Vagant cryptogams in a paramo of the high Venezuelan Andes

Flora (1994) 189 263-276 © by Gustav Fischer Verlag Jena

Vag ant cryptogams in a paramo of the high Venezuelan Andes FRANCISCO L. PEREZ Department of Geography, University of Texas, Austin, Texas, 78712-1098, USA Accepted: March 15, 1994

Summary Five types of vagant cryptogams are found in the high-elevation areas of the Paramo de Piedras Blancas, in the northern (Venezuelan) Andes. Unattached, free-growing specimens of the lichens Thamnolia vermicularis (Sw.) ACH. ex SCHAERER and Xanthoparmelia vagans (NYLANDER) HALE are blown about by the wind. T. vermicularis is the most common vagant plant of this paramo, where it is nearly ubiquitous. Populations of X. vagan~ are more restricted, and have been found only above 4375 m. Small spheroidal masses of soil covered by the lichen Catapyrenium lachneum (ACH.) R. SANTESSON or the moss Grimmia longirostris HOOK. are disturbed and transported by soil-frost activity (needle ice) aided by gravitational descent. Only one sizable population of C. lachneum globoids was located at 4540 m, while several populations of moss balls of G. longirostris were found between 4290 and 4570 m. Small soil buds and nubbins, common on the ground surface of the high paramo, are often covered by an unidentified species of Marsupella (Hepaticae). A few vagant globular specimens of this liverwort containing soil inclusions were found at 4540 m; these were probably detached from the ground surface by frost activity. This diverse community of erratic cryptogams is the first to be ever described for the Andean cordillera. Key-words: Vagant cryptogams, erratic lichens, mosses, Paramo, Andes, Venezuela

1. Introduction 'Vagant' plant life-forms (WEBER 1977), growing free without any attachment to the substrate, are found in many biomes all over the world. A number of plants, commonly cryptogams, have adopted this unusual habit; they have been described in the literature as 'errant cryptogams' (CLEEF 1981), 'solifluction floaters' (HEDBERG 1964), and 'plantas edaJojlotantes' HALLOY 1983). Loose-lying lichens are particularly numerous, and the terms 'erratic thalli' (ROGERS 1977), 'free-growing lichens' (HALE 1990), 'licheni vaganti' (PICHI-SERMOLLI 1938), 'aerolichenes' or 'Wanderjlechten' (MATTICK 1951), and 'liquenes migratorios' (FOLLMANN 1966) have been applied to them. Over 60 lichen species worldwide, primarily from the genera Xanthoparmelia and Aspicilia, display this growth form (PEREZ unpubl. data). Unattached mosses are fairly common in cold regions of the world, and are most often called moss 'balls' or 'globoids' (LID 1938, BECK et al. 1986). About 34 moss species, mainly from the genera Grimmia,

Racomitrium, and Andreaea, have developed the vagant habit (PEREZ 1991 a). Erratic forms appear to be rare in macroscopic plants other than lichens and mosses. At least one terrestrial alga (Nostoc commune) produces small circular patches which lie loose on the soil surface of the Afroalpine zone of Mt. Kenya (HEDBERG 1964: 69). Nostoc often also builds vagant balls similar to those of mosses (JOSEF POELT, 1993, pers. comm.). HAL LOY (1983: 119) reports that popUlations of two normally rooted species of phanerogams, a small composite (Chaetanthera spp.) and a Gramineae (Hordeum halophilum) , also include some healthy unattached specimens in the high NW Argentinian Andes. Hepaticae are also able to produce vag ant forms in aquatic environments; this is the case of Jungermannia pallida, which forms small spheroidal masses along sulphureous streams of Japan (HORIKAW A 1960). The habit of this liverwort is comparable to that of some marine algae and aquatic monocotyledons, such as Posidonia oceanica, which are shaped into small balls as plant material is detached and FLORA (1994) 189

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rolled by the force of waves and currents (AUBERT DE called jalcas. The Paramo de Piedras Blancas occupies an extreme northern location along the LA RUE 1968). Andean cordillera, in the Sierra de La Culata, Vagant cryptogams are found primarily in warm deserts, high-latitude steppes and tundras, and high- southeast of Lake Maracaibo. The area of study is altitude ('alpine') areas. Initial plant detachment from located between about 8° 50' and 8° 54' N latitude, the substrate can be accomplished by rain erosion 70° 51' and 70° 54' W longitude, and extends ap(HARRIS 1901), wind (ASHTON & GILL 1965), frost and proximately between 3700 and 4700 m elevation needle ice (HEDBERG 1964), and animal disturbance or (Fig.1.). This high paramo has a semiarid [paramo human treading (BURRELL 1907). Dispersal, especially deserticoJ and cold periglacial climate. Yearly in deserts and steppes, is effected mainly by wind (SMITH precipitation is low, slightly over 800 mm. Two 1921, FOLLMANN 1966, WEBER 1977). Raindrop impact distinct seasons occur: ~ 70% of the annual mean can also turn over loose plants (MEREWSCHKOWSKY falls during the rainy period, from May to August, 1918), and running water may transport them (GREM- while the driest season, from December to March, MEN 1982). In tundras and alpine areas, frost activity gets only about 10% of the total (PEREZ 1991 b). and solifluction, particularly in relation with needle-ice Temperatures above 4000 m dip below freezing formation, are also efficient agents of transport for nearly every night, specially during the dry season, erratic plants (HEDBERG 1964, CLEEF 1981, BECK et al. when minima as low as -12.2 DC can be reached; 1986). Soil instability due to freezing and thawing can 325 to 350 air freeze/thaw cycles occur each year in be so extreme in some periglacial regions, that ThOLL this area. This high frost recurrence causes fre(1944) called them 'mobilideserta', and HEDBERG (1964) quent formation of needle ice, which is widespread used the term 'solifluction floater' to designate vagant during the rainy season when soils are saturated, life forms there. Gravitational transport obviously also but restricted to a few moist locations during contributes to the descent of erratic plants on slopes, as is the case with globular mosses, often concentrated below the rock outcrops which act as sources of the fragments that become moss balls (PEREZ 1991 a). Reports of vagant plants are scarce for south America.FoLLMANN (1966, 1967) has published detailed accounts of erratic lichens for the fog oases in the coastal deserts of northern Chile, while THOMSON & ILTIS (1968) described similar communities for the nearby deserts of southern Peru. No specific studies of vagant cryptogams have been published for the South American Andes, although CLEEF (1981: 78) mentioned the presence of three species of errant mosses, and of two species of erratic lichens, in the high paramos of the eastern Colombian cordillera. Similar tropical-alpine environments in east Africa, such as Mts. Kenya and Kilimanjaro (ThOLL 1944, HEDBERG 1964, BECK et al. 1986) and the Semien • mountains of N. Ethiopia (PICHI-SERMOLLI 1938), also have vagant plant populations. The purposes of this study are to present an account of the different types of erratic cryptogams found in the Paramo de Fig. 1. A. Location of the Venezuelan Andes (dark stipPiedras Blancas, an equatorial high-altitude area of pled area). B. Generalized topographic map of the Venethe Venezuelan andes, and to summarize and evalua- zuelan Andes; contour interval is 1000 m. The Sierra de La te the available information on the distribution and Culata is the stippled area southeast of Lake Maracaibo; only the zone above 3000 m, which corresponds approxiecology of these specific vagant life-forms.

2. The Study Area The paramos are the alpine-equivalent regions of the tropical Andes. They are mainly found in Venezuela, Colombia, and Ecuador; in northern Peru, they are 264

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mately with the paramos, has been shaded. The study area (Paramo de Piedras Blancas) is shown by a dark triangle. Rivers are shown by a thin dash/dot line. The international boundary with Colombia is shown by a thick dashed line. Dots indicate major cities. Key: SC: San Cristobal; T: Tovar; M: Merida; MU: Mucuchies; SO: Santo Domingo; TR: Trujillo; B: Bocono.

Fig. 2. View of a summit plateau at 4545 meters, below Pico Los Nevados; the base of this peak appears in the background. Specimens of all the vagant organisms discussed in the paper were found on this plateau. The ground surface is totally covered by a characteristic irregular, puffy soil texture (nubbins and soil buds) produced by needle-ice disturbance; note the total lack of vascular plant cover on the plateau. The granitic block in the middle ground is about 1.6 m tall. Dec. 1985.

the dry season. Many types of patterned ground formed by frost and needle ice are found in the paramo (PEREZ 1987, 1992a), particularly at the highest elevations, where vag ant cryptogams are also more common. The most frequent soil patterns are 'nubbins' and 'fine-soil buds' WASHBURN 1973: 82), small round to elongate earth lumps, a few cm in diameter, found at the ground surface (Fig. 2).

3. Types of vag ant cryptogams in Piedras Blancas Five different types of cryptogams (three lichens, a moss, and a hepatic) were found to produce vagant forms in the high Paramo de Piedras Blancas. Most sites inspected had two or more vag ant types lying next to each other. The cryptogams were normally found separately, i.e., individual erratic specimens consisted of a single species. However, in a few cases, species were intermixed in the same loose mass. These vagant cryptogams are discussed below individually.

3.1. Thamnolia vermicularis (Sw.) ACR. ex SCRAERER Thamnolia is a common cosmopolitan genus of fruticose lichens, found in arctic and alpine areas of all continents except Africa and Antarctica (SHEARD 1977). Thamnolia was first collected by SWARTZ in 1781, in Lapland (CULBERSON 1963). There are two species, T. vermicularis (Sw.) ACH. ex SCHAERER and T. subuliformis (EHRH.) W. CULB. These are morphologically identical, but can be easily separated on the basis of their chemical composition (ASAHINA 1937) and fluorescence under UV light (SATO 1963). In addition, both species have solid and hollow forms (SATO 1968, WEBER 1992, pers. comm.). T. subuliformis is more common in the northern hemisphere, while T. vermicularis is more abundant in southern continents. In South America, T. vermicular is has been reported for Tierra del Fuego (Chile), the high Andes of Peru, and the Ecuadorian, Colombian, and Venezuelan paramos (VARESCHI 1953, 1970, SATO 1968, CLEEF 1981). In contrast, T. subuliformis has only been found in one Peruvian locality (SATO 1968). T. vermicularis is the only vagant lichen previously described for the Venezuelan Andes, where it is FLORA (1994) 189

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Fig. 3. Representative specimens of Thamnolia vermicularis (Sw.) ACH. ex SCHAERER, collected at 4 380 m elevation. Note the hollow thallus tube of the lichen on the lower right. Scale is in em (black and white segments) and mm.

widely distributed above 3500 m or so (VARESCHI 1953). I have collected and examined ~ 900 specimens from several micro-localities (SATO 1963) above 4200 m in Piedras Blancas. Specimens were always hollow; examination under UV light (3,500 A) showed that only the insides of some thallus tubes were faintly fluorescent (cf. FILSON 1972), but all the outer thalli surfaces were UV-negative. Therefore, all the lichens inspected were T. vermicularis and the ratio mixture (SATO 1963) of Thamnolia species for this Venezuelan paramo is given as 100:0. Specimens from Piedras Blancas have thalli which are cream white to greyish-white (lOYR 8/2 1), thin (1 to 4 mm), short (usually 2 to 5 cm), curved or elongated smooth cylindrical tubes, generally pointed at the growing end but fragmented and apparently dying at the other end, and are usually found as single unbranched or slightly branched strands (Fig. 3). Because of their small size and hollowness, individual thalli are very light; the largest (dry) lichen at each micro-locality weighed only 0.05 to 0.15 g. Total lichen biomass on level surfaces, as sampled on six 228 cm 2 micro-plots, varied from 13.3 to 42.6 g/m 2 (mean: 27.2 g/m 2). However, Thamnolia often becomes concentrated in small hollows and low-lying depressions (PEREZ 1991 c), where it can attain a high biomass, of up to 300 g/m2. Lichen concentration 1) Colors are given also with the notation of the Munsell Soil Color charts (1975 edition).

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may have occurred due to wind (WEBER 1977: 23), rain (RICHARDSON & YOUNG 1977: 136), needle ice, and/or gravity. Similar accumulations of other vagant lichens have been observed by PICHI-SERMOLLI (1938) and TROLL (1944) on the depressed edges of small soil polygons of several high East African mountains. All the thalli examined were sterile, lacking any apothecia or pycnidia (CULBERSON 1963). VARESCHI (1970: 79) described 'pseudo-apothecia' in specimens from a nearby paramo, but it is likely that this report, like others elsewhere, was based on lichen parasites (WEBER & SHUSHAN 1955, THOMSON 1984). In fact, Thamnolia reproduces worldwide solely by thallus fragmentation (SHEARD 1977); therefore, this genus remains in the 'Lichenes Imperfecti'. Thamnolia is a taxon of great antiquity, as it dates back to the Permian-Triassic (SHEARD 1977). The fact that Thamnolia is absent from recent, active volcanoes (SATO 1965) suggests that long-distance dispersal took place in ancient times but is not presently occurring (THOMSON 1984). Thamnolia thalli in Piedras Blancas were always vagant and unattached to the substrate, which consisted usually of bare soil affected by needle ice. Lichens were also often found on turf-covered areas and on isolated plant cushions of Aciachne pulvinata BENTH., Arenaria musciformis PL. & TRIAN., Azorellajulianii MATH., Lucilia venezuelensis STMK., and Werneria pygmaea GILL. This, coupled to the lightness of the

thalli, suggests that T vermicularis is primarily distributed by aeolian activity in the paramo, as only wind could carry the lichens onto the convex, domed surfaces of cushion plants. A literature review indicates that Thamnolia commonly behaves as vagant, but it can also be found firmly attached to soil (MARTIN & CHILD 1972) and a variety of substrates, including mosses (VARESCHI 1970), bare rock blocks (WEBER 1992, pers. comm.), and even animal droppings (SMITH 1921: 378). Thus, Thamnolia should be considered only as a 'facultative' vag ant cryptogam. It is noteworthy that the Andean peasants are well acquainted with T vermicularis, and use it, as a depurative, for medicinal purposes (VARESCHI 1970).

3.2. Xanthoparmelia vagans (NYLANDER) HALE.

Xanthoparmelia, with 406 species, is an important genus within the foliose Parmeliaceae family; at least 25 species are classified as vag ant forms (HALE 1990). Xanthoparmelia vagans (NYLANDER) HALE was first collected by A. BONPLAND in Ecuador on Chimborazo, during his historic ascent with A. VON HUMBOLDT to this massive volcano in 1802; the species was then classified by NYLANDER in 1858. X. vagans is restricted to the Americas. In North America, it is found in the western USA (HALE 1990) and in Mexico, in the mountains near Puebla (GYELNIK 1938). Even though the type for X. vagans came from the North Andean paramos, I could find no further references to this lichen for the equatorial Andes; apparently my collection in Jan. 1992 is the second one from this region. In South America, X. vagans has also been reported from the humid Peruvian jalcas (DIX 1952) and for the Atacama desert of Chile (FOLLMANN 1966). It is probably also found in Argentina, since GRASSI (1950) reports 'x. camtschadalis' for the southern Andes. However, this last species is strictly Holarctic, and the taxonomic literature is riddled with incorrect mentions of, among others, the epithets vagans and camtschadalis (see HALE 1990). X. vagans specimens are always found in erratic form, and pycnidia and apothecia are absent from them. Therefore, this lichen is classified as an 'obligatory' erratic species (FOLLMANN 1966). Two sizable populations of X. vagans were found at 4375 and 4530 m altitude. Specimens were collected from the highest- and densest-population, located at the edge of a small plateau below Pico Los Nevados, one of the highest peaks of the Sierra La Culata (see Fig. 2). Several hundred individuals occupied a few tens ofm 2 on a gentle (13 -15°), exposed, SSE-facing slope which was nearly devoid of vascular plant

cover; only a few small clumps of Agrostis breviculmis HICHC. and cushions of Arenaria musciformis were present nearby. T vermicularis was also found there in abundance. The bare ground surface was totally covered by fresh, moist nubbins, over which the loose lichens rested. A total of 166 specimens was collected from an area of about 2 m 2. Most thalli clearly had an 'upper' and a 'lower' side, which differed in coloration, but several lichens showed no difference between either side. Presumably, the former lichens had remained in the position I found them for an extended period of time, while the latter had been more frequently overturned. The upper surface of the lichens had a pale yellowish green (5Y 8/4) to olive gray (5Y 5/2) color, while the lower side was black to very dark brown (1 OYR 2/1 to 2/2). Specimens were rounded to ovate on plan view, and had a domed cross-section, with their upper side slightly convex. Lichen diameter ranged from 1 or 2 cm to about 6 cm (Fig. 4), and height reached up to ~ 2.5 cm. Dry weight for individual thalli varied from 0.01 g to 3.89 g; average weight for all the lichens was 0.55 g. Therefore, total lichen biomass was around 45.6 g/m2. Lichen thalli were usually firm and withstood a fair amount of handling, but some of the larger specimens were breaking apart into two or more fragments; thus, as in other errant cryptogams (PEREZ 1991 a), there seems to be a maximum size limit imposed by the tensile strength of the vagant mass. Although ?all lichens were completely unattached to the substrate, several (19) had one or two small pebbles attached, usually on their underside (cf. MAGNUSSON 1944:

Fig. 4. Representative specimens of Xanthoparmelia vagans (NYLANDER) HALE, collected at 4530 m elevation. Scale is 15 cm long; each division is 1 cm. FLORA (1994) 189

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PI. 8). A few individual soil grains could be seen adhered to the lower sides of most lichens, but only one specimen had a small lump of fine soil attached to it. The majority of the vag ant lichens were pure monospecific globoids of X. vagans, but 5 contained small stems of the moss Grimmia longirostris HOOK, and 2 were closely intertwined with strands of Thamnolia vermicularis. At the time of collection, some lichens, particularly the smaller ones, were being gently swayed by a light wind of about 6 to 8 kmh, but no lichen transport away from the site was taking place. Dispersal of the loose thalli must take place with stronger winds, which normally occur during the rainy season. The highest wind velocity I ever measured in this area (in Aug. 1980, during a severe rain and snow storm) was of 48 kmh. This must have been unusual, as records for the nearby station of Mucuchies (3000 m) indicate that winds ~ 30 kmh are only attained during 2.4% of the time (ANDRESSEN & PONTE 1973). Usually, speeds during dry-season fieldwork over the past 13 years have remained moderate, around 13 to 15 kmh, with occasional gusts of up to 25.5 kmh. Nonetheless, wind speed is higher in exposed summits and peaks, and even during the dry season, sustained velocities of about 32 kmh may be common on the flanks of Pico Los Nevados and on the plateau where X. vagans was collected. The available data indicate that these lichens, particularly the smaller specimens, are probably transported by wind. Although wind velocity is higher during the rainy season, lichens are more prone to be saturated at that time, and therefore would be heavier. Thus, greater aeolian transport should perhaps be expected in the dry season. HEDBERG (1964: 69) found a vagant Xanthoparmelia species 'near X. vagans' both on Mts. Kenya and Kilimanjaro, and surmised that this lichen was transported by' solifluction'. I also consider frost an additional transport agent for the Andean paramo, as the lichens were found on nubbin-covered ground, but I believe that wind is mainly responsible for initially concentrating the loose thalli. The rough microtopography of the raised soil buds and nubbins should decrease wind velocity in a thin boundary layer near the ground surface, causing the lichens to drop from the air stream; the nubbins then 'trap' the lichens, of roughly their same size. As growing lichens increase in size and weight, or become interlocked in lumps, they are also less likely to be moved by wind, but thalli eventually break up in smaller fragments, which could then be dispersed to a new site. Sizable vagant populations ought to survive better in areas with sparse or no vegetation, as shading and litter deposition would interfere with lichen photosynthe268

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sis and development (cf. ROSENTRETTER & MCCUNE 1992).

3.3. Catapyrenium lachneum (ACH.) R. SANTESSON This squamulose lichen, previously known as Dermatocarpon hepaticum (ACH.) TH. FR. or D. lachneum (ACH.) A. L. SMITH, is commonly found growing closely attached to the soil in deserts and semiarid areas all over the world (FRIEDMANN & GALUN 1974, ROGERS 1977). It is also present in subpolar tundras of both hemispheres, including Greenland, Iceland, the Canadian archipelago, Alaska, the Yukon (THOMSON 1987), and the Subantarctic islands (DODGE 1973: 21). A few reports indicate its presence in mountain areas, such as those of New Zealand (MARTIN & CHILD 1972) and Mexico (THOMSON 1987). Catapyrenium lachneum had, until now, not been reported from South America (BREUSS 1993 a). In fact, the Venezuelan paramos represent the most equatorial occurrence of this species (BREUSS, 1993 b, pers. comm.). C.lachneum is a pyrenocarpous lichen; instead of apothecia, it has perithecia for fruiting bodies. These are immersed in the thallus and open at the surface through ostioles, visible as tiny black dots. C. lachneum is an important component in desert cryptogamic crusts (ROGERS & LANGE 1971, DANIN & BARBOUR 1982), where it acts as a soil consolidator by binding soil grains and preventing erosion (HALE & COLE 1988). Apparently, its squamulose structure, and the dense network of strands beneath the squamules, allow it to withstand a great deal of soil expansion and contraction, and other kinds of substrate disturbance, without becoming detached (LAWREY 1984: 288). There are no known erratic species or forms of Catapyrenium. IMSHAUG (1950) described a vagant species, Dermatocarpon vagans IMSH., in a closely related genus, but ROSENTRETTER & MCCUNE (1992) recently considered this 'species' as only an environmental modification of D. reticulatum MAGN., which produces vagant forms along with D. miniatum (L.) MANN in many steppe communities throughout western North America. A single population of erratic Catapyrenium lachneum was found at 4540 m, at the base of Pico Los Nevados and only 250 m from the collection site for X. vagans. These lichens, however, were not exactly detached from a substrate, since they consisted of spheroidal, pebble-like masses of soil covered by dark brown squamules on all sides (Fig. 5), which rested on the ground. Thus, these vagant specimens of C. lachneum resemble moss globoids more than any-

center',

Fig. 5. Lichen globoids of Catapyrenium lachneum (ACH.) R. SANTESSON, collected at 4540 m elevation. The white specks on the surface of some globoids are smal L quartz pebbles embedded in them. Each division of the scale is 1 cm. that,

thing else. To my knowledge, this is the first time such remarkable occurrence is reported for any lichens. WEBER (1967: 45) observed a similar adaptation in Aspicilia calcarea, which can form a continuous crust over all sides of small mobile pebbles. These are overturned by periodic solifluction and frost heaving, thus the lichens can eventually grow on all faces. ROSENTRETTER & MCCUNE (1992: 18) found the same phenomenon in several crustose lichens, mainly Aspicilia, in western Canada and USA. These authors also reported small balls of Cladonia pocillum 'with a bit of soil in the and ascribed these peculiar forms to repeated turning by frost heaving. The C. lachneum globoids were located on a SEfacing paramo slope of 6 to 8° inclination. As in the X. vagans site, the ground was covered by nubbins, but also by well-developed striated soil, which is produced by needle ice growth (PEREZ 1984). All specimens in the population (172) were gathered. This occupied an area about 12 by 9 m, without any vegetation other than a few isolated clusters of

Agrostis breviculmis growing at the edge of stone 'edafids' (HEDBERG 1964) and small patches of Arenaria musciformis. T. vermicular is and several moss globoids of G.longirostris were also present at the site. About 8 m upslope from the lichen globoids, a large discontinuous patch of unidentified epedaphic mosses with scattered Hypochoeris sessiliflora H.B.K., was in the process of rupture by needle-ice exfoliation [Rasenabschalung] (PEREZ 1992b). All globoids were detached from the ground. They were discontinuously but densely covered by many dark reddish brown to black (5YR 3/3 to 2.5/1) squamules, which contrasted sharply with the light brownish gray to grayish brown (10YR 6/2 to 5/2) color of the soil. Squamules ranged in size from 1 to 6 or 7 mm; they were generally present on all sides of the soil lumps. However, about 30% of the globoids, particularly larger and flatter ones, had greater lichen density on the 'upper' side, while these were lacking or scarcer on the opposite, 'lower' side. This is deemed to reflect a lower frequency of overturning in these globoid specimens. Soil lumps had irregular and often angular edges, were strongly flattened, and on plan view had a circular to mostly elliptical shape. Globoid diameter varied from,....., 2 cm to 6 or 7 cm. Weight ranged, accordingly, from 0.2 to 17.94 g; average dry weight was 4.17 g. All the globoids gathered from an area of about 100 m 2 weighed 718 g, but the bulk of this weight is contributed by the soil, not the lichens, which only formed a thin film over the soil balls. Globoids were extremely firm, and did not break when picked up. I collected soil samples from the site, to compare these with the soils found within the globoids; this will be reported in a coming pUblication. Detailed microscopic analysis revealed in addition to C. lachneum, other cryptogams had colonized the soil masses. Three of these contained several stems of the moss G. longirostris; one had a thalus fragment of X. vagans firmly embedded in soil. Two globoids had small areas covered by Marsupella spp. (Hepaticae); another contained a badly eroded bit of Riccia spp., also a hepatic (WEBER 1992, pers. comm.). Even though these lichen balls have not been previously observed elsewhere, their process of formation was clearly anticipated by WEBER (1962), who mentions how C. lachneum often occurs on "raised soil pedestals" surrounded by eroded depressions, and that needle ice can also completely overturn small blocks of soil, thus affecting soil lichens. In a later publication, WEBER (1977: 22) says: "On desert soil crusts, many lichens approach the vagant habit as the soil pedestals supporting them become smaller and more eroded basally under the influence of raindrop-splash erosion and eddying wind currents".

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Of these disturbance agents, needle ice is believed to cause the detachment and transport of the C. lachneum globoids in Piedras Blancas. Rain could also affect them, but it is very unlikely that wind could transport these heavy soil/lichen balls. Cattle actively disrupt and rupture the ground surface in this paramo (PEREZ 1993). It is also conceivable that cow trampling could produce the detachment of crusted pieces of soil, which are then rotated by frost action. In addition, animals may cause a localized density reduction of epedaphic C. lachneum, as observed elsewhere (ROGERS & LANGE 1971). Since cows normally restrict their feeding activities to valley floors and stream courses (PEREZ 1992c), whatever effects they induce must be intense in these areas, but nearly absent from the higher paramo reaches.

3.4 Grimmia longirostris

HOOK.

Grimmia is a cosmopolitan genus of acrocarpous mosses which form dense hummocky cushions. At least eight Grimmia species produce vagant moss balls in 10 locations worldwide (PEREZ 1991 a). In South America, two other areas are known to have moss globoids; both are high-altitude paramos. In Colombia, CLEEF (1981) found erratic specimens of Bryum argenteum, Racomitrium crispulum, and of an unidentified species of Grimmia. Recently, BLANCA LEON (1992, pers. comm.), found globoids of Grimmia (?) spp. at 4600 m on Guagua Pichincha, Ecuador. Other equatorial mountains with moss balls (all of Grimmia species) include Mts. Kilimanjaro, Kenya, and Elgon, in east Africa (HEDBERG 1964). I have already discussed in detail the morphology and ecology of moss balls in the Venezuelan paramo (PEREZ 1991 a), thus my comments here will be restricted to the most basic characteristics of moss globoids, and to some new data. In Piedras Blancas, vagant moss forms are produced by Grimmia longirostris HOOK., a species closely related to G. ovalis (HEDW.) LINDBL., which is a common erratic on east African highlands. G. longirostris is found throughout north and western South America, but is apparently not known from other Venezuelan localities (MAGILL 1990, pers. comm.). Since 1990, I have located several populations of G. longirostris globoids between 4290 and 4570 m, and have collected nearly 1000 specimens from nine of these populations. Small balls of G. longirostris are mere amorphous lumps of soil with a few moss shoots, but as they increase in size, become nearly spherical or ovoidal cushions densely covered by moss on all sides 270

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(Fig. 6). Moss-ball color changes depending on moisture content. If dry, they are very dark brown to black (10YR 2/2 to 2/1); when moist, they turn olive green to dark olive gray (5Y 3/3 to 3/2). Size ranges from a few mm to about 12 cm across. Ordinarily, moss-ball weight varies from just a few centigrams to about 35 g, although one exceptionally large globoid weighed 71.2 g. As moss balls get larger, needle ice or other transport agents - are not able to turn them as often, and moss shoots start dying on the side that rests against the ground. Vagant mosses then become flattened and are prone to being eroded; soon afterwards, they are fragmented and destroyed. Frequent globoid disturbance can result in arrested sexual reproduction, which is replaced by vegetative reproduction (RICHARDSON 1981), but a few moss balls with sporophytes were found in three populations (cf. HEDBERG 1964, BECK et al. 1986). A total of 24 reproducing balls (mostly large and heavy) were found; thus, they made up only about 2.5% of all globoids examined. As with other vagant cryptogams, G. longirostris is usually the only plant growing on moss globoids, but occasionally some species mixing takes place. In one population, 17% of the moss balls were commingled with T. vermicularis thalli, and 5% were invaded by a species of Stereocaulon 1• I also found three globoids with small embedded fragments of X. vagans, and two which contained several large squamules of C. lachneum. Although some authors indicate that moss globoids have pebbles in their center, those in Piedras Blancas normally have a sizable core of fine soil. Moss balls actually have four times as much silt and clay as the soils at their sites (PEREZ 1991 a). This is due to the exceptional ability of mosses to intercept and trap fine soil grains, both from aeolian sources and from the ground, between their shoots (cf. DANIN & YAALON 1981, DANIN & GANOR 1991). The fine soil inside moss globoids has greater water-retention capacity. Thus, it increases the chance of survival of the moss ball, enabling it as well to continue growing, in a fine example of biotic 'positive feedback'. Moss balls are found on a variety of sites, but the best developed globoids always occur on moist, gently sloping areas with frequent needle-ice formation and little or no vegetation. The agents for detachment and transport of moss balls are the same as those cited for Catapyrenium globoids. In this instance, I also consider needle-ice disturbance as the most effective means for moss-ball transport. Proof 1) Erratic specimens of Stereocaulon vesuvianum var. nodulosum have been found by CLEEF (1981) in the humid superparamos of Colombia.

Fig. 6. Moss globoids of Grimmia longirostris HOOK., collected at 4380 m elevation. One moss ball (second row, far left) has a small white piece of Thamnolia vermicularis still attached to it. Scale is 15 cm long; each division is 1 cm.

for this was obtained at two large bowl-shaped sites with periglacial stone pavements. These are zones of stone accumulation due to gradual migration by gravity and freeze-thaw action from the surrounding slopes (SCHUBERT 1975). Many large moss balls were found at the periphery of the depressions, on areas only partially covered by stones, where some soil was exposed at the ground surface. Here, I found numerous soil patches covered by ice needles 2 to 6 cm tall, which were topped at the time of my visit by large upheaved moss balls. Globoids seemed to have migrated downslope towards the 'bowl' center, but were sharply concentrated on a 12 to 15 meterwide band around the depression bottom, and had collected just at the point where this was totally covered by stones and lacked any exposed soil. Despite the fact that soil beneath the stones at the bowl center was thoroughly saturated (owing to its topographic position), no needle ice formed there due to the continuous cover of rocks. Since the main difference between the peripheric area occupied by moss balls and the globoid-free bowl center was the lack of soil and needle ice in the latter, I must conclude that moss balls in Piedras Blancas are transported by needle ice, and probably by little else other than gravity. Moss balls are part of a continuum of forms, which can be clearly observed in most paramo sites. First, cushions are tightly attached to boulders or outcrops. Some mosses are found partially detached but still clinging to the rock surfaces. Recently detached

hemispheric cushions or fragments, with moss shoots growing only on one side of the mass, may be seen at the base of the rocks. Finally, fully developed, mobile globoids extend some distance downslope from outcrops. I have found evidence for several additional agents of moss detachment from boulders. On one visit, the paramo was very dry, and numerous desiccated moss cushions had cracked and become partially detached from outcrops. Drought probably suffices to separate cushions from the rocks, but this process can be greatly accelerated by 'debris wedging'. As surface soil creeps downslope due to needle-ice disturbance, fine grains and pebbles first accumulate upslope from, and then cascade over, blocks and outcrops. Partially detached moss cushions on the downslope vertical faces of these rocks may capture some of this debris 'rain' along the opening crevice between the moss and the rock, which is wedged apart by the weight and pressure of the accumulating debris!. At one site, I found a large population of moss balls sharply concentrated below rocks. The ground next to the rocks was riddled with fresh den holes, excavated by paramo rabbits (Sylvilagus brasiliensis) ; many rabbit droppings were also found between the moss balls. I imagine that rabbits would find mosses palatable, and that in the process of nibbling 1) These tiny fissures curiously resemble 'Bergschrund' crevasses, found between glaciers and their bedrock headwall, which also collect falling, but much larger, debris.

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them would be responsible for detaching a fair amount of moss fragments from the rocks, thus initiating the process of globoid formation.

3.5. Marsupella spp. The last type of vagant cryptogam involves an undetermined species of Marsupella DUMORT. (Hepaticae). The genus M arsupella, in the family Gymnomitriaceae, contains about 42 species and is largely confined to the northern hemisphere, with localized extensions into tropical mountains. Most Marsupella species are found in arctic and alpine areas, where they are pioneers in the most 'inhospitable' environments; at high elevations, they can be usually found forming compact turfy mats on bare mineral soils of fully insolated sites with an extreme degree of exposure. Several species are often found 'on patches where the poor soil has been turned bare, e.g., by frost heaving' (SCHUSTER 1974: 33). In South America, Marsupella has been reported from the high Colombian Andes (WINKLER 1976) and from alpine areas of Tierra del Fuego, Argentina (SCHUSTER 1974). In Piedras Blancas, Marsupella is the most important component of thin (4 - 8 mm) superficial cryptogamic crusts found extensively throughout this paramo above approximately 4000 m. Although these microphytic crusts are very common in warm deserts, they have apparently never been reported for tropical alpine areas. Marsupella also produces a dense dark cover on soil buds at the highest paramo elevations. As is common in this genus (SCHUSTER 1974: 17), Marsupella-covered buds are usually restricted to coarse sandy soils developed on igneous (granite) or metamorphic (granitic gneiss, quartzite) rocks. Paramo soil buds are sometimes also covered by G. longirostris, which is present in the crusts as well. Comparable organic crusts on nubbins and buds were found by WASHBURN (1973: 82) in Greenland, and by LLANO (1962: 212) in McMurdo Sound, Antarctica!. WINKLER (1976: 802) also mentioned small cushions [,Polsterbildungen'l of Marsupella trolliiin the dry paramos of the nearby Sierra Nevada de Santa Marta, which suggest soil buds similar to those in Venezuela. Marsupella buds are small, hemispheric, lumpy mounds of soil, 3 to 12 cm across, and up to 5 or 6 cm high (Fig. 7). Their surface is black (7.5 YR N2/1) to very dark gray (10YR 3/1), in marked contrast with the light brownish gray (10YR 6/2) of the surrounding bare soil. The ground between buds is often covered by small 1) Soil buds or clumps in Antarctica are, however, covered by blue-green algae. 272

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Fig. 7. Small soil buds covered by a dark cryptogamic crust of Marsupella spp. Paramo de Piedras Blancas, 4545 m elevation. Note how the light, low-lying areas between soil buds are devoid of any cryptogamic crust and have an abundance of white quartz pebbles. The photo shows an area ~ 60 cm wide in the middle ground ; the lens cap on the lower left has a diameter of 57 mm. Jan. 1988.

pebbles, which are sorted out of the buds and concentrated on the intervening areas by frost activity (PEREZ 1992 a). Only nine vag ant specimens with Marsupella were found at 4540 m, mixed with the globoids of C. lachneum. The erratic M arsupella were small lumps of soil and peaty material, and closely resembled those of C. lachneum; their weight varied from 0.24 to 4.07 g (mean: 1.62 g). Only small parts of the globoid surface were occupied by minute Marsupella stems and leaves, which looked badly eroded and/or dead. Close examination revealed that two vagant Marsupella globoids were also occupied by C. lachneum, and two more contained shoots of G. longirostris. I believe that these erratic specimens were produced by detachment of nearby crusted buds, which are

abundant over a large area only 300 m upwind from the collection site. Disturbance of Marsupella buds may have been caused by frost, desiccation, wind, or cattle trampling. Because these vagant forms did not look very healthy, and I have never found other populations despite the common occurrence of M arsupella crusts and buds in the paramo, erratic M arsupella may not be very common and/or survive for long in an unattached condition. More conscientious search might, nonetheless, lead to the discovery of similar populations in future visits to the area.

4. Conclusions The vagant cryptogams of the high Venezuelan paramo form a unique type of community, not previously described for the Andean cordillera. Because all these species occur together - and even commingled - in many high-paramo sites, they are considered to constitute a true plant association. Similarly diverse communities of erratic cryptogams, mainly lichens, have been found elsewhere; they include those of the Chilean fog oases (FOLLMANN 1966,1967), and of the Russian steppes (MEREWSCHKOWSKY 1918), which KLEMENT (1955: 107) called the 'Parmelietum vagantis,l. Some relevant ecological questions can be asked. Why are vagant forms restricted to the high paramo? Apparently, the environmental requirements for their development and survival are met there, but not at lower elevations, where erratic plants are absent. These conditions seem to include: (1) bare, silty soils on level ridge summits, shallow basins or gentle slopes which attain high moisture levels, (2) recurrent frost activity and needle-ice growth, (3) exposed locations periodically subjected to persistent and/or strong winds, (4) lack of vascular vegetation and plant litter which would shade or cover the substrate over which the vagant plants rest, and, (5) for facultative vagant species, local availability of adnate 'mother' plants growing on rocks and soils, which will act as sources of vegetative propagules. What specific 'purpose' does a vagant life form serve? Several important possible consequences of the erratic habit can be surmised within various botanical areas: (1) Competi tion. A vag ant life form may confer some competitive advantage to the cryptogam species that can develop it, as they are able to occupy locations where other species that lack this adaptive 1) Actually, there is no Xanthoparmelia vagans in this association, mainly characterized by X. camtschadalis and X. suhdiffluens (see HALE 1990).

behavior are excluded (SHACKLETTE 1966). This provides a rationale as to why loose cryptogamic forms are abundant wherever local conditions are too harsh for vascular plants. (2) Environmental adaptation. The erratic habit allows the colonization of, and continuous survival on, substrates that are too unstable to support attached cryptogamic forms (cf. ROGERS 1977). In this view, loose forms are mainly an adaptation to severe environmental conditions, such as constant soil heaving by frost, or repeated animal trampling. Thus, a habitat that would otherwise remain unoccupied is utilized (i.e., an 'empty niche' is filled) by these cryptogamic 'modifications' (WEBER 1977). (3) Life-span and mortality rates. The ability to remain alive after becoming detached from the substrate would clearly postpone the death of individual plants, thus reducing overall mortality rates in the population. Chances of population survival increase as detached specimens which would otherwise have died continue living even under adverse conditions. (4)Asexual reproduction and site coloniz a t ion. For facultative erratic species, the vagant habit is an efficient method of dispersal via asexual reproduction, important for the establishment of new colonies in sites where sexual reproduction may be limited or only marginally possible (cf. SHACKLETTE 1966, KANDA 1987). Such species, like Catapyrenium lachneum and Grimmia longirostris, could presumably re-attach themselves to a new (stable) substrate after transport. (5) E v 0 I uti 0 nan d dis per sal. Du RIETZ (1931) discussed on detail the role of wind in the dispersal and ecology of alpine lichens. MEREWSCHKOWSKY (1918: 30) already indicated that obligate vagant lichens had evolved to survive in harsh environments, where spores might have little chance of finding the algae needed for the formation of a new thallus. Indeed, a most striking result of the unattached life style is lichen sterility, as fungi loose their ability to produce apothecia (WEBER 1977, HALE 1990). Since erratic lichens reproduce only by thallus fragmentation, they become totally dependent on wind, frost, or other external agents for dispersal. The worldwide concentration of erratic lichen species in windy areas prompted WEBER (1977: 23) to consider wind as a primary agent of natural selection in the evolution of vagant taxa. Given that erratic lichens and other cryptogams are also common in regions with high frost frequency, a similar evolutionary role should be ascribed to this last environmental factor. FLORA (1994) 189

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5. Acknowledgements I am grateful to Drs. BRUCE ALLEN and ROBERT E. MAGILL (Missouri Botanical Garden), OTHMAR BREUSS (Naturhistorisches Museum, Vienna), DANA GRIFFIN, III (Univ. of Florida), BILLIE L. TURNER (Univ. of Texas), and WILLIAM A. WEBER (Univ. of Colorado), for their kind help with plant identification. Financial support was provided by the Research Institute (Univ. of Texas, Austin), and by the Institute of Latin American Studies at the U niv. of Texas from funds provided by the Andrew W. Mellon Foundation. I thank O. VERA, H. HOENICKA B., and A. LUCCHETTI, for their valuable assistance with field work. My father, FRANCISCO PEREZ CONCA, helped with travel logistics. Drs. A VINOAM DANIN (Hebrew Univ. of Jerusalem, Israel), STEPHAN HALLOY (lnvermay Agricultural Centre, New Zealand), and WILLIAM A. WEBER (Univ. of Colorado) kindly brought to my attention several interesting publications. This manuscript greatly benefited from a critical review by Drs. INES L. BERGQUIST, A VINOAM DANIN, JOSEF POELT, and from several discussions with my students.

Resumen Se describen cinco tipos de criptogamas vagantes para las areas mas altas del Paramo de Piedras Blancas, en los Andes de Venezuela. El viento transporta especimenes libres, completamente sueltos, de los liquenes Thamnolia vermicularis (Sw.) ACH. ex SCHAERER y Xanthoparmelia vagans (NYLANDER) HALE. T. vermicularis es la planta vag ante mas comun en este paramo, donde es practicamente ubicua. Las poblaciones de X. vagans son mas restringidas, y se han encontrado solo por arriba de los 4375 m. Pequefios terrones esferoideos de suelo, cubiertos por el liquen Catapyrenium lachneum (AcH.) R. SANTESSON 0 por el musgo Grimmia longirostris HOOK. son perturbados y transportados por la actividad congelatoria del suelo (hielo acicular) y por descenso gravitatorio. Solo se hallo una densa poblacion de globoides de C. lachneum a 4540 m, mientras que varias poblaciones de bolas de musgo de G. longirostris se encontraron entre 4290 y 4570 m. La superficie del suelo en el alto paramo presenta comunmente pequefios monticulos de tierra y nubbins que estan frecuentemente cubiertos por una especie no identificada de la hepatica M arsupella. Unos pocos ejemplares globulares de esta hepatica con inclusiones de suelo se hallaron a 4540 m; estos fueron probablemente desprendidos del suelo por 274

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hielo acicular. Esta diversa comunidad de criptogamas vagantes es la primera que se ha descrito jamas para la cordillera de los Andes.

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