3500-4100(-4400) m vegetation of the grass páramo is continuous and plant cover is generally 100%. It is composed mainly of tussock- or bunch-grasslands dominated by species of Calamagrostis and/or Festuca.  There is a high proportion of dead shoots among the living that give a yellowish- or olive-brown to grayish look to the grasslands as a whole (Penland, 1941).   This is the classic area of the genus Espeletia and its relatives (Asteraceae: Espeletiinae), in local communities called "frailejonales", which for so many have come to symbolize páramo vegetation with their columnar, woolly, rosette-plant growth form. During October and November, in the higher Venezuelan páramos, there is no greater display of brilliant floral colors anywhere than when Espeletia schultzii (deep yellow) and Senecio formosus (violet-maroon) (Asteraceae), Castilleja fissifolia (bright red, yellow, and green) (Scrophulariaceae), and Chaetolepis lindeniana (intense magenta) (Melastomataceae) are in full bloom.
      The grass páramo is the most broadly circumscribed of the three páramo zones.  It includes not only the dominant grassland communities, but also the greatest number of azonal communities, which are determined by specific factors such as soil moisture and topography, and páramo growth forms.  The most frequently encountered azonal communities are described below under the grass páramo, but several are also found to a limited extent in the superpáramo and subpáramo zones as well.  The grassland communities of the grass páramo zone have suffered greatly from burning and grazing (see Impact of Burning and Grazing below).
      Grass páramo may consist of tall- and short- grass communities ("pajonales", "pastizales", or "prados") that include both herbaceous and woody vegetation, but they are dominated by tussock- or bunchgrasses. In the tall grass communities, with grass up to 1 m tall, Calamagrostis recta usually dominates on drier sites, while C. effusa dominates on moister.  Short grass communities usually indicate grazing and burning pressures and are often dominated by species of Agrostis, Festuca, and Paspalum.  The grass Aciachne pulvinata often forms low or flat cushions with very sharp (to the touch) leaves in drier-site short-grass páramos.  In Colombia, dwarf bamboos (Chusquea spp.) dominate on slopes with very wet climates in communities known as bamboo-brakes or "chuscales".
      If one takes the time to search between the bunchgrasses of the open grass páramo, there is an astonishing array of species of small herbs, e.g., Bomarea spp. (Alstroemeriaceae), Eryngium humile (Apiaceae), Perezia spp. (Asteraceae), Lysipomia spp. (Campanulaceae-Lobelioideae), Paepalanthus (Eriocaulaceae), Lupinus spp. (Fabaceae), Gentiana sedifolia, Gentianella spp. and Halenia spp. (Gentianaceae), Lachemilla spp. (Rosaceae), Gunnera magellanica (Haloragaceae), Sisyrinchium spp. and Orthrosanthus chimboracensis (Iridaceae), Oenothera epilobiifolia (Onagraceae), Ranunculus spp. (Ranunculaceae), Castilleja fissifolia and Bartsia spp. (Scrophulariaceae), the lycopods Huperzia spp., and the fern genus Jamesonia (Pteridacae). Common species rooted within the tussock formations include Cerastium spp. (Caryophyllaceae), Vicia andicola (Fabaceae), Geranium spp. (Geraniaceae), and Bromus lanatus (Poaceae).  Rumex acetosella (Polygonaceae) is a weedy adventive species that often forms a red landscape over large disturbed areas, usually after potato or wheat cultivation. Senecio niveo-aureus (Asteraceae) and related species in Senecio sect. Culcitium  add a stark beauty with their dense, woolly, whitish to pale yellowish pubescence, which covers practically the entire plant.  Acaulescent rosette-plants in the genera Oreomyrrhis (Apiaceae), Hypochaeris (Asteraceae), Acaulimalva (Malvaceae), and Acaena (Rosaceae), and cushion-plants in genera such as Werneria and Xenophyllum (Asteraceae), Draba (Brassicaceae), Arenaria (Caryophyllaceae), and Paepalanthus (Eriocaulaceae) are also common in the grass páramo.  Grass páramo is also rich in small and large shrubs, such as those genera mentioned in the subpáramo (below), but they are more scattered in the grass páramo. They include many species of Baccharis, Diplostephium, Gynoxys, Loricaria and Pentacalia (Asteraceae), Hypericum(Clusiaceae), Gaylussacia, Gaultheria, Pernettya and Vaccinium (Ericaceae), Arcytophyllum (Rubiaceae), and Valeriana (Valerianaceae).
      Swampy or boggy azonal sites, called cushion mires or "turberas", are common, especially in the uppermost grass páramo (Bosman et al., 1993;  Cleef, 1980a. Here species of the spectacular cushion plant growth form attain their best development, e.g., Azorella aretioides, A. multifida and A. pedunculata (Apiaceae), Oreobolus obtusangulus (Cyperaceae), the moss-like Distichia muscoides (Juncaceae), and Plantago rigida (Plantaginaceae).  The long-lived cushions often form the substrate for other smaller plants such as Hypochaeris spp. (Asteraceae), Carex spp. (Cyperaceae), Disterigma empetrifolium and Pernettya prostrata (Ericaceae), Gentiana sedifolia and Gentianella spp. (Gentianaceae), Agrostis spp. and Poa spp. (Poaceae), and Lachemilla spp. (Rosaceae).  These cushion "epiphytes" derive their water and nutrients from the process of litter decomposition and nurient release taking place within the cushion itself (Sklenár, 1998).  Other common species of swampy or boggy sites include Juncus spp. (Juncaceae), the páramo endemic Castratella piloselliodes (Melastomataceae), and Valeriana spp. (Valerianacee).  The lichen genera Cladia (Cladoniaceae) and Usnea (Parmeliaceae), mosses Campylopus (Dicranaceae), Breutelia (Bartramiaceae), Sphagnum (Sphagnaceae), and liverworts Riccardia (Aneuraceae), Frullania (Jubulaceae), and Lophozia (Jungermanniaceae) are also sometimes abundant.
      Other wet or flooded azonal communities such as marshes ("pantanos" or "ciénagas"), seeps, and springs, may also include bunchgrasses (especially Festuca dolichophylla), but with more species of sedges (Carex, Eleocharis, etc.) and mosses such as Drepanocladus (Amblystegiaceae) and Sphagnum (Sphagnaceae).  Also found are the various species of Lilaeopsis and Hydrocotyle (Apiaceae), Oritrophium peruvianum (Asteraceae), Plagiobothrys linifolius (Boraginaceae), Draba lindenii (Brassicaceae), Stellaria media (Caryophyllaceae), Halenia spp. (Gentianaceae), Myriophyllum quitense (Haloragaceae), Juncus spp. (Juncaceae), Huperzia spp. (Lycopodiacee),  Rumex tolimensis (Polygonaceae) to 4-5 m tall, Caltha sagittata and Ranunculus praemorsus (Ranunculaceae), and Mimulus glabratus and Pedicularis incurva (Scrophulariaceae).  Shallow pool, lake, and river communities (Figs. 15C-D) include Callitriche spp. (Callitrichaceae), Elatine spp. (Elatinaceae), Myriophyllum spp. (Haloragaceae), Isoëtes spp. (Isoetaceae), Cortaderia spp. (Poaceae), Potamogeton spp. (Potamogetonaceae), and Ranunculus spp.
      Rock ledge and cliff communities harbor another distinct group of interesting plants including Draba spp. (Brassicaceae), Luzula racemosa (Cyperaceae), Escallonia myrtilloides and Ribes hirtum (Grossulariaceae), Calceolaria spp. (Scrophulariaceae) and numerous fern species in the genera Asplenium and Cystopteris (Aspleniaceae) and Elaphoglossum and Woodsia (Dryopteridaceae).
      Trees of the genus Polylepis (Rosaceae), with their characteristic reddish, exfoliating bark and strangely contorted trunks and branches, may form localized, isolated woodlands or forest communities to over 4000 m elevation within otherwise grass páramo. They are often found on scree slopes, near the shelter of rock cliffs, or in river valleys. It is interesting that within the Polylepis forest there is a noticeable drop in plant diversity compared to the surrounding grass páramo (páramo species are probably shade intolerant), and furthermore that certain plants grow only under Polylepis. Polylepis forest is still relatively underexplored and an overall study of its flora would be very interesting (but see Arnal, 1983;  Fjeldså and Kessler, 1996;  and Hueck, 1960a).

Lupinus

Eryngium humile

Halenia spp.

      Subpáramo.  The lowest zone, called subpáramo, is also the most diverse and floristically showy.  It is a shrub-dominated transition zone at (2800-)3000-3500 m elevation made up of elements from forest below and the grass páramo above. It is often a mosaic of shrubs and small scattered trees, gradually reduced in size, giving way to scrub and low vegetation of dwarf shrubs, grasses, and herbs of the grass páramo above. Sometimes local changes in topography and soils may give way to different microclimatic conditions and so small patches of forest may be present. Where the ecotone between forest and páramo is abrupt, or where isolated shrub-tree islands are found within páramo, it is usually brought about by anthropogenic means, especially cutting, burning, and grazing.  Therefore, it is possible that subpáramo consists of nearly all secondary communities.
      The subpáramo communities, often known as scrub, thickets, "chaparrales"  or "mattorales", are composed predominantly of shrubby or woody vegetation that is sometimes lacking or rare in the Andean forest below.  These include species of the genera Ilex (Aquifoliaceae), Ageratina, Baccharis, Chuquiraga, Diplostephium, Gynoxys, Loricaria, Senecio and Stevia (Asteraceae), Berberis (Berberidaceae), Siphocampylus (Campanulaceae-Lobelioideae), Hypericum (Clusiaceae), Coriaria (Coriariaceae), Desfontainia (Desfontainiaceae), Bejaria, Cavendishia, Gaultheria, Macleania, Pernettya, Semiramisia, Themistoclesia and Vaccinium (Ericaceae), Brachyotum, Chaetolepis, Miconia and Monochaetum (Melastomataceae), Myrsine (Myrsinaceae), Monnina (Polygalaceae), Rubus (Rosaceae), Arcytophyllum (Rubiaceae), Aragoa and Calceolaria (Scrophulariaceae), Symplocos (Symplocaceae), and Ternstroemia (Theaceae).  Woody epiphytes in the Ericaceae (e.g., Disterigma, Plutarchia, Sphyrospermum, Thibaudia) and Loranthaceae (e.g., Aetanthus) (Figs. 10D and 14B) are also common.
      Genera forming low forests of small trees up to eight meters tall, often in tree islands known as "bosques achaparrados" include:  Oreopanax and Schefflera (Araliaceae), Gynoxys, Diplostephium and Senecio (Asteraceae), Buddleja (Buddlejaceae), Weinmannia (Cunoniaceae), Bejaria (Ericaceae), Escallonia (Grossulariaceae), Miconia (Melastomataceae), Myrsine (Myrsinaceae), and Hesperomeles (Rosaceae).
      Subpáramo has many common names, of which the most frequently used are: páramo forest, páramo thicket, shrubby páramo, subpáramo woodland, subpáramo chaparral, subpáramo elfin forest, and tropical subalpine forest (in English);  paramillo, paramito, bosquecillo de páramo, matorral de páramo, matorral de subpáramo, bosque paramero, bosque subparamero, bosque enano, bosque musgoso de subpáramo, bosquete andino, and chirivital (in Venezuela) (in Spanish);  and paramillo thicket and paramillo scrub (mixed Spanish and English).
      In general terms, subpáramo is the most difficult of the three páramo zones to define, because it has been greatly extended and expanded both horizontally and vertically (downwards) by human disturbance and habitat destruction over hundreds, or perhaps thousands of years.  This is especially due to cutting and burning at the upper forest line for herding and agricultural purposes.  Correspondingly, forest lines appear to have been lowered by as much as several hundred meters by human interference (Lægaard, 1992), and many species that were more restricted to relatively high elevations appear to have colonized lower life zones (Budowski, 1968).  Much of both subpáramo (non-controversial) and grass páramo (somewhat controversial) now occur in areas that were probably covered with upper montane forests in the past (Lægaard, 1992).

      Detailed classifications of páramo vegetation have been constructed utilizing relevés in the Zürich-Montpellier approach and described following the international "Code of Phytosociological Nomenclature" (Barkman et al., 1976).  This system divides vegetation into units or communities on the basis of floristic, physiognomic, and ecologic similarities, and usually employs a detailed classification of the vegetation consisting of a syntaxonomical hierarchy (subassociation, association, alliance, order, class, etc.).  For further explanation of this methodology, see R. Becking (1957), Braun-Blanquet (1964), Mueller-Dombois and Ellenberg (1974), and Westhoff and Van der Maarel (1973).  For applied examples of this methodology, with lists of species characterizing the various plant communities, see Aguirre and Rangel Ch. (1976), Cleef (1981b, including figs. 11-79), Franco R. et al. (1986), Lozano C. and Schnetter (1976), Sturm and Rangel Ch. (1985, including figs. 4-7), and Vargas Ríos and Zuluaga (1980).  Páramo studies using other quantitative methods may be seen in Baruch (1984) and Fariñas and Monasterio (1980) for Venezuela, and in Balslev and de Vries (1982), Grubb et al. (Unpublished), Muñoz et al. (1985), and Ramsay (1992) for Ecuador.

Gynoxys miniphylla

Monnina crassifolia

Rubus coriaceus

Morphological and Physiological Adaptations

      Since páramo is a high elevation tropical ecosystem, certain characteristic physical, chemical, and climatic features affect the biological functioning of the organisms that live there.  Therefore, the plants that grow in these areas must be adapted to:   1) high elevation air (with less water content and lower partial pressures of gasses such as O2 and CO2),  2) low temperatures (in the shade the annual mean temperature decreases about 0.6°C for each 100 meters increase in elevation, whereas in full sunlight, it increases with elevation because the atmosphere neither absorbs nor disperses as much radiation energy as in the lower regions),  3) intense ultra-violet radiation (highest in equatorial high mountains, but controlled by frequent fog and cloud cover), 4) rapid changes in insolation resulting in quick absorption or loss of heat,  5) drying effect of winds (by increasing transpiration to the point of desiccation), 6) physiological dryness (due to the combination of low temperatures, intense transpiration during sunny periods, and drying effects of winds, along with high soil acidity and high osmotic pressure of soil water making root water-absorption difficult), and 7)  physical damage from hail and possibly snow (Acosta-Solís, 1984;  Cleef, 1981b;  Cuatrecasas, 1968;  Little, 1981;  Mani, 1980;  G. Sarmiento, 1986;  A. P. Smith, 1981;  Vareschi, 1970;  Young, pers. comm.).  Consequently, growth and decomposition are slow, primary productivity is low, and natural succession of the vegetation takes a long time, especially when woody species are involved (Ferweda, 1987;  Hofstede, 1995c;  Horn, 1989, 1997;  Janzen, 1973;  Ramsay & Oxley, 1996;  Salamanca V., 1991;  L. Sarmiento M. et al., 1990;  A. P. Smith, 1981;  Sturm, 1978;  Williamson et al., 1986).  It is important to remember that there is no strong temperature seasonality, no marked change from summer to winter as in the temperate regions, but that in páramo growth is continuous throughout the year and that great changes in temperature (and to a certain extent precipitation) occur every day (diurnally).  Smith and Young (1987) noted that "Many aspects of morphology and physiology seem to provide escape from, or tolerance to, extreme diurnal climatic fluctuations."
      Recent studies have shown how giant Andean rosettes (e.g., Espeletia and Puya), have evolved adaptations that favor temperature insulation and the maintenance of a positive water balance under the severe conditions of the páramo environment.  Adaptations to low temperatures include freezing avoidance mechanisms such as supercooling of adult leaves (Goldstein, Rada & Azócar, 1985;  Larcher, 1975;  Rada R. et al. 1985a);  insulation by retention of dead leaves (marcescent leaves), which protects rosette stems from freezing (Goldstein & Meinzer, 1983;  Rada R. et al., 1985a;  A. P. Smith, 1979);  parabolic leaf geometry and nyctinastic movements of the leaves, which result in protection of the apical leaf bud from freezing (O. Hedberg, 1964;  Larcher, 1975;  A. P. Smith, 1974b);  thermal buffering by mucilaginous fluids secreted by the leaf bases, which protect apical buds (Smith & Young, 1987);  dense leaf pubescence, which reduces transpiration (Baruch, 1972) and increases leaf temperature (Baruch, 1975;  Meinzer & Goldstein, 1985;  Meinzer, Goldstein & Rada, 1994;  Miller, 1986, 1994);  tall aerial stems, which protect buds against the low minimum nighttime temperatures at ground level (Meinzer, Goldstein & Rada, 1994;  A. P. Smith, 1980);  and contractile roots in juvenile plants, which draw the developing stem into the ground (Smith in Smith & Young 1987).
      Rosette adaptations to low moisture levels include changes in the method of CO2 assimilation, such as a switch to the CAM photosynthetic pathway (Baruch & Smith, 1979;  Medina, 1974);  and a well-developed water-storing pith tissue, which can be used particularly during early morning hours when cold or frozen soils limit water uptake during that period of high transpiration (Goldstein & Meinzer, 1983;  Goldstein et al. 1984;  Meinzer & Goldstein, 1986;  Meinzer, Goldstein & Rundel, 1994;  Meinzer et al. 1985).  Some rosette plants, like Draba chionophila (Brassicaceae), which grows up to ca. 4800 m in the Venezuelan Andes, are freeze-tolerant (i.e., freezing injury occurs only when temperatures drop below the temperature at which extracellular ice formation begins) (Azócar et al., 1988;  Goldstein et al., 1994;  Pfitsch, 1994).  For reviews of general adaptive radiation in Espeletia and other plants of the high Andes, see also Beck (1994), Goldstein et al. (1994), Hedberg and Hedberg (1979), Monasterio (1986b), Monasterio and Sarmiento (1991), Ramsay (1992), Rundel et al. (1994), and Smith and Young (1987).
      Some of the physiological and morphological adaptations discussed above work in combination, that is, not only as avoidance/tolerance mechanisms against a cold environment, but also as useful adaptations against a hot environment resulting from frequent fires. Adaptations to high elevation by páramo plants result in the characteristic growth forms discussed below.

Growth Forms

Hypochaeris

Chuquiraga

Disterigma

      Most high elevation tropical plant communities have a characteristic physiognomy, which repeats in geographically disjunct areas of the world where they occur, for example, South America, East Africa, and Hawaii (Cuatrecasas, 1968;  O. Hedberg, 1964, 1992;  Hedberg & Hedberg, 1979;  Raunkiaer, 1934;  Troll, 1958;  Vareschi, 1970).  The growth forms (sensu lato) that characterize this physiognomy are examples of convergent evolution, the forms having evolved independently in several different plant families on distant continents in response to the unique high altitude tropical environments.  These growth forms often result from the ecological and morphological adaptations mentioned above.  Many are also apparantly adapted to survive fire (Lægaard, 1992;  Young & León, 1991). 
      While the tree is the dominant growth form in the forest, it is essentially absent from páramo (except the genus Polylepis and a few associated species).  Apparently it cannot survive at such altitudes.  In fact, tree growth ceases when soil tempertures drop to 6-10°C (Larcher, 1975;  Lauer, 1979a, 1981;  Walter & Medina, 1969a,b).  Páramo, however, has its own important and conspicuous growth forms (not all of which are strictly found in páramo), such as bunchgrasses, rosettes plants, cushion plants, microphyllous and dwarf shrubs, vagrant plants, and geophytes.  The presence of rosette plants (some of giant size), for example, is probably a good general indicator of páramo and seems to be one of the clearest distinctions between high elevation areas of tropical and temperate latitudes (A. P. Smith, 1994).  The most characteristic growth forms of the high elevation páramos are summarized below.  See also Balslev and de Vries (1991), O. Hedberg (1964, for comparisons with Afroalpine plants), Hedberg and Hedberg (1979), and Ramsay and Oxley (1997).

      Rosette Plants.  This growth form gives páramo vegetation its distinctive character. Two kinds of rosette plants have been described:
      Stem rosette.--  The most typical and well known growth form of páramo is the columnar woolly rosette plant.  Members of the genus Espeletia (Asteraceae), the so-called "frailejón" (or literally translated "big friar") because of the grayish woolly coat of pubescence, are the classical example.  These plants produce an erect, normally unbranched, thick-woody stem tightly encased by the dense bases of old leaves (Cuatrecasas, 1968).  The erect stems may be as tall as 15 meters in undisturbed páramo. Lateral inflorescences are produced from the single aerial meristem. Other examples of this growth form are the fern Blechnum schomburkii (Blechnaceae) and Plantago sericea ssp. perrymondii (Plantaginaceae). It has been shown that woolliness is a response to ultra-violet light and is associated with thermoregulation, the retarding of evaporation, and general protection from UV light (Miller, 1994).
      Acaulescent rosette.--  These plants develop thick, perennial, tap-roots and a dense rosette of leaves at the ground level.  The flowering stems may be very short with the flowers hidden in and amongst the leaf bases, or longer thereby lifting the flowers above the ground surface.  Some plants, such as Puya spp. (Bromeliaceae), produce giant, bulky inflorescences several meters tall. In all cases, the buds that form the flowers originate in the axils of the rosette leaves, which are sunken a few centimeters below the ground.  Acaulescent plants thereby protect their buds from fire and frost.  Experiments have shown that the mean temperature within the rosette is higher (by about 6°C) than in the surrounding air (Hedberg & Hedberg, 1979), and that these plants seem to buffer temperature variations to such an extent that they are able to avoid both positive and negative extremes (Goebel, 1891;  O. Hedberg, 1964).  Examples are shown by the genera Hypochaeris and Werneria (Asteraceae), Lysipomia (Campanulaceae-Lobelioideae), Paepalanthus (Eriocaulaceae), Lupinus alopecuroides (Fabaceae), Acaulimalva and Nototriche (Malvaceae), Rumex tolimensis (Polygonaceae), Ranunculus gusmanni (Ranunculaceae), Acaena cylindristachya (Rosaceae), Valeriana plantaginea (Valerianaceae), and Viola (Violaceae).

      Cushion Plants.  These plants form a flat, convex, or hemispherical cushion as the result of the regular outward branching of dense radially oriented buds. Each branch has a small rosette of leaves at the tip and only the outer and upper leaves are green and living;  the interior of the cushion consists of a peaty mass, the remains of dried leaves, accumulated humus, dust, soil, and rain water, all of which protect the buds and stems from wind, desiccation and predation, and provide a reservoir of water and nutrients (Sklenár, 1998).  Like in rosette plants, the mean temperature is higher within the cushion than at the cushion surface, thereby protecting the buds from cold temperatures.  The plants are often very prickly and hard to the touch, yet firm enough that one is able to walk on top of certain species, such as in Azorella (Apiaceae), Plantago (Plantaginaceae) (Figs. 9C and 19), and Distichia (Juncaceae). Many different species, in different families, form cushions of different sizes, from flat or only a few centimeters tall to cushions over one meter tall and several meters in diameter, for example Azorella pedunculata.  In moist or humid sites, where cushions are more frequently found, Distichia muscoides and Plantago rigida are dominant species, while in drier places Azorella pedunculata and A. aretioides are common. Other genera that produce cushions include Werneria pygmaea and Xenophyllum spp. (Asteraceae), Draba aretioides (Brassicaceae), Arenaria spp. (Caryophyllaceae), Oreobolus spp. (Cyperaceae), Disterigma empetrifolium and Pernettya prostrata (Ericaceae), Paepalanthus lodiculoides (Eriocaulaceae), Geranium spp. (Geraniaceae), Aciachne pulvinata (Poaceae), Calandrinia acaulis (Portulacaceae), Valeriana rigida (Valerianaceae), and Xyris subulata (Xyridaceae). See O. Hedberg (1964, 1992), Heilborn (1925), Sklená_ (1998), and Rauh (1939) for extensive discussions of morphology and adaptation of cushion plants to high elevation environments.

      Bunchgrasses (or Tussock Grasses).  This growth form is the most widespread in the páramo.  In undisturbed areas, grasses may average 1-1.5 m tall with a coverage of up to 100%.  Members of the grass and sedge families frequently form tufts or dense bunches of stems (culms) with rigid, pointed, tubular or inrolled leaves. These dense tufts in which the dead leaves are maintained and decay on the plant, along with the culms, provide good insulation for the buds and young leaves from cold temperatures, high radiation, evaporation, and high heat of fires to 500°C (Ramsay, 1992;  Ramsay & Oxley, 1996).  Much of their regeneration takes place through the production of vegetative buds near the ground.  Here the tufts are very dense and living shoots are found along with dead culms and leaves.  These tufts protect the vegetative buds.  The most common species are Calamagrostis recta and C. effusa (Poaceae); other important genera and species are Carex and Uncinia (Cyperaceae), Cortaderia spp., Festuca dolichophylla, F. tolucensis, Stipa spp., and Lorenzochloa erectifolia (Poaceae).  See Hofstede (1995c), Ramsay (1992), and Ramsay and Oxley (1997) for additional discussion of how the bunchgrass growth form is an adaptation to fire in the páramo environment.

      Microphyllous Shrubs.  These shrubs are characterized by dense foliage of small, xeromorphic leaves, sometimes with many of the following combinations of adaptations in the same species, all acting as protection from ultraviolet light and/or the reduction of transpiration (O. Hedberg, 1964;  Larcher, 1975).  Examples of genera and/or species with hard or sclerophyllous leaves include Gaultheria anastomosans and Gaylussacia buxifolia (Ericaceae), and Miconia summa (Melastomataceae);  squamous or rolled leaves Baccharis revoluta and Diplostephium revolutum (Asteraceae), and Miconia salicifolia (Melastomataceae);  imbricate leaves Loricaria (Asteraceae) and Aragoa cupressina (Scrophulariaceae);  aciculate or spine-tipped leaves Chuquiraga (Asteraceae), Hypericum laricifolium (Clusiaceae), and Valeriana microphylla (Valerianaceae);  and densely tomentose-pubescent leaves Diplostephium eriophorum and Pentacalia guicanensis (Asteraceae), and Gaultheria lanigera (Ericaceae).
      The so-called bouquet plants ("plantas en ramilletes de florones") are a subset of microphyllous shrubs with a special habit.  These plants feature an increase in the size of an individual flower in relation to the total appearance of the plant (e.g., Bidens humilis), or the dense aggregation of many small flowers into a bouquet of dense flowering stalks (Vareschi, 1970).  This is considered an adaptation to make the flowers more attractive to pollinators by forming a large and noticeable splash of color that attracts insects from a distance, as in species of Draba (Brassicaceae), Gentianella (Gentianaceae), and Chaetolepis (Melastomataceae).

      Prostrate Dwarf Shrubs.  These are small, woody plants that rarely produce shoots over 0.75 m tall.  The special feature separating them from microphyllous shrubs is that they have a larger part of their branch system protected below or upon the soil surface.  They are often prostrate, growing laterally along the ground.  Sometimes entire branching systems occur underground and only the current year's growth is seen above ground.  This growth form often has its regenerative buds below ground where they are protected from fire and frost.  Examples are found in Bidens and Senecio (s.l.) (Asteraceae), Lupinus and Astragalus (Fabaceae), Pernettya and Disterigma (Ericaceae), and Arcytophyllum (Rubiaceae).

      Geophytes.  These are herbs that survive the unfavorable periods of the year (including times of fire) by means of subterranean organs, such as succulent roots, rhizomes, stolons, tubercules, or bulbs (Lægaard, 1992;  Raunkiaer, 1934;  Vareschi, 1970).  Examples of geophytes include Orthrosanthus chimboracensis (Iridaceae), the genus Stenomesson (Amaryllidaceae), Altensteinia and Gomphychis (Orchidaceae), and the fern Ophioglossum crotalophoroides (Ophioglossaceae).

      Vagrant Plants.  These plants grow free, unattached to the substrate, and are found in many biomes throughout the world (Pérez, 1994a, 1997b).  They are found in the superpáramo zone, where frost-heaving is a common phenomenon, and only in cryptogamic plants such as the fruticose lichen Thamnolia vermicularis (family uncertain) and an acrocarpous moss Grimmia longirostris (Grimmiaceae).  These plants have been variously referred to as erratic, vagant, vagrant, solifluction floaters, errant cryptogams, and sometimes globular mosses or moss balls when their growth shape becomes more spherical (see Pérez, 1997b for more details).  Cryptogams as a whole (i.e., bryophytes and lichens) have been considered a true growth form by Cuatrecasas (1968), Griffin (1979), and Ramsay (1992), or as composed of several growth forms by Ramsay and Oxley (1997).

Flora

      On a geological timescale the páramo flora is young, the so-called protopáramo vegetation of Van der Hammen and Cleef (1986) having evolved during the Late Pliocene or Early Pleistocene, some 2-4 Ma.  Páramo environments suitable for plant colonization on an extensive scale, however, have only been available since the Quaternary (Simpson, 1975;  Van der Hammen, 1974;  Van der Hammen & Cleef, 1986).  The youth of the páramo flora is also evidenced by the presence of relatively few endemic or near endemic genera (23 genera, ca. 5% based on this work) and the absence of any endemic families in the vascular flora.  Although the páramo ecosystem occupies no more than 2% of the land area of the countries in which it is found, the flora is extremely diverse.  In fact, the páramo flora is the richest high mountain flora of the world (Smith & Cleef, 1988).  The páramo flora has evolved in various ways:  by adaptation of lower elevation plants (i.e., tropical elements) to high elevation environments, by immigration (i.e., dispersal) of cool-adapted plants from north and south temperate regions, and by speciation through isolation from within (i.e., autochthonous element).  For discussion of these and other ideas, see Chapman (1917), Chardon (1938), Simpson (1975), Simpson and Todzia (1990), Van der Hammen (1972a,b), and F. Vuilleumier (1970).