Lichens in Puerto Rico: An 

Ecosystem Approach

Joel A. Mercado-Díaz, William A. Gould, Grizelle González, and Robert Lücking 

United States Department of Agriculture

Forest 

Service

International Institute 

of Tropical Forestry

General Technical Report

IITF-GTR-46

April

2015
Authors

Joel A. Mercado-Díaz is an associate researcher, William A. Gould is a research 

ecologist, and Grizelle González is a project leader, U.S. Department of Agriculture, Forest Service, International Institute of Tropical Forestry, Jardín Botanico 

Sur, 1201 Calle Ceiba, San Juan, PR 00926-1119; Robert Lücking is a collections 

manager (fungi) and adjunct curator (lichens), Science & Education, The Field 

Museum, 1400 South Lake Shore Drive, Chicago, IL 60605-2496. 

Cover: Herpothallon rubrocinctum growing on a bamboo shoot (Bambusa vulgaris) 

in the Central Mountain Range, Puerto Rico. Photo by J.A. Mercado-Díaz.

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Service office. USDA is an equal opportunity provider and employer. 
Lichens in Puerto Rico: An Ecosystem Approach

Joel A. Mercado-Díaz, William A. Gould, Grizelle González, and Robert Lücking 

U.S. Department of Agriculture

Forest Service

International Institute of Tropical Forestry

San Juan, Puerto Rico

General Technical Report IITF-GTR-46

April 2015 
ii

Abstract

Mercado-Díaz, Joel A.; Gould, William A.; González, Grizelle; Lücking, 

Robert. 2015. Lichens in Puerto Rico: an ecosystem approach. Gen. Tech. Rep. 

IITF-GTR-46. San Juan, PR: U.S. Department of Agriculture, Forest Service, 

International Institute of Tropical Forestry. 76 p.

This work presents basic information on tropical lichenology. It also describes 

general aspects about the ecology and biodiversity of these organisms in eight 

forest ecosystems present along an elevational gradient in northeastern Puerto Rico. 

These ecosystems consist of elfin woodlands, palo colorado, sierra palm, tabonuco, 

lowland moist, dry, mangrove, and Pterocarpus forests. Lichen communities are 

mainly described in terms of general ecological attributes (e.g., species richness, 

common species, etc.). Basic information about the environment and vegetation 

found in these forests is also provided. The information presented is supplemented 

with field and microscopic photographs of species and their habitats.

Keywords: Tropical lichens, Puerto Rico, forests, conservation.
iii

Contents

1 Introduction

1 What Are Lichens?

7 Lichenology in Puerto Rico

8 Lichens in Puerto Rican Ecosystems

11 Methods

11 Study Areas

13 Sampling Scheme

14 Forest Health and Thelotremoid Lichens

17 Organization and Other Considerations

18 Forests

18 Elfin Woodland Forest

22 Palo Colorado Forest

26 Sierra Palm Forest

29 Tabonuco Forest

33 Lowland Moist Forest

36 Dry Forest

62 Mangrove Forest

65 Pterocarpus Forest

68 Concluding Remarks

69 Acknowledgments

69 English Equivalents

70 Literature Cited

75 Glossary
iv

Preface

This report aims to introduce the reader to general concepts in lichenology with a 

particular emphasis in tropical lichens and the study of lichens in Puerto Rico. It 

also intends to describe in a broad manner the main characteristics of lichen communities present in different forest ecosystems of the island, and the environmental 

conditions in which they thrive. Although care was taken in following basic rules 

for responsible scientific investigation and writing, the information presented here 

is aimed to appeal to a more general audience. Moreover, this work presents ideas 

that may stimulate the formation of new research questions concerning the lichen 

flora of Puerto Rico, and consequently increase interest in and appreciation for the 

study of this amazing group of symbiotic organisms.
1

Lichens in Puerto Rico: An Ecosystem Approach

Introduction

What Are Lichens?

For centuries, lichens have been an intriguing group of organisms for scientists 

mostly because of the difficulties that botanists and taxonomists have faced in their 

classification (fig. 1). Today, the symbiotic nature of lichens is well understood. In 

1982, the International Association of Lichenology described lichens as “an association between a fungus and a “photosynthetic partner,” which results in a stable 

thallus with a specific structure.” Most of the fungi that become lichenized belong 

to the division Ascomycota. Only 1 percent of lichens have a fungal component 

from the division Basidiomycota. The fungal partner in a lichenological association 

is better known as the mycobiont, which is also the source for the species name in 

lichens. The photosynthetic partner, or photobiont, is usually an alga within the 

classes Trebouxiophyceae and Ulvophyceae (Leliaert et al. 2012). Cyanobacteria, 

formerly called “bluegreen algae,” also participate in lichenization. In some lichens, 

such as species in the genus Stereocaulon, both algae and cyanobacteria may be 

found within the same thallus. 

Prompted by the symbiotic nature of lichens, scientists have been interested 

in studying how the mycobiont and the photobiont behave outside the lichen association. In fact, individual components of lichen species have been successfully 

separated in vitro; not surprisingly, their appearance is usually in sharp contrast 

to the lichenized form (fig. 2). The mycobiont is usually amorphous and has slow 

growth rates; therefore, it is believed that, for most of the mycobionts, lichenization 

is obligate (Nash 2008). 

Depending on the species, the photobiont may grow successfully in a freeliving state. For example, tropical filamentous algae Trentepohlia is commonly 

found free-living (fig. 3), but for the green algae Trebouxia, survival outside 

lichenization is rare.

Lichens come in a variety of colors and growth forms and are able to colonize 

almost every type of substrate that an environment could provide. Although the 

most common colors in lichens are grey, pale green, and yellowish-green, some 

species are capable of producing secondary compounds that make them orange, 

red, or yellow (Brodo et al. 2001). There are six main types of growth forms in 

lichens: crustose, foliose, squamulose, fruticose, dimorphic, and pendulous (fig. 

4). The size of these growth forms is highly variable, from less than a few millimeters in some crustose species to more than 2 m in some pendulous Usnea species. 

Although the majority of species fit into one of these types, it is not uncommon 

to find intermediate forms. 

Lichens are a symbiotic 

association between 

a fungus and a photosynthethic partner.

1

 Note: terms in boldfaced type are defined in the glossary (page 75).
2

GENERAL TECHNICAL REPORT IITF-GTR-46

Figure 1—Lichens growing on a tree stump in Aibonito, Puerto Rico. 

J.A. Mercado-Díaz
3

Lichens in Puerto Rico: An Ecosystem Approach

Figure 2— (A) Acarospora fuscata in lichenized 

state; (B) (flask on left) the photobiont of A. fuscata; 

(flask on right) the mycobiont of A. fuscata.

Figure 3—Colonies of Trentepohlia algae colonizing the branches of a tree in an elfin woodland forest, El Yunque National Forest, 

Puerto Rico.

A B

Stephen Sharnoff

Vernon Ahmadjian J.A. Mercado-Díaz
4

GENERAL TECHNICAL REPORT IITF-GTR-46

Figure 4—Common growth forms found in lichens. (A) Crustose [Graphis spp.], El Yunque National Forest, Puerto Rico; (B) 

Foliose [Sticta spp.], El Yunque National Forest, Puerto Rico; (C) Squamulose [Acarospora socialis], Sierra Bermeja, Puerto Rico; 

(D) Fruticose [Cladina sandstede], Maricao, Puerto Rico; (E) Dimorphic [Cladonia subradiata], El Yunque National Forest, Puerto 

Rico; (F) Pendulous [Usnea spp.] Maricao, Puerto Rico. Photos by: J.A. Mercado-Díaz, R. Lücking, and A. Cuevas-Padró.

B

C D

E F

A

J.A. Mercado-Díaz J.A. Mercado-Díaz

R. Lücking

R. Lücking

A. Cuevas-Padró A. Cuevas-Padró
5

Lichens in Puerto Rico: An Ecosystem Approach

Rocks and the bark of trees are usually the preferred colonization substrates for 

lichens; however, they have been found growing on all types of natural and artificial substrates including leaves, wood, concrete, glass, plastic, and metal (fig. 5) or 

even the carapace of some insects (Lücking et al. 2010). Lichens produce a number 

of morphological and anatomical characteristics that their component organisms 

would not develop in their free-living forms (Ahmadjian 1993, Brodo et al. 2001, 

Nash 2008). Examples of these features include cilia, rhizines, and cyphellae. 

These attributes are also used for taxonomic identification. 

Figure 5—Several foliose and crustose lichens growing on human-made structures, Jardín Botánico Norte, Río Piedras, Puerto Rico.

In terms of nutrition, the photobiont provides most of the organic nutrients to 

the mycobiont. For green algal lichens, carbohydrates are transferred to the mycobiont in the form of sugar alcohols, and for cyanobacterial lichens in the form of 

glucose (Nash 2008, Purvis 2000). Benefits gained for the photobiont from lichenization are not so apparently obvious, especially because it has been observed that, 

in a lichenized state, some photobionts grow more slowly than in their free-living 

form (Nash 2008). In spite of this, studies have found that the mycobiont facilitates 

the absorption of mineral nutrients, enhances water uptake to the photobiont, and 

protects it from light damage in sun-exposed environments, which suggests that 

the photobiont does actually gain some benefits from lichenization. 

J.A. Mercado-Díaz
6

GENERAL TECHNICAL REPORT IITF-GTR-46

It remains undisputed that in the lichenized state, both the mycobiont and the 

photobiont are capable of thriving in environments in which they would not survive 

individually. This would probably explain why lichens colonize almost every 

ecosystem in the world, from tropical rain forests to polar environments (Brodo et 

al. 2001, Purvis 2000). In this respect, lichens were initially believed to be more 

diverse in temperate ecosystems, a notion supported by several misleading lichen 

surveys (Lücking et al. 2011). However, at smaller scales, (e.g., looking at uniform 

area sizes of 100 km2, 10 km2, 1 km2, or even 1 ha), lichen species richness clearly 

increases toward lower latitudes (Lücking et al. 2011). Estimates of world species 

richness of lichens range from 13,500 (Hawksworth and Hill 1984) to 18,000 

species (Sipman and Aptroot 2001). Yet, a more recent study has suggested that 

the extent of world species richness may be about 28,000, with at least half of the 

species (14,000) occurring in the tropics (Lücking et al. 2009a). Compared to their 

fungal counterpart, photobiont diversity is less conspicuous, with nearly 54 genera 

and about 100 species of algae and cyanobacteria reported (Ahmadjian 1967, Büdel 

1992, Frey 2012, Tschermak-Woess 1988). For years lichenologists believed that 

lichen photobionts had little influence on thallus morphology. Nevertheless, recent 

discoveries, like the continually increasing description of new species forming 

photosymbiodemes (Moncada et al. 2013), shows that at least for some groups, 

photobionts have a stronger influence on thallus morphology than was previously 

supposed. 

The symbiotic association of lichens is still a controversial topic among 

lichenologists and taxonomists, mostly because the nature of this association does 

not fit precisely in any of the known examples of ecological symbiosis. Perhaps 

the most appropriate categorization of the lichen symbiosis would be “controlled 

parasitism,” because the mycobiont negatively affects the physiognomy and metabolism of the photobiont without killing it (Ahmadjian 1993, Schwendener 1869). 

Goward (1994) referred to this relationship as “fungi that have discovered agriculture.” Evidence from a recently described lineage of cyanobacteria (Rhizonema) 

strongly supports this view of the lichen symbiosis (Lücking et al. 2009b). However, 

recent discoveries have shown that lichens are made of much more than fungal 

and photobiont components. A number of endolichenic bacteria and fungi with 

distinctive chemical properties have been found in different lichen thalli (Arnold 

2007, Cardinale et al. 2006); hence lichens may be more appropriately regarded as 

miniature ecosystems (Nash 2008).

Because of the diversity 

of microorganisms 

that have been found 

to inhabit the lichen 

thallus, lichens 

are often regarded 

as “miniature 

ecosystems.”
7

Lichens in Puerto Rico: An Ecosystem Approach

Lichenology in Puerto Rico 

The field of lichenology in Puerto Rico began in 1820 

with the identification of two species from Puerto 

Rico in a report by Sprengel (1820), and a subsequent 

report titled “Lichenes Portoricenses,” published by 

Jean Müller Argoviensis in 1888 (fig. 6). However, not 

until the beginning of the 20th century were significant 

contributions to Puerto Rican lichenology made by 

scientists from the United States and Europe. Some 

of these included world-renowned lichenologists of 

that era, such as Bruce Fink, Edvard A. Vainio, and 

Alexander Zahlbruckner (Mercado-Díaz and SantiagoValentín 2010). Lichenology on the island was nearly 

abandoned until 1972 when a monograph of the lichen 

genus Ramalina in Puerto Rico and the Caribbean 

was presented by Landrón-Concepción (1972), then in 

the late 1980s with the publication of Working Keys of 

Lichenized Fungi from Puerto Rico (Harris 1989). 

Recent efforts promoting lichenology in Puerto 

Rico include the research project under which this 

report is supported: “Characterizing lichen communities along an elevational gradient in Puerto 

Rico: assessing their role as indicators of forest 

health, biodiversity and microclimate,” led by Joel A. 

Mercado-Díaz and William Gould. Also, a workshop 

titled “Taller de Liquenología Tropical: los micro y 

macro-líquenes de Puerto Rico,” held in 2011 at the 

University of Puerto Rico and organized by Joel A. Mercado-Díaz and Robert 

Lücking, resulted in the identification of at least 5 new lichen species and documentation of 25 species previously unknown to Puerto Rico, as well as the training of 

14 participants in tropical lichenology (Mercado-Díaz 2011). 

Finally, Lichens of Puerto Rico, a website at http://lichensofpuertorico.herbario.

upr.edu/, presents a list of the currently known lichens and lichenicolous fungi 

species that occur in Puerto Rico (Mercado-Díaz 2009). For more information 

about the history of lichenology in Puerto Rico, refer to Mercado-Díaz and 

Santiago-Valentín (2010). 

Figure 6—Cover of the report Lichenes Portorricenses, 

published by Jean Müller Argoviensis in 1888.
8

GENERAL TECHNICAL REPORT IITF-GTR-46

Lichens in Puerto Rican Ecosystems

Only occasionally do lichens comprise most of the biomass in forests; however, 

they play many ecological roles in these ecosystems (Will-Wolf et al. 2002). Lichens 

occupy nearly 8 percent of the Earth’s terrestrial surface (Ahmadjian 1993), and it 

is highly likely that their most prominent role in terrestrial ecosystems is related to 

their ability to facilitate primary succession. In this respect, lichens are among the 

first organisms to colonize newly exposed surfaces, such as rocks formed after the 

cooling of recently erupted lava or soil exposed by a landslide. Lichen growth and 

expansion result in mechanical and chemical abrasion that speeds up the natural 

weathering process of these surfaces and therefore accelerates soil formation. 

Colonization over smooth, inhospitable rock surfaces is therefore the most important contribution lichens make to soil formation and consequently to primary 

colonization (Brodo et al. 2001). 

Lichens are also important agents of soil stabilization and may represent a 

source of nitrogen and organic matter in some soils (Brodo et al. 2001, Jones 1988). 

Lichen colonization in disturbed and sandy soils may also be important for controlling erosion and the sedimentation of water bodies. As early colonizers, lichens are 

critical components of landslide recovery (Walker and Shiels 2013). In Puerto Rico, 

the growth of Stereocaulon ramulosum in recently exposed soil resulting from 

landslides or the construction and expansion of roads in mountainous areas of the 

island may constitute an important biological buffer against this type of disturbance 

(fig. 7a). Vast patches of different Cladonia species, like C. subradiata and the 

endemic C. robusta, have been observed growing in the siliceous sands of Laguna 

Tortuguero in Vega Baja and may contribute to reducing losses of sand via wind or 

water movement (fig. 7b).

As in other tropical regions, most of the lichen species in forests in Puerto 

Rico are epiphytic, classified either as foliicolous or corticolous. In areas of high 

Figure 7—(A) Stereocaulon ramulosum growing in recently exposed soil along a road in El Yunque National Forest, 

Puerto Rico; (B) Growth habit of Cladonia subradiata.

J.A. Mercado-Díaz

R. Seavey and J. Seavey

By colonizing and 

accelerating the 

erosion of newly 

exposed surfaces, 

lichens facilitate the 

formation of soils.
9

Lichens in Puerto Rico: An Ecosystem Approach

humidity with adequate light exposure (e.g., elfin woodlands in El Yunque National 

Forest), mosses and liverworts grow faster than lichens and therefore colonize most 

of the available epiphytic substrate area in these ecosystems. On the contrary, in 

forests with lower humidity like the Northern Karst Belt and the Guánica State 

Forest, lichens are possibly among the dominant epiphytes, at least in terms of the 

number of species. 

Lichens are believed to have an important role in water and nutrient cycles in 

forest ecosystems (Beckett 1995, Green and Lange 1991, Zotz et al. 1998). For many 

species, the lichen thallus is capable of storing up to 800 percent of its dry weight 

in water. This water, which is initially absorbed by direct assimilation from water 

vapor or rainwater, is released slowly to the environment, thereby influencing the 

immediate microclimate. Tree-dwelling lichens absorb a significant amount of 

nutrients from rainwater that passes through the canopy over the leaves, and differentially absorb minerals as water flows down to the soil (Brodo et al. 2001, Knops 

et al. 1991). Fruticose lichens like Ramalina menziesii have been shown to significantly affect the interception of rainwater and the deposition of water and nutrients 

in throughfall collected beneath the canopy in some temperate ecosystems (Knops 

et al. 1996). These effects potentially influence the composition and concentration 

of nutrients in underlying soils. Although it is likely for this kind of influence on 

water and nutrient status in trees and soils to be considerable in some forest areas of 

Puerto Rico (especially those where fruticose and foliose lichens are frequent), little 

is known about this subject in tropical ecosystems, thus it represents a promising 

research topic that deserves further investigation. 

It is possible that some of the nitrogen fixed by cyanobacterial lichens leaches 

from the lichen thallus or becomes available to neighboring plants when the lichen 

dies (Brodo et al. 2001), hence contributing to soil fertilization and consequently 

vegetation growth. Although quantitative estimates for this type of fertilization are 

scarce, it is not unreasonable to suggest that areas with the highest diversity and 

abundance of cyanobacterial lichens are the places where this mode of fertilization 

is more likely. One of the places in Puerto Rico where this may happen is in El 

Yunque National Forest, which has a relatively high diversity of species with cyanobacterial photobionts such as Stereocaulon, Peltigera, Dictyonema, and Sticta.

Some evidence appears to indicate that lichens are being used as a food source 

by several animals and insects in Puerto Rico. For instance, the tracks of what 

appears to be a snail possibly feeding on the thalli of several crustose species have 

been observed on numerous leaf, bark, and other artificial surfaces in El Yunque 

National Forest and other forests of the island1

 (fig. 8). Some of these tracks may 

1

 Mercado-Díaz, J.A. 2014. Personal observation.
10

GENERAL TECHNICAL REPORT IITF-GTR-46

belong to Scharammia alta, an endemic snail known from Luquillo and other 

places around the island that presumably feeds on encrusting algae and lichens.2

Gastropod grazing and lichen growth have been negatively associated for years; 

however, recent studies suggest that gastropods grazing on lichens may represent 

important vectors for lichen dispersal (Bosh et al. 2011). On the other hand, the 

frequent observation of pyrenocarpous lichens lacking their fruiting bodies 

(perithecia) may represent important evidence of direct grazing by insects. 

Lichens appear to be important nesting material for some bird species on 

the island. For example, fragments of foliose species like Parmotrema and Hypotrachyna are found in almost every hummingbird nest (fig. 9). These pieces of 

lichen are most likely part of a camouflage strategy by birds to evade predation of 

nestlings. Insects may also be using lichens for camouflage; there is documentation 

that the carapace of some tree-dwelling insects in Puerto Rico and Hispaniola 

resembles the patterns of lichens growing on leaves or tree trunks.3 4

Figure 8—Lichen thallus with grazing “tracks” (reddish areas), which are evidence of the feeding 

activities of a snail. This lichen is growing on an artificial substrate (a car door).

2

 Robinson, D.G.; García-Díaz, W.; Fields, A.; Pérez, J., Tang, T. 2011. The terrestrial malacofauna of Puerto Rico and the U.S. Virgin Islands. Unpublished manuscript. Washington, 

DC: U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Plant 

Protection and Quarantine. 107 p.

3

 Mercado-Díaz, J.A. 2014. Personal observation.

4

 Torres-Santana, C. 2014. Personal observation. Director, Arboretum Parque Doña Inés, 

Fundación Luis Muñoz Marín, RR 2 Buzón #5, San Juan, PR 00926-9766.

J.A. Mercado-Díaz
11

Lichens in Puerto Rico: An Ecosystem Approach

Figure 9—A hummingbird resting in a nest completely covered with foliose lichens.

There are at least 1,181 recognized species of lichenized fungi in Puerto Rico 

(Mercado-Díaz 2009); however, a recently published work proposes that the island 

may harbor around 1,600 species (Lücking et al. 2009a). Based on the checklist of 

lichens and lichenicolous fungi of Puerto Rico (Mercado-Díaz 2009) and preliminary results from a tropical lichenology workshop in the island (Mercado-Díaz 

2011), the real diversity of the island may reach about 2,000 species. This is almost 

half of the species known for the whole continent of North America.5

Methods

Study Areas

Most of the information presented in this report comes from intensive lichen 

collecting activities conducted by Joel A. Mercado-Díaz between August 2011 

and October 2012. Lichens were collected around the periphery of 10 × 10 m2

plots that were established for a study characterizing several biological and environmental parameters along an elevational gradient (fig. 10; González and Luce 

2013; González et al. 2013, 2007; Gould et al. 2006; Medina et al. 2013; Ping et al. 

2013). Lichens were sampled in 24 sites concentrated in northeastern Puerto Rico 

(fig. 11). These plots are representative of eight forest types: elfin woodland, sierra 

palm forest, palo colorado forest, tabonuco forest, lowland moist forest, dry forest, 

mangrove forest and Pterocarpus forest (Gould et al. 2006). Surveys were made in 

three replicate areas for each forest type (24 sites). 

5

 Lücking, R. 2013. Personal observation. 

José González Díaz

There may be around 

2,000 species of 

lichens in Puerto Rico, 

which represents 

nearly half of the 

species known for 

the continent of North 

America.
12

GENERAL TECHNICAL REPORT IITF-GTR-46

Figure 11—Location of the 24 sampling sites in northeastern Puerto Rico where lichen collecting activities for this study were 

completed. 

Figure 10—Sequence of eight forest types along a gradient of elevation, rainfall, and distance from 

the coast in northeastern Puerto Rico.
13

Lichens in Puerto Rico: An Ecosystem Approach

Sampling Scheme

Corticolous lichens were collected in sampling sites following a nonquantitative 

opportunistic sampling method (Cáceres et al. 2008). Because plots used for the present study are intentionally located far from widely used trails in areas of homogeneous forest cover representative of particular ecosystems (Gould et al. 2006), lichen 

collection followed a slightly different approach than was used by Sipman (1996) and 

Cáceres et al. (2008), in which lichen collecting efforts were concentrated on main 

trails and occasionally at points within the forest. In this respect, information about 

lichen communities presented here corresponds to forest ecosystems with continuous 

canopy cover, which represent the vast majority of the forested land area of Puerto 

Rico (Brandeis and Turner 2013). Nonetheless, to partly compensate for the apparent 

underrepresentation of the lichens present in open areas in these forests, lichens were 

also collected around canopy openings commonly encountered during collecting 

activities. This additional information was used to supplement the descriptions of 

lichen communities presented in subsequent sections. 

Lichen surveys were similar in practice to the nonquantitative opportunistic 

sampling strategy used by Cáceres et al. (2008). Trees were approached both randomly and subjectively depending on visual identification of conspicuous lichen 

thalli. Each tree was inspected for 3 to 5 minutes and specimens were collected for 

each lichen thallus recognized as a different species in each tree. From 20 to 60 trees 

were inspected at each site and between 50 to 100 lichen samples were collected per 

locality. Sampling was limited to first 0 to 2.5 m of each tree, and specimens were 

also collected from woody vines and areal roots available within this range. Collecting efforts stopped after 10 minutes passed without encountering new species. 

This “species saturation” time varied significantly between sites. For example, in 

mangrove forests, most of the species were collected before 30 minutes had passed; 

however, in palo colorado and tabonuco forests, 2 hours may have passed without 

reaching species saturation. Specimens were taken to the Multipurpose Laboratory 

at the International Institute of Tropical Forestry and identified using microscopic 

techniques and spot tests (Brodo et al. 2001, Orange et al 2010). Additional identification of difficult taxa was done in laboratory facilities of the Field Museum, Chicago. Information about lichens for each forest type was organized and manipulated 

in Microsoft Excel® tables.6

 PC-ORDTM v. 5.32 (MjM Software Design 1999) was 

used to generate ordinations based on species and genus composition (not presented 

in this report) that helped in visualizing general patterns of community organization 

and revealing factors that may explain variability between forest types.

6

 The use of trade or firm names in this publication is for reader information and does not 

imply endorsement by the U.S. Department of Agriculture of any product or service. 
14

GENERAL TECHNICAL REPORT IITF-GTR-46

Although nonquantitative opportunistic sampling may fail to detect rare, 

inconspicuous, sterile, or cryptic species and therefore may result in an underestimation of the real lichen diversity in these forests (Cáceres et al. 2008), the use of 

this approach in this study is justified mostly because our primary goal is to provide 

a general view of the most conspicuous elements and characteristics of the lichen 

flora of different forest types in Puerto Rico. Nevertheless, we strongly endorse 

additional efforts that use more rigorous quantitative methods to estimate lichen 

diversity in the island. Hopefully, this study will stimulate the formation of new 

initiatives that will move further research in that direction. 

Forest Health and Thelotremoid Lichens

Lichens could potentially provide valuable information about the conservation 

status of tropical forests. A recent study found that the number of morphotypes 

of taxa belonging to thelotremoid Graphidaceae is correlated with different 

levels of ecological continuity in these forests (Rivas-Plata et al. 2008). An 

easy-to-implement sampling protocol, in which thelotremoid lichens are used to 

assess disturbance levels of tropical forest sites based on the Index of Ecological 

Continuity (IEC), was also proposed (Rivas-Plata et al. 2008). In the context of 

their method, IEC could be a measure of morphotype richness depending 

on ecological continuity. 

The method consists of establishing 500-m transects in forest areas to be studied. The number of thelotremoid morphotypes present in a number of trees along 

the transect is recorded. Finally, an IEC is calculated for the forest area studied by 

using the following formula: IEC = 100 × n/Nmax. In this formula, n = number of 

morphotypes per site, and Nmax = maximum expected number of morphotypes per 

site. There are 24 properly described thelotremoid morphotypes (fig. 12). Morphological characters of these morphotypes are described in table 1.

The most critical element of the IEC is the setting of Nmax, which has to be 

adjusted to the forest ecosystem (Rivas-Plata et al. 2008). Although Rivas-Plata 

et al. (2008) provided Nmax values for most of the forest conditions to be found 

between an altitudinal range of 0 to 3500 m in tropical America, the information 

was derived from a dataset from Costa Rica, a continental area not affected by the 

mass elevation effect, a meteorological phenomenon that lowers altitudinal zones 

in island ecosystems (Grubb 1971). Thus, the direct use of Rivas-Plata et al. (2008) 

Nmax values in IEC calculations for forests in Puerto Rico would suppose an 

underestimation of ecological continuity. Altogether, these observations highlight 

the importance of making corrections to Nmax values for insular regions. 

A list of the total number of thelotremoid morphotypes found in the three 

sampled areas for each forest ecosystem treated in this study is presented at the 

The diversity of thelotremoid lichens in a 

forest can provide 

valuable information 

about its conservation 

status.
15

Lichens in Puerto Rico: An Ecosystem Approach

Figure 12—Morphotypes of corticolous thelotremoid lichens.
16

GENERAL TECHNICAL REPORT IITF-GTR-46

Table 1—Morphological characteristics of corticolous thelotremoid lichens (modified from Rivas-Plata 

et al. 2008)

Morphotype Apothecia and reproductive structures Thallusa Genera

Chroodiscoid Open with recurved lobules Smooth, ± shiny Acanthotrema, Chapsa

Leprocarpoid Open with erect lobules Mealy, ± matte Chapsa

Cruentodiscoid Open with erect lobules, disc pigmented Smooth, ± shiny Chapsa

Gyrotremoid Open with recurved lobules, disc, Smooth, ± shiny Gyrotrema

pigmented with concentric rings

Reimnitzioid Open with erect lobules Rough, with crystals Reimnitzia

Glaucescentoid Open with erect lobules Rough, with crystals Leucodecton glaucescens

Leucodectonoid Closed with a tiny pore Rough, with crystals Leucodecton

Leptotremoid Immersed with small pore Rough, with crystals Leptotrema

Myriotremoid Immersed with small pore Smooth, ± shiny Myriotrema (glaucopallens group)

Glaucophaenoid Prominent with wide pore, in section Smooth, ± shiny Myriotrema

with pale walls

Annulotremoid Prominent with wide pore, pore with Smooth, ± shiny Myriotrema, Thelotrema

inner ring

Thelotremoid Prominent with wide pore and inner Smooth, ± shiny Thelotrema

 “mouth”

Ampliotremoid Prominent with wide pore, in section Smooth, ± shiny Ampliotrema, Ocellularia

with black walls

Ocellularioid Prominent with wide pore, pore with Smooth, ± shiny Ocellularia

“finger” (columella), in section with

black walls

Praestantoid Large and prominent with small pore, Smooth, ± shiny Ocellularia (praestans group)

pore with “finger” (columella), in

section with black walls

Rhodostromoid Large and prominent with small pore, Smooth, ± shiny Ocellularia (rhodostroma group)

pore with “finger” (columella), in

section with black walls and pigment

Tenuitremoid Immersed with small pore and black Smooth, ± shiny Clandestinotrema

margin, pore with “finger” (columella),

in section with black walls

Melanotremoid Prominent with wide pore and black Smooth, ± shiny Melanotrema, Ocellularia, 

margin, pore filled with broad “stump” Clandestinotrema, 

(columella), in section with black walls Trinathotrema

Pallidostegoboloid Prominent with wide pore, pore filled Smooth, ± shiny Stegobolus (wrightii group)

with irregular structures, in section 

with pale walls

Stegoboloid Prominent with wide pore, pore filled Smooth, ± shiny Stegobolus

with irregular structures, in section 

with black walls

Redingerioid Immersed with linear slit, slit filled with Smooth, ± shiny Redingeria, Stegobolus

 irregular structures, in section with 

black walls

Isidiotremoid Apothecia lacking, with isidia Smooth, ± shiny Myriotrema, Ocellularia

Schizotremoid Apothecia lacking, with schizidia Smooth, ± shiny Stegobolus

Sorediotremoid Apothecia lacking, with soralia Smooth, ± shiny Myriotrema, Ocellularia

a

 The symbol “±” is used here to mean “more or less.”
17

Lichens in Puerto Rico: An Ecosystem Approach

end of each “Lichen Community” subsection. This information should aid in the 

correct determination of appropriate Nmax values to be used in future IEC calculations for Puerto Rican forests. Suitable Nmax values are fundamental for the 

effective use of the methods proposed by Rivas-Plata et al. (2008) and simplified by 

Mercado-Díaz et al. (N.d).7

Organization and Other Considerations

Each section describing forest types in this report has three main subsections. 

The first, Environment, offers a general description of the physical environment 

of each forest type. This includes information on mean annual temperature, mean 

annual precipitation, and elevation range in which this type of forest is found 

on the island. The second section, Vegetation, aims to briefly illustrate the main 

aspects of vegetation composition and structure in these forests. This information 

is important because vegetation surfaces ultimately provide the substrate on which 

most of the lichen species present in the forest understory grow. The third section 

is titled Lichen Communities; its main purpose is to describe general characteristics of lichen communities in these forests. Information presented in this section 

include (1) observations about the abundance and richness of the different species 

and genera; (2) descriptions of commonly found growth forms, genera and species, 

(3) accounts of species that were found only in some of these forests; and (4) other 

ecological observations concerning the interaction between lichen communities and 

particular forest elements, e.g., lichen species occurrences in particular tree species. 

Each section is supplemented with photographs that illustrate common views of 

forest types and other vegetation attributes found in these forests. 

Bound into the center of this volume is a set of species plates, which contain 

images of the lichen species mentioned in the “Lichen Communities” subsection 

of each forest type. The species names followed by an asterisk (*) indicate that the 

photograph was taken in the field with a high-resolution digital camera. The rest 

of the images were taken with a digital camera mounted on a stereomicroscope. 

To detect the detailed morphological characters shown in these images, and consequently facilitate field identification, the use of a 10× hand lens is recommended. It 

should be noted that photographs taken with the stereomicroscope are of herbarium 

specimens. Specimens in herbarium conditions are dry and usually have less vivid 

colors than species growing in their natural habitats; therefore, care should be taken 

when using these images for identification purposes.

7

 Mercado-Díaz, J.A.; Gould, W.A.; González, G.; Torres-Santana, C. [N.d]. Using lichens 

as indicators of forest health in Puerto Rico. Manuscript in preparation. On file with: J.A. 

Mercado-Díaz, U.S. Department of Agriculture, Forest Service, International Institute of 

Tropical Forestry, Jardin Botanico Sur, 1201 Calle Ceiba, San Juan, PR 00926-1119.
18

GENERAL TECHNICAL REPORT IITF-GTR-46

Note that although lichens were surveyed exhaustively at each site, the number 

of species reported for each ecosystem is not thought to be definitive. Additional 

lichen surveys in other areas will likely increase the number of species for a particular ecosystem. Species richness is reported with the main purpose of offering 

a general view of the diversity of lichens that a person sampling a similar area of a 

particular forest type might find. Likewise, the information related to the species 

and genera found exclusively in a particular ecosystem is tentative. Subsequent field 

surveys in other forests should likely reveal the presence of many of these species 

and genera elsewhere. 

Some information presented throughout this report concerning lichen species 

occurrences in different areas of Puerto Rico and general notes about the island’s 

lichen diversity are personal observations made by Joel A. Mercado-Díaz.

Forests

Puerto Rico has an extremely rich diversity of forests. This diversity could be 

explained by the role that a number of environmental and historical factors have 

had on the ecological processes shaping these ecosystems (Lugo 2005). There are 

numerous schemes that have been used to describe these forests; however, many 

of them lack a comprehensive description of their ecology (Lugo 2005).

The following sections aim to broaden the ecological knowledge of eight forest 

ecosystems of Puerto Rico by presenting information on their abiotic characteristics, vegetation, and lichen communities. These ecosystems are elfin woodland, 

palo colorado forest, sierra palm forest (fig. 13), tabonuco forest, lowland moist 

forest, dry forest, mangrove forest, and Pterocarpus forest. Many ecological aspects 

of these forests and the sampled sites have been described previously (González 

et al. 2007, Gould et al. 2006) and are the object of ongoing ecological research 

(González et al. 2013). 

Elfin Woodland

Environment—

The elfin woodland forest type (fig. 14) occurs within the two wettest Holdridge life 

zones of Puerto Rico, the lower montane wet and rain forests. The elfin woodland 

has an approximate mean annual precipitation of 3908 mm and a mean annual temperature of 19.5 °C (Gould et al. 2006). This forest type occupies very little area in 

Puerto Rico, occurring in a single crescent-shaped band on the windward faces of 

the Luquillo Mountains (Miller and Lugo 2009). The approximate elevation of this 

forest type within El Yunque National Forest is 1010 m (Gould et al. 2006). Owing 

to the superabundance of water, soils are at field capacity much of the year and the 
19

Lichens in Puerto Rico: An Ecosystem Approach

Figure 13—A fire ant walking over a gelatinous-foliose lichen of the genus Leptogium in a sierra 

palm forest, El Yunque National Forest, Puerto Rico.

Figure 14—The understory of an elfin woodland forest in El Yunque National Forest, Puerto Rico.

J.A. Mercado-Díaz J.A. Mercado-Díaz
20

GENERAL TECHNICAL REPORT IITF-GTR-46

total annual runoff (3400 mm) is more than twice the annual rainfall input received 

by most areas of the world (Miller and Lugo 2009). Because the elfin woodland 

ecosystem of Puerto Rico lies entirely within El Yunque National Forest, the whole 

forest type is legally protected.

Vegetation—

The elfin woodland is a closed broad-leaved evergreen forest that generally occurs 

in exposed areas and ridges and is characterized by twisted, gnarled trees that are 

less than 7 m tall, with small diameters, a large number of stems per unit area, 

and extremely slow growth rates (Gould et al. 2006, Miller and Lugo 2009) (fig. 

15). All trees have sclerophyllous leaves that tend to be grouped near the ends of 

the branches (Miller and Lugo 2009). Common trees found in this forest include 

Ocotea spathulata Mez., Eugenia borinquensis Britton, Tabebuia rigida Urb., 

Magnolia splendens Urb., and Clusia rosea Jacq.; whereas rare endemic tree 

species include Ardisia luquillensis (Britton) Alain and Ilex obcordata Sw. var. 

obcordata (Gould et al. 2006, Miller and Lugo 2009). This forest type is also 

characterized by its superabundance of nonvascular epiphytes, particularly mosses 

and liverworts, and the presence of lianas like the endemic Marcgravia sintenisii

Urb. and Mikania cordifolia (L. f.) Willd. (Gould et al. 2006, Lugo 2005). Refer to 

table 2 for common names of plant species identified in this report.

Figure 15—Species of Clandestinotrema growing on an upright branch of a tree in an elfin woodland 

forest, El Yunque National Forest, Puerto Rico.

J.A. Mercado-Díaz
21

Lichens in Puerto Rico: An Ecosystem Approach

Table 2—Common names of plant species identified in this report

Common name in Spanish

Scientific name Common name in English (Puerto Rican usage)

Acrostichum aureum Golden leather fern Palmita del rio

Alchornea latifolia Achiotillo

Ardisia luquillensis Mountain marlberry Mameyuelo

Avicennia germinans Black mangrove Mangle negro

Bourreria succulenta Bodywood Palo de vaca

Bursera simaruba Gumbo limbo Almácigo

Byrsonima wadsworthii Almendrillo

Cecropia schreberiana Pumpwood Yagrumo hembra

Clusia rosea Scotch attorney Cupey

Conocarpus erectus Button mangrove Mangle boton

Cordia borinquensis Capa cimarron

Cyathea arborea West Indian tree fern Helecho arboreo

Cyrilla racemiflora Swamp titi Palo colorado

Dacryodes excelsa Candle tree Tabonuco

Erythroxylum brevipes Brisselet Rocío

Eugenia biflora Blackrodwood Hoja menuda

Eugenia borinquensis Guayabota de sierra

Faramea occidentalis False coffee Cafeillo

Henriettea squamulosum Camasey jusillo

Hippocratea volubilis Medicine vine Bejuco prieto

Hymenaea courbaril Stinkingtoe Algarrobo

Ilex obcordata var. obcordata Cuero de sapo

Inga laurina Sacky sac bean Guama

Ipomoea triloba Little bell Bejuquillo de puerco

Laguncularia racemosa White mangrove Mangle blanco

Magnolia splendens Laurel sabino

Manilkara bidentata Bulletwood Ausubo

Marcgravia sintenisii Shingleplant Pegapalma

Mikania cordifolia Florida Keys hempvine Guaco

Neea buxifolia Saltwood

Ocotea leucoxylon Loblolly sweetwood Laurel geo

Ocotea spathulata Cabalonga cimarrona

Paullinia pinnata Bread and cheese Bejuco de costilla

Prestoea acuminata var. montana Sierran palm Palma de sierra

Pterocarpus officinalis Dragonsblood tree Palo de pollo

Quadrella cynophallophora Jamaican caper Burro prieto

Rhizophora mangle Red mangrove Mangle rojo

Rondeletia portoricensis Juan Tomás

Sloanea berteroana Bullwood Motillo

Spathodea campanulata African tulip tree Tulipán africano

Tabebuia rigida Roble de sierra

Tetragastris balsamifera Masa
22

GENERAL TECHNICAL REPORT IITF-GTR-46

Lichen communities—

Elfin woodlands are characterized for having low species richness of corticolous 

lichens if compared to other forest types in El Yunque National Forest. Only 33 

species have been recorded in sampled areas of this forest type. Nonetheless, these 

forests have the highest number of species within the genus Clandestinotrema, and 

a good representation of taxa belonging to the genus Chapsa. As mentioned before, 

the presence of Clandestinotrema species in Neotropical forests is positively correlated with elevation (Rivas-Plata et al. 2008), which agrees with the observations 

reported here. Competition for space appears to be a major constraint for lichen 

colonization in the elfin woodland as bryophytes are more adapted to the highmoisture conditions found in this ecosystem. 

Although most of the lichen flora in this forest adopts a crustose growth habit, 

it is not uncommon to find species with fruticose or squamulose growth forms, like 

Cladia aggregata (plate 1A) and Cladonia spp., growing on tree branches in the 

understory of this forest type. Foliose lichens are scarce and, if present, are most 

likely cyanobacterial such as species of Leptogium. Dictyonema sericeum (plate 

1B) and Cyphellostereum (plate 1C) are examples of a filamentous basidiolichens

present in these forests. Foliicoulous lichens are uncommon in the understory of 

the elfin woodland forest and nearly all species to be found are close to canopy 

openings.

Some of the most common lichen species found in this forest type include 

Chapsa sp. A (plate 1D), Chapsa thallotrema (plates 1E and 1F), Clandestinotrema 

leucomelaenum (plate 1G), Dictyonema sericeum, Graphis adpressa (plate 1H), 

and Ocellularia rhodostroma (plate 2A). Several species have only been found 

in sampled areas of this forest type. Some of these are Chapsa sp. A, Chapsa sp. 

B (plate 2B), Cladia aggregata, Clandestinotrema analorenae (plate 2C), Clandestinotrema stylothecium (plate 2D), Fissurina crassilabra (plate 2E), Fissurina 

incrustans (plate 2F), and Graphis adpressa.

At least six morphotypes of thelotremoid lichens have been found in elfin 

woodland forests in El Yunque National Forest (Rivas-Plata et al. 2008). These are 

the encountered morphotypes and their representative species:

Leprocarpoid: Chapsa dissuta

Sorediotermoid: Chapsa thallotrema

Tenuitremoid: Clandestinotrema analorenae

Melanotremoid: Clandestinotrema leucomelaenum, C. stylothecium

Rhodostromoid: Ocellularia rhodostroma

Thelotremoid: Thelotrema porinoides
23

Lichens in Puerto Rico: An Ecosystem Approach

An interesting fact from a lichenological perspective is the common sighting of 

free-living Trentepohlia spp., a filamentous green algae hanging from tree branches 

in the elfin woodland forest (fig. 3). Trentepohlia is the most common photobiont 

participating in lichenological associations in tropical ecosystems and is recognized 

by its filamentous growth habit and distinctive orange color, which is caused by the 

presence of carotenoid pigments that mask the green pigments of chlorophyll. In 

lichenized state, Trentepohlia loses its ability to produce carotenoids. Trentepohlia

filaments may also be found in other areas around the island, particularly under 

humid and illuminated conditions.

Palo Colorado Forest

Environment—

The palo colorado forests in Puerto Rico (fig. 16) are considered “mountain wetlands” (Frangi 1983), and according to Holdridge’s system (Ewel and Whitmore 

1973), this forest lies within the subtropical lower montane wet forest (Gould et al. 

2006, Lugo 2005, Miller and Lugo 2009). It occurs in both the eastern and central 

parts of the island up to the summits of some mountains that are above 1000 m 

(Miller and Lugo 2009). The palo colorado forest has a high cloud cover, low illumination, extreme soil saturation, and a high water table (Lugo 2005). Mean annual 

temperature is about 23 °C, and mean annual precipitation reaches about 2932 mm 

(Gould et al. 2006). This forest covers only about 1.2 percent of the island’s total 

Figure 16—The understory of a palo colorado forest in El Yunque National Forest, Puerto Rico.

J.A. Mercado-Díaz
24

GENERAL TECHNICAL REPORT IITF-GTR-46

surface area (Weaver 1987), but encompasses nearly 17 percent of the Luquillo 

Mountains, and grows at elevations higher than 600 m. In El Yunque National 

Forest, these forests are considered cloud forests precisely because cloud condensation commonly starts at this elevation (Lugo 2005).

Vegetation— 

The palo colorado forest is mostly a closed broad-leaved evergreen forest that 

gets its name from the presence of its common tree Cyrilla racemiflora L. (Gould 

et al. 2006) (fig. 17). This forest corresponds to mature vegetation of the zonal 

association in the subtropical lower montane wet forest (Miller and Lugo 2009). 

It is a low-statured forest (3 to 9 m) and, in some places, trees are considerably 

dispersed owing either to high area occupancy of large-diameter trees or because 

environmental conditions limit their density (Lugo 2005). Although the palo 

colorado forest is a closed forest, canopy openings allow light penetration. Clouds 

continuously penetrate the understory, which is considerably open (Lugo 2005). 

The palo colorado forest is poorer in plant species than the adjacent tabonuco 

forests (Miller and Lugo 2009). Common tree species include Cyathea arborea (L.) 

Sm., Prestoea acuminata (Willd.) H.E. Moore var. montana (Graham) A. Hend. & 

G. Galeano, Ocotea spathulata, Alchornea latifolia Sw., among others (Gould et al. 

2006, Lugo 2005). A study classifying vegetation in these forests found about 14 

endemic tree species and six rare native species in the palo colorado forests of El 

Yunque National Forest (Gould et al. 2006). Refer to table 2 for common names of 

plant species.

Figure 17—Lichens are commonly found on aerial roots of trees in the palo colorado forest in El 

Yunque National Forest. In this photo: (A) Coenogonium linkii, and (B) Myeloconis guyanensis.

J.A. Mercado-Díaz

A

B
Plates

Species photographs in plates are organized in the order in which 

they are mentioned in the text. Species names followed by an asterisk (*) indicate that the photograph was taken in the field with a 

high-resolution digital camera. The remainder of the images were 

taken with a digital camera mounted on a stereomicroscope.

Lichens in Puerto Rico: An Ecosystem Approach

25
Plate 1

(A) Cladia aggregata 

(B) Dictyonema sericeum* 

(growing on moss) 

(C) Cyphyellostereum phyllogenum 

(D) Chapsa sp. A 

(E) Chapsa thallotrema* 

(F) Chapsa thallotrema* (detail)

(G) Clandestinotrema leucomelaenum

(H) Graphis adpressa.

Plate 2

(A) Ocellularia rhodostroma 

(B) Chapsa sp. B 

(C) Clandestinotrema analorenae 

(D) Clandestinotrema stylothecium 

(E) Fissurina crassilabra 

(F) Fissurina incrustans 

(G) Coenogonium linkii* 

(H) Herpothallon aurantiacoflavum* (left) 

and Herpothallon granulare* (right).

Plate 3

(A) Herpothallon aurantiacoflavum 

(B) Herpothallon granulare 

(C) Dichosporidium nigrocinctum* 

(D) Dichosporidium nigrocinctum 

(fruiting bodies) 

(E) Graphis rhizocola* 

(F) Malmidea nigromarginata 

(G) Myeloconis guyanensis* 

(H) Ocellularia praestans*

Plate 4

(A) Ocellularia praestans (detail) 

(B) Porina nucula 

(C) Ampliotrema rimosum* 

(D) Arthonia sp. (yellow margin) 

(E) Chapsa alborosella 

(F) Clandestinotrema cf. tenue 

(G) Coenogonium nepalense 

(H) Graphis dimidiata.

Plate 5

(A) Malmidea furfurosa

(B) Malmidea vinosa

(C) Paratopeliopsis caraibica

(D) Ocellularia aff. perforata

(E) Ocellularia cavata

(F) Ocellularia crocea

(G) Ocellularia dolichotata

(H) Ocellularia rhabdospora.

Plate 6

(A) Platythecium grammitis

(B) Sticta sp.*

(C) Leptogium azureum*

(D) Leptogium denticulatum*

(E) Graphis duplicata 

(F) Porina subpungens*

(G) Thelotrema porinoides

(H) Arthonia complanata*.

Plate 7

(A) Graphis proserpens*

(B) Fissurina sp. nov.*

(C) Fissurina sp. nov. (detail)

(D) Megalotremis lateralis

(E) Pyrenula aff. fetivica*

(F) Sticta beauvoisii*

(G) Porina scabrida

(H) Mazosia endonigra.

Plate 8

(A) Herpothallon rubrocinctum*

(B) Phyllopsora buettneri

(C) Phyllopsora corallina*

(D) Usnea sp.*

(E) Stereocaulon ramulosum*

(F) Cladonia subradiata *

(G) Arthonia platygraphidea

(H) Arthothelium distendens.

Plate 9

(A) Ocellularia interposita

(B) Pyrenula macrocarpa

(C) Pyrenula massariospora*

(D) Heterodermia speciosa

(E) Acanthotrema alboisidiatum

(F) Arthonia aff. bessalis

(G) Arthothelium sp. nov

(H) Pseudochapsa dilatata.

Plate 10

(A) Chapsa elabens

(B) Eugeniella sp. nov

(C) Herpothalon aff. pustulata*

(D) Letrouitia vulpina

(E) Leucodecton compuctellum

(F) Malmidea amazonica

(G) Mazosia verrucosa

(H) Megalotremis infernalis.

Plate 11

(A) Ocellularia aff. cavata

(B) Ocellularia ascidiodea

(C) Ocellularia mordenii

(D) Borinquenotrema soredicarpum 

(E) Porina americana

(F) Rhabdodiscus emersellus

(G) Wirthiotrema glaucopallens

(H) Coenogonium leprieurii*.

Plate 12

(A) Physcia atrostriata*

(B) Parmotrema praesorediosum*

(C) Dirinaria purpurascens

(D) Ramalina complanata*

(E) Ramalina peruviana*

(F) Cresponea melanocheiloides*

(G) Cresponea melanocheiloides (detail)

(H) Cryptothecia striata*.

Plate 13

(A) Diorygma poiteai*

(B) Diorygma poiteai (detail)

(C) Hemithecium balbisii*

(D) Hemithecium balbisii (detail)

(E) Graphis glaucescens*

(F) Graphis glaucescens (detail)

(G) Malmidea piperis* 

(H) Malmidea piperis (detail).

Plate 14

(A) Opegrapha bonplandii

(B) Opegrapha dekeselii

(C) Phaeographis brasiliensis

(D) Porina distans*

(E) Porina distans (detail)

(F) Porina conspersa

(G) Pyrenula mamillana

(H) Fissurina subnitens (between 

bark fissures)*.

Plate 15

(A) Fissurina subnitens (detail)

(B) Anisomeridium subprostans

(C) Arthonia aff. pyrrholiza

(D) Arthonia bessalis

(E) Dyplolabia afzelii

(F) Letrouitia domingensis*

(G) Letrouitia domingensis (detail)

(H) Leucodecton bisporum*.

Plate 16

(A) Leucodecton bisporum (detail)

(B) Mazosia carnea

(C) Melanotrema platystomum

(D) Monoblastia borinquensis

(E) Porina tetracerae

(F) Psoroglaena cubensis

(G) Strigula phaea

(H) Trinathotrema stictideum.

Plate 17

(A) Physcia crispa

(B) Physcia sorediosa

(C) Pyxine berteriana

(D) Pyxine eschweileri

(E) Anisomeridium biforme

(F) Arthonia portoricensis

(G) Arthopyrenia majuscula

(H) Bactrospora denticulata.

Plate 18

(A) Graphis furcata

(B) Graphis tenella

(C) Opegrapha cf. varia

(D) Pyrenula quassiaecola

(E) Arthonia antillarum

(F) Arthonia caribaea

(G) Celothelium dominicanum

(H) Coenogonium aurantiacum.

Plate 19

(A) Coenogonium borinquense

(B) Enterographa multilocularis

(C) Fissurina tachygrapha

(D) Leucodecton occultum

(E) Opegrapha astraea

(F) Phaeographis inusta 

(between lenticels)

(G) Phaeographis inusta (detail)

(H) Pyrenula thelomorpha.

Plate 20

(A) Ramonia rappii

(B) Ramonia valenzuelana

(C) Parmotrema endosulphureum

(D) Parmotrema endosulphureum 

(isidia and yellow medulla) 

(E) Physcia erumpens

(F) Pyrenula cerina*

(G) Pyrenula cerina (detail)

(H) Bactrospora myriadea.

Plate 21

(A) Enterographa aff. anguinella

(B) Pyrenula cocoes

(C) Pyrenula ochraceoflava

(D) Pyrenula microcarpa

(E) Herpothallon minimum

(F) Porina curtula

(G) Arthonia aff. rubella

(H) Coenogonium dimorphicum.

Plate 22

(A) Coenogonium portoricense

(B) Crocynia gossypina

(C) Fissurina adscribens

(D) Graphis farinulenta

(E) Diorygma poiteai* (left) and

Graphis farinulenta* (right)

(F) Lecanographa lyncea

(G) Malmidea aff. coralliformis

26 (H) Schismatomma rappii.
27

Plate 1—(A) Cladia aggregata; (B) Dictyonema sericeum* (growing on moss); (C) Cyphyellostereum phyllogenum; (D) Chapsa sp. A; 

(E) Chapsa thallotrema*; (F) Chapsa thallotrema* (detail); (G) Clandestinotrema leucomelaenum; (H) Graphis adpressa.

Plate 1

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-DíazJ.A. Mercado-Díaz J.A. Mercado-Díaz R. Lücking J.A. Mercado-Díaz

A B

C D

E F

G H
28

Plate 2

Plate 2—(A) Ocellularia rhodostroma; (B) Chapsa sp. B; (C) Clandestinotrema analorenae; (D) Clandestinotrema stylothecium; 

(E) Fissurina crassilabra; (F) Fissurina incrustans; (G) Coenogonium linkii*; (H) Herpothallon aurantiacoflavum* (left) and 

Herpothallon granulare* (right).

J.A. Mercado-Díaz

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

R. Lücking

A B

C D

E F

G H
29

Plate 3

Plate 3—(A) Herpothallon aurantiacoflavum; (B) Herpothallon granulare; (C) Dichosporidium nigrocinctum*; (D) Dichosporidium 

nigrocinctum (fruiting bodies); (E) Graphis rhizocola*; (F) Malmidea nigromarginata; (G) Myeloconis guyanensis*; (H) Ocellularia 

praestans*.

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-DíazJ.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

A B

C D

E F

G H
30

Plate 4

Plate 4—(A) Ocellularia praestans (detail); (B) Porina nucula; (C) Ampliotrema rimosum*; (D) Arthonia sp. (yellow margin); 

(E) Chapsa alborosella; (F) Clandestinotrema cf. tenue; (G) Coenogonium nepalense; (H) Graphis dimidiata.

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-DíazJ.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

A B

C D

E F

G H
31

Plate 5

Plate 5—(A) Malmidea furfurosa; (B) Malmidea vinosa; (C) Paratopeliopsis caraibica; (D) Ocellularia aff. perforata; (E) Ocellularia 

cavata; (F) Ocellularia crocea; (G) Ocellularia dolichotata; (H) Ocellularia rhabdospora. J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

A B

C D

E F

G H
32

Plate 6

Plate 6—(A) Platythecium grammitis; (B) Sticta sp*; (C) Leptogium azureum*; (D) Leptogium denticulatum*; (E) Graphis duplicata; 

(F) Porina subpungens*; (G) Thelotrema porinoides; (H) Arthonia complanata*.

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-DíazJ.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

A B

C D

E F

G H
33

Plate 7

Plate 7—(A) Graphis proserpens*; (B) Fissurina sp. nov.*; (C) Fissurina sp. nov. (detail); (D) Megalotremis lateralis; (E) Pyrenula aff.

fetivica*; (F) Sticta beauvoisii*; (G) Porina scabrida; (H) Mazosia endonigra. J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

A B

C D

E F

G H
34

Plate 8

Plate 8—(A) Herpothallon rubrocinctum*; (B) Phyllopsora buettneri; (C) Phyllopsora corallina*; (D) Usnea sp.*; (E) Stereocaulon 

ramulosum*; (F) Cladonia subradiata *; (G) Arthonia platygraphidea; (H) Arthothelium distendens. A. Cuevas-Padró R. Lücking

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-DíazJ.A. Mercado-Díaz J.A. Mercado-Díaz

A B

C D

E F

G H
35

Plate 9

Plate 9—(A) Ocellularia interposita; (B) Pyrenula macrocarpa; (C) Pyrenula massariospora*; (D) Heterodermia speciosa; 

(E) Acanthotrema alboisidiatum; (F) Arthonia aff. bessalis; (G) Arthothelium sp. nov; (H) Pseudochapsa dilatata. J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

A B

C D

E F

G H
36

Plate 10

Plate 10—(A) Chapsa elabens; (B) Eugeniella sp. nov; (C) Herpothalon aff. pustulata*; (D) Letrouitia vulpina; (E) Leucodecton 

compuctellum; (F) Malmidea amazonica; (G) Mazosia verrucosa; (H) Megalotremis infernalis.

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-DíazJ.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

A B

C D

E F

G H
37

Plate 11

Plate 11—(A) Ocellularia aff. cavata; (B) Ocellularia ascidiodea; (C) Ocellularia mordenii; (D) Borinquenotrema soredicarpum; 

(E) Porina americana; (F) Rhabdodiscus emersellus; (G) Wirthiotrema glaucopallens; (H) Coenogonium leprieurii*. J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

A B

C D

E F

G H
38

Plate 12

Plate 12—(A) Physcia atrostriata*; (B) Parmotrema praesorediosum*; (C) Dirinaria purpurascens; (D) Ramalina complanata*; 

(E) Ramalina peruviana*; (F) Cresponea melanocheiloides*; (G) Cresponea melanocheiloides (detail); (H) Cryptothecia striata*.

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-DíazJ.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

A B

C D

E F

G H
39

Plate 13

Plate 13—(A) Diorygma poiteai*; (B) Diorygma poiteai (detail); (C) Hemithecium balbisii*; (D) Hemithecium balbisii (detail); 

(E) Graphis glaucescens*; (F) Graphis glaucescens (detail); (G) Malmidea piperis*; (H) Malmidea piperis (detail). J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

A B

C D

E F

G H
40

Plate 14

Plate 14—(A) Opegrapha bonplandii; (B) Opegrapha dekeselii; (C) Phaeographis brasiliensis; (D) Porina distans*; (E) Porina distans 

(detail); (F) Porina conspersa; (G) Pyrenula mamillana; (H) Fissurina subnitens (between bark fissures)*.

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-DíazJ.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

A B

C D

E F

G H
41

Plate 15

Plate 15—(A) Fissurina subnitens (detail); (B) Anisomeridium subprostans; (C) Arthonia aff. pyrrholiza; (D) Arthonia bessalis; 

(E) Dyplolabia afzelii; (F) Letrouitia domingensis*; (G) Letrouitia domingensis (detail); (H) Leucodecton bisporum*. J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

A B

C D

E F

G H
42

Plate 16

Plate 16—(A) Leucodecton bisporum (detail); (B) Mazosia carnea; (C) Melanotrema platystomum; (D) Monoblastia borinquensis; 

(E) Porina tetracerae; (F) Psoroglaena cubensis; (G) Strigula phaea; (H) Trinathotrema stictideum.

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-DíazJ.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

A B

C D

E F

G H
43

Plate 17

Plate 17—(A) Physcia crispa; (B) Physcia sorediosa; (C) Pyxine berteriana; (D) Pyxine eschweileri; (E) Anisomeridium biforme; 

(F) Arthonia portoricensis; (G) Arthopyrenia majuscula; (H) Bactrospora denticulata. J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

A B

C D

E F

G H
44

Plate 18

Plate 18—(A) Graphis furcata; (B) Graphis tenella; (C) Opegrapha cf. varia; (D) Pyrenula quassiaecola; (E) Arthonia antillarum; 

(F) Arthonia caribaea; (G) Celothelium dominicanum; (H) Coenogonium aurantiacum.

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-DíazJ.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz R. Lücking

A B

C D

E F

G H
45

Plate 19

Plate 19—(A) Coenogonium borinquense; (B) Enterographa multilocularis; (C) Fissurina tachygrapha; (D) Leucodecton occultum; 

(E) Opegrapha astraea; (F) Phaeographis inusta (between lenticels); (G) Phaeographis inusta (detail); (H) Pyrenula thelomorpha. J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

R. Lücking

A B

C D

E F

G H
46

Plate 20

Plate 20—(A) Ramonia rappii; (B) Ramonia valenzuelana; (C) Parmotrema endosulphureum; (D) Parmotrema endosulphureum (isidia 

and yellow medulla); (E) Physcia erumpens; (F) Pyrenula cerina*; (G) Pyrenula cerina (detail); (H) Bactrospora myriadea.

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-DíazJ.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

A B

C D

E F

G H
47

Plate 21

Plate 21—(A) Enterographa aff. anguinella; (B) Pyrenula cocoes; (C) Pyrenula ochraceoflava; (D) Pyrenula microcarpa; 

(E) Herpothallon minimum; (F) Porina curtula; (G) Arthonia aff. rubella; (H) Coenogonium dimorphicum. J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz R. Lücking

A B

C D

E F

G H
48

Plate 22

Plate 22—(A) Coenogonium portoricense; (B) Crocynia gossypina; (C) Fissurina adscribens; (D) Graphis farinulenta; (E) Diorygma 

poiteai* (left) and Graphis farinulenta* (right); (F) Lecanographa lyncea; (G) Malmidea aff. coralliformis; (H) Schismatomma rappii.

J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-DíazJ.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz J.A. Mercado-Díaz

A B

C D

E F

G H
49

Lichens in Puerto Rico: An Ecosystem Approach

Lichen communities—

Along with the tabonuco and lowland moist forests (see below), palo colorado 

forests in El Yunque National Forest are perhaps one of the most lichen-diverse forest ecosystems of Puerto Rico. About 85 species have been found in sampled areas 

of this forest type. Sampled areas of palo colorado forests resulted in the highest 

number of species within the genera Ocellularia, Chapsa, Malmidea, Phyllopsora, 

Rhabdodiscus, and Thelotrema. Species of Ampliotrema, Compositrema, and 

Paratopeliopsis were found only in this forest type (Mercado-Díaz et al., in press). 

Palo colorado forests are second to elfin woodland forests in the number of species 

within the genus Clandestinotrema. This confirms that similar to other forests 

in the Neotropics, species within this genus are limited to high-elevation forests 

(Rivas-Plata et al. 2008).

Filamentous lichens are evident in palo colorado forests in El Yunque National 

Forest, where species like Coenogonium linkii (plate 2G) are occasionally found at 

the base of trees. Basidiolichens are also present in these forests, more commonly 

the species Dictyonema sericeum (plate 1B). Foliose and fruticose lichens are 

mostly absent under the shaded understory; only microfoliose species within the 

genus Phyllopsora may be observed. Several species with byssoid growth habit 

including Herpothallon aurantiacoflavum (plates 2H and 3A), H. granulare (plates 

2H and 3B), and Dichosporidium nigrocinctum (plate 3, C and D) are frequently 

found in these forests. 

Common corticolous species in the palo colorado forest include Chapsa thallotrema (plate 1, E and F), Coenogonium linkii, Dichosporidium nigrocinctum, 

Dictyonema sericeum, Graphis rhizocola (plate 3E), Herpothallon aurantiacoflavum, Malmidea nigromarginata (plate 3F), Myeloconis guyanensis (plate 3G), 

Ocellularia praestans (plates 3H and 4A), and Porina nucula (plate 4B). Many of 

these species can also be found in other ecosystem types in El Yunque National 

Forest.

Several corticolous lichens have been found only in sampled areas of palo 

colorado forests in El Yunque National Forest. Some of these include Ampliotrema 

rimosum (plate 4C), Arthonia spp. (yellow margin) (plate 4D), Chapsa alborosella

(plate 4E), Clandestinotrema cf. tenue (plate 4F), Coenogonium nepalense (plate 

4G), Graphis dimidiata (plate 4H), Malmidea furfurosa (plate 5A), M. vinosa (plate 

5B), Paratopeliopsis caraibica (plate 5C), Ocellularia aff. perforata (plate 5D), O. 

cavata (plate 5E), O. crocea (plate 5F), O. dolichotata (plate 5G), O. rhabdospora

(plate 5H), and Platythecium grammitis (plate 6A). 
50

GENERAL TECHNICAL REPORT IITF-GTR-46

At least 11 morphotypes of thelotremoid lichens have been found in sampled 

areas of palo colorado forests in El Yunque National Forest (Rivas-Plata et al. 

2008). These are the encountered morphotypes and several representative species: 

Ampliotremoid: Ampliotrema rimosum

Chroodiscoid: Chapsa alborosella, Astrochapsa platycarpella

Leprocarpoid: Chapsa dissuta, C. esslingeri

Melanotremoid: Clandestinotrema leucomelaenum

Tenuitremoid: Clandestinotrema cf. tenue

Myriotremoid: Paratopeliopsis caribica

Ocellularioid: Ocellularia crocea, O. perforata, O. tacarcunae

Rhodostromoid: Ocellularia cavata, O. rhodostroma, O. xanthostroma

Praestantoid: Ocellularia praestans, O. rhabdospora, O. dolichotata

Stegoboloid: Rhabdodiscus emersus, R. schizostomus, R. isidiiferus

Thelotremoid: Thelotrema porinoides, T. lepadodes

Sierra Palm Forest

Environment—

In Puerto Rico, the sierra palm forest ecosystem (palm break) is found mostly 

within the lower montane wet forest life zone but might also reach areas classified 

as subtropical wet and subtropical rain forest (fig. 18). This forest type consists of 

nearly pure stands of Prestoea acuminata var. montana (Gould et al. 2006, Miller 

and Lugo 2009). Palm forest stands have a mean annual temperature of 20.7 °C and 

a mean annual precipitation of 3956 mm. These forests may cover nearly 11 percent 

Figure 18—The understory of a sierra palm forest in El Yunque National Forest, Puerto Rico.

J.A. Mercado-Díaz
51

Lichens in Puerto Rico: An Ecosystem Approach

of the Luquillo Mountains (Gould et al. 2006, Miller and Lugo 2009, Weaver 2012). 

Some of the characteristics of the “palm break” include its high dominance and a 

sharp ecotone with adjacent associations (Miller and Lugo 2009). The sierra palm 

forest is present in the 730 to 915 m altitudinal zone and can be found frequently 

interspersed with palo colorado and tabonuco forests in El Yunque National Forest 

(Miller and Lugo 2009). 

Vegetation—

Plant communities of the sierra palm forest are mostly found in azonal, steeply 

sloping sites dominated by P. acuminata var. montana and are characterized by 

having a high abundance of epiphytes (Gould et al. 2006) (fig. 19). The development 

of an understory in the sierra palm forest is poor and occasionally absent. Soils 

are periodically covered by herbaceous vegetation and mosses (Lugo 2005). Five 

endemic tree species with diameter at breast height > 2 cm are commonly found 

in sierra palm forests in El Yunque National Forest, the most abundant being 

Henriettea squamulosum (Cogn.) W.S. Judd, Eugenia borinquensis, and Cyathea 

arborea (L.) Sm. (Gould et al. 2006). The abundance of Cecropia schreberiana

Figure 19—Patches of the common crustose lichen Chapsa thallotrema in El Yunque National Forest, growing on the trunk of 

Prestoea acuminata var. montana in a sierra palm forest.

J.A. Mercado-Díaz
52

GENERAL TECHNICAL REPORT IITF-GTR-46

Miq. in the sierra palm forest is indicative of past hurricane disturbance (Gould et 

al. 2006). When occurring in the tabonuco forest, P. acuminata var. montana does 

not form any particular association in the forest canopy and is frequently found in 

the understory and in microenvironments that are water-saturated (Lugo 2005). 

See table 2 for common names of plant species.

Lichen communities—

Perhaps the most distinctive characteristic of the sierra palm forest in terms of its 

lichen flora is that it has the lowest species diversity compared to the rest of the 

forest types in El Yunque National Forest. Only 24 species have been found in 

sampled areas of this forest type. Despite its low species diversity, lichens in the 

sierra palm forest are usually more evident than in other forest types of El Yunque 

National Forest owing to the frequent occurrence of foliose lichens on tree trunks. 

For example, species in the genus Sticta (plate 6B) were mostly observed within 

this forest type. Many species of Leptogium, such as L. azureum (plate 6C) and 

L. denticulatum (plate 6D), are commonly found in the sierra palm forests. The 

new species Thalloloma rubromarginatum has been found only in this forest type 

(Mercado-Díaz et al., in press).

Most of the lichen flora in palm forests is crustose. Coenogonium linkii (plate 

2G) is an example of filamentous species found in these forests. Byssoid growth 

forms are represented by species of Herpothallon, like H. granulare (plates 2H 

and 3B). 

Some of the most commonly encountered lichen species of the sierra palm 

forest are Chapsa thallotrema (plate 1, E and F), Coenogonium linkii, Graphis 

duplicata (plate 6E), Herpothallon granulare, Leptogium azureum, Porina 

subpungens (plate 6F), and Thelotrema porinoides (plate 6G). Several of these 

species may also be found in other ecosystem types in El Yunque National Forest. 

Only a few species have been found exclusively in sampled areas of this forest 

type. Some of these include Arthonia complanata (plate 6H), Graphis proserpens

(plate 7A), Fissurina sp. nov. (plate 7, B and C), Megalotremis lateralis (plate 7D), 

Pyrenula aff. fetivica (plate 7E), and Sticta beauvoisii (plate 7F).

Only two morphotypes of thelotremoid lichens have been found in sampled 

areas of sierra palm forests in El Yunque National Forest (Rivas-Plata et al. 2008). 

These are the encountered morphotypes and their representative species: 

Sorediotremoid: Chapsa thallotrema 

Thelotremoid: Thelotrema porinoides

It is interesting, from an ecological perspective, that most of the corticolous 

lichens occurring in sierra palm forests grow on the trunks of tree species other 
53

Lichens in Puerto Rico: An Ecosystem Approach

than P. acuminata var. montana, which is the dominant tree in this ecosystem. 

Nonetheless, specimens of P. acuminata var. montana present in other forest types 

of El Yunque National Forest apparently have higher species diversity on their 

trunks than specimens occurring in pure sierra palm forest stands (table 3). A 

possible explanation for this phenomenon is that trees with high species diversity 

surrounding P. acuminata var. montana individuals in these other forests are facilitating the immigration of species to neighboring P. acuminata var. montana trees. 

Table 3—Lichens that grow on Prestoea acuminata var. montana trees in 

different forest types in El Yunque National Forest, Puerto Rico

Species Elfin Palo colorado Sierra palm Tabonuco

Chapsa thallotrema X X X X

Chapsa alborosella X

Dichosporidium nigrocinctum X

Graphis duplicata X X

Herpothallon rubrocinctum X

Mazosia ocellata X

Ocellularia sp. X

Ocellularia sp. A X

Porina scabrida X

Pyrenula aspitea X

Pyrenula sp. A X

Sterile crustose X

Thelotrema porinoides X

 Total 1 3 3 10

Tabonuco Forest

Environment— 

The tabonuco forest type occurs mainly in mid- to high-elevation areas of Puerto 

Rico and its elevational range spans from 15 to 550 m (Brown et al. 1983) (fig. 20). 

Nonetheless, in mountains like those in Tres Picachos State Forest in Jayuya, this 

forest may be found at 800 m (Lugo 2005). This ecosystem is characterized by 

having high tree-species diversity per unit area (Gould et al. 2006) and the presence 

of tall broadleaf evergreen hardwood trees that commonly exhibit buttressed 

trunks (Miller and Lugo 2009). It harbors a diverse epiphyte flora and many 

species of lianas. Many of the plants present in the tabonuco forest exhibit drip-tip 

leaves. It has a mean annual precipitation of 3060 mm per year and a mean annual 

temperature of 23 °C (Gould et al. 2006). Water deficits in the tabonuco forest are 

very small and soil moisture usually drops below field capacity (Miller and Lugo 

2009).
54

GENERAL TECHNICAL REPORT IITF-GTR-46

Vegetation—

The tabonuco forest is a closed broad-leaved forest that 

gets its name from its dominant tree, Dacryodes excelsa

Vahl (fig. 21). Forest patches of this ecosystem in El 

Yunque National Forest could harbor about 40 tree species and about 86 plant species (Gould et al. 2006). These 

forests form a complete canopy at about 20 m. Other 

prominent species are Sloanea berteriana Choisy ex DC, 

Manilkara bidentata (A. DC.) A. Chev, and Tetragastris 

balsamifera (Sw.) Oken (Gould et al. 2006, Lugo and 

Miller 2009). After disturbances, Cecropia schreberiana 

invades open areas and rapidly closes the canopy. This 

forest type includes several rare endemic species like 

Cordia borinquensis Urb., Rondeletia portoricensis Krug. 

& Urb., and Byrsonima wadsworthii Little (Gould et al. 

2006). Along with the palo colorado forest, the tabonuco 

forest has the highest number of native plant species per 

unit area (Gould et al. 2006). Lugo (2005) reported that 

the tabonuco forest has high populations of “microscopic 

fungi” colonizing leaf surfaces in the canopy. Most of these microscopic fungi are 

possibly foliicolous lichens that have been observed growing along with liverworts 

on the leaves of these forests. See table 2 for common names of plant species.

Figure 21—Mosaic of lichens growing on the lower trunk of a tree in a tabonuco forest. El Yunque 

National Forest, Puerto Rico.

Figure 20—The trunk and sap of Dacryodes excelsa in El 

Yunque National Forest. This trunk is almost completely 

covered with a greenish crustose lichen.

J.A. Mercado-Díaz

J.A. Mercado-Díaz
55

Lichens in Puerto Rico: An Ecosystem Approach

Lichen communities—

Tabonuco forests have one of the richest lichen biota in Puerto Rico, with at least 

76 corticolous species recorded in sampled areas of this forest type in El Yunque 

National Forest. Perhaps because D. excelsa is a dominant element in these forests, 

it appears to be the tree species with the highest number of lichen taxa on its bark. 

There are at least 27 known species growing on the lower trunk sections of D. 

excelsa (see list below). Although not as conspicuous as D. excelsa, tree individuals 

of Prestoea acuminata var. montana are often found with several lichen species 

such as Dichosporidium nigrocinctum (plate 3, C and D), Porina scabrida (plate 

7G), Graphis duplicata (plate 6E), and Mazosia endonigra (plate 7H). These forests 

also possess the highest number of Porina and Herpothallon species for any forest 

type discussed in this report. Species of Acanthotrema and Borinquenotrema have 

only been found in this forest type (Mercado-Díaz et al., in press).

Lichens that grow on D. excelsa trees in El Yunque National Forest, Puerto Rico:

Acanthotrema alboisidiatum

Arthonia aff. bessalis

Bacidia sp. A

Chapsa thallotrema

Dichosporidium nigrocinctum

Herpothallon aurantiacoflavum

Herpothallon rubrocinctum

Leucodecton compunctelum

Mazosia sp. A

Mazosia sp. B

Mazosia sp. nov.

Myeloconis guyanensis

Myriotrema sp. B

Ocellularia cf. praestans

Ocellularia mordenii

Ocellularia sp. D (sorediate)

Ocellularia umbilicata

Opegrapha sp. A

Phyllopsora sp. A

Phyllopsora buettneri

Porina (sterile)

Porina conspersa

Pyrenula macrocarpa

Pyrenula mastophoroides

Pyrenula fetivica

With the exception of occasional foliose lichens in upper canopy layers, nearly 

all lichen taxa documented in these forests are crustose. Several species with 

byssoid growth habit are commonly found; e.g., D. nigrocinctum, Herpothallon 

aurantiacoflavum (plates 2H and 3A), H. rubrocinctum (plate 8A), and H. granulare

(plates 2H and 3B). Squamulose species are represented by several species of Phylopsora, like P. buettneri (plate 8B), P. corallina (plate 8C), and the basidiolichen 

Cyphellostereum (plate 1C). Fruticose lichens are absent in the understory, although 

species of Usnea (plate 8D) can be found in light-exposed conditions. Dimorphic 

species, like those in the genus Cladonia (e.g. Cladonia subradiata, plate 8F) are 

expected to be found in open areas in these forests, growing directly on the soil or 

on other exposed substrates; however, these have not yet been encountered.
56

GENERAL TECHNICAL REPORT IITF-GTR-46

Common lichen species within this forest type include Arthonia platygraphidea

(plate 8G), Arthothelium distendens, (plate 8H), Chapsa thallotrema (plate 2, E 

and F), Ocellularia interposita (plate 9A), Mazosia endonigra (plate 7H), Pyrenula 

macrocarpa (plate 9B), and Pyrenula massariospora (plate 9C). Some of these 

species may also be found in other ecosystem types in El Yunque National Forest 

and even in forests at lower elevations. Corticolous species of more exposed 

conditions or occurring in the canopy include Thelotrema porinoides (plate 6G) 

and Heterodermia speciosa (plate 9D). Several species have only been found 

in sampled areas of this forest type; for example: Acanthotrema alboisidiatum

(plate 9E), Arthonia aff. bessalis (plate 9F), Arthothelium sp. nov. (plate 9G), 

Pseudochapsa dilatata (plate 9H), Chapsa elabens (plate 10A), Eugeniella sp. 

nov. (plate 10B), Herpothallon aff. pustulata (plate 10C), Letrouitia vulpina (plate 

10D), Leucodecton compuctellum (plate 10E), Malmidea amazonica (plate 10F), 

Mazosia verrucosa (plate 10G), Megalotremis infernalis (plate 10H), Ocellularia

aff. cavata (plate 11A), O. ascidioidea (plate 11B), O. mordenii (plate 11C), 

Borinquenotrema soredicarpum (plate 11D), Porina americana (plate 11E), P. 

scabrida, Rhabdodiscus emersellus (plate 11F), and Wirthiotrema glaucopallens 

(plate 11G).

Tabonuco forests have the second highest diversity of thelotremoid lichens 

documented in El Yunque National Forest (compared to palo colorado forests). In 

this respect, at least nine morphotypes of thelotremoid lichens have been found 

(Rivas-Plata et al. 2008). The most numerous genus of thelotremoid lichens in this 

forest is Ocellularia with 12 species. These are the encountered morphotypes and 

several representative species: 

Leprocarpoid: Pseudochapsa dilatata

Sorediotremoid: Chapsa thallotrema

Leucodectonoid: Leucodecton compunctellum

Myriotremoid: Myriotrema sp. nov., Wirthiotrema glaucopallens

Ocellularioid: Ocellularia ascidiodea, O. perforata, O. umbilicata

Rhodostromoid: Ocellularia mordenii, O. aff. cavata

Praestantoid: Ocellularia cf. praestans, O. interposita

Stegoboloid: Rhabdodiscus emersus, R. emersellus

Thelotremoid: Thelotrema porinoides
57

Lichens in Puerto Rico: An Ecosystem Approach

Lowland Moist Forest

Environment—

The lowland moist forest occurs in the lowland subtropical moist Holdridge life 

zone (Ewel and Whitmore 1973) (fig. 22). It covers more area than any of the other 

life zones described by Ewel and Whitmore (1973). Mean annual rainfall in the 

lowland moist forest varies from 1000 to 2200 mm and mean annual temperature 

is about 27.5 °C (Gould et al. 2006, Miller and Lugo 2009). This forest type occurs 

in a variable elevation range, from sea level to 671 m (Ewel and Whitmore 1973). 

Throughout the world, lowland moist forests are among the most intensively 

used life zones (Ewel and Whitmore 1973). In Puerto Rico, most of these forests 

were deforested in the past mainly because their climatic conditions are favorable 

for agricultural activities (Miller and Lugo 2009). Other forest ecosystems, like 

Pterocarpus wetlands and mangrove swamps, could be classified as lowland moist 

forests; however, their unique biological and environmental characteristics justify a 

separate formal description (see further sections).

Figure 22—A tree of Spathodea campanulata, a fast-growing species commonly observed in lowland 

moist forests in Puerto Rico.

Vegetation—

This forest is characterized by trees up to 20 m tall with rounded crowns (Miller and 

Lugo 2009) (fig. 23). Dominant canopy vegetation includes several tree species such 

as Manilkara bidentata, Ocotea leucoxylon (Sw.) De Laness. and Hymenaea courbaril L. (Gould et al. 2006). Faramea occidentalis (L.) A. Rich. and Inga laurina

J.A. Mercado-Díaz
58

GENERAL TECHNICAL REPORT IITF-GTR-46

(Sw.) Willd. are common understory species (Gould et al. 2006). These forests also 

have the highest mean number of nonnative plant species per unit area (Gould et 

al. 2006). Epiphytes are common but rarely cover the surface of branches and trees 

entirely (Miller and Lugo 2009). Many of the woody species are deciduous during the dry season (Miller and Lugo 2009). Because most of this forest type was 

subjected to intensive human use in the past, it is extremely difficult to find natural 

undisturbed stands.

Lichen communities—

Although most lowland moist forests in Puerto Rico have been subject to intense 

human alteration, these areas may be among the forest ecosystems with the highest 

number of lichen species on the island. At least 86 species of corticolous lichens 

were identified in the understory of these forests. These forests also exhibit the 

highest number of lichen genera represented in a forest type (37). Because lowland 

moist forests occupy most of the island’s surface area (59 percent) (Miller and Lugo 

2009), and include other interesting vegetation associations occurring in serpentineand limestone-derived soils not discussed in this report, lichen species richness of 

these forests should be higher than that reported here. 

Figure 23—Trunk of a tree in lowland moist forest. To the right, two thalli of Cryptothecia striata. 

Río Piedras, Puerto Rico.

J.A. Mercado-Díaz
59

Lichens in Puerto Rico: An Ecosystem Approach

The lichen biota of lowland moist forests in Puerto Rico is almost completely 

dominated by crustose growth forms. Filamentous growth forms may occasionally 

be found on the base of trunks, particularly the species Coenogonium leprieurii

(plate 11H) and Coenogonium linkii (plate 2G). Foliose growth forms are rarely 

found in the shaded understory of these forests; however, several species such 

as Physcia, Pyxine, and Parmotrema have been seen on fallen canopy branches, 

indicating their presence in upper canopy layers. Physcia atrostriata (plate 12A), 

Parmotrema praesorediosum (plate 12B), and Dirinaria purpurasens (plate 12C) 

are commonly observed foliose lichens in marginal areas of these forests. Fruticose 

lichens like the species Ramalina complanata (plate 12D) and Ramalina peruviana

(plate 12E) are occasionally observed in open areas of these forests.

Compared to other forest ecosystems presented here, lowland moist forests may 

have the highest diversity of species in the genera Fissurina and Opegrapha. Commonly encountered species of these forests include Cresponea melanocheiloides

(plate 12, F and G), Cryptothecia striata (plate 12H), Diorygma poiteai (plate 13, 

A and B), Hemithecium balbisii (plate 13, C and D), Graphis glaucescens (plate 13, 

E and F), Malmidea piperis (plate 13, G and H), Opegrapha bonplandii (plate 14A), 

Opegrapha dekeselii (plate 14B), Phaeographis brasiliensis (plate 14C), Porina 

distans (plate 14, D and E), Porina conspersa (plate 14F), Pyrenula mamillana

(plate 14G), and Fissurina subnitens (plates 14H and 15A). 

Species that were only found in these forests include Anisomeridium 

subprostans (plate 15B), Arthonia aff. pyrrholiza (plate 15C), Arthonia bessalis

(plate 15D), Coenogonium leprieurii, Cresponea melanocheiloides, Dyplolabia 

afzelii (plate 15E), Letrouitia dominguensis (plate 15, F and G), Leucodecton 

bisporum (plates 15H and 16A), Mazosia carnea (plate 16B), Melanotrema 

platystomum (plate 16C), Monoblastia borinquensis (plate 16D), Porina tetracerae 

(plate 16E), Psoroglaena cubensis (plate 16F), Strigula phaea (plate 16G), and 

Trinathotrema stictideum (plate 16H).

There are at least five morphotypes of thelotremoid lichens present in sampled 

areas of lowland moist forests. These are the encountered morphotypes and their 

representative species: 

Leprocarpoid: Chapsa defecta

Sorediotremoid: Chapsa thallotrema

Leucodectonoid: Leucodecton bisporum

Melanotremoid: Melanotrema platystomum, Trinathotrema stictideum

Glaucophaenoid: Myriotrema erodens
60

GENERAL TECHNICAL REPORT IITF-GTR-46

Dry Forest

Environment—

Dry forests have the highest temperatures and lowest precipitation of all forest ecosystems in Puerto Rico and are found within the subtropical dry forest zone (Ewel 

and Whitmore 1973) (fig. 24). These forests cover vast areas in southwestern Puerto 

Rico, offshore islands like Mona, Culebra, Vieques, Caja de Muertos, Desecheo, 

and smaller areas to the east around the vicinity of Fajardo (Lugo 2005, Miller and 

Lugo 2009). Dry forests mostly occur along the coast and their elevation spans 

from sea level to about 200 m (Lugo 2005). Because mean annual rainfall ranges 

from 600 to 1100 mm, water scarcity is the predominant environmental condition 

in these forests (Lugo 2005, Miller and Lugo 2009). Dry forest air temperatures can 

be extremely variable during the day, occasionally reaching more than 30 °C (Lugo 

2005). Most dry forests in Puerto Rico occur on calcareous substrates, and their 

mean annual temperature is about 25 °C (Lugo 2005). Noncalcareous dry forests 

cover a smaller area (about 1.2 percent of the island) and their mean annual temperature might be slightly higher than calcareous dry forests (27.5 °C) (Gould 

et al. 2006, Lugo 2005).

Vegetation—

Vegetation of dry forest areas visited for this project is typical of dry forests occurring in noncalcareous substrates (fig. 25). Commonly encountered tree species 

include Bursera simaruba (L.) Sarg., Bourreria succulenta Jacq., Quadrella 

Figure 24—The understory of a dry forest. Former Naval Station Roosevelt Roads, Ceiba, Puerto 

Rico.

J.A. Mercado-Díaz
61

Lichens in Puerto Rico: An Ecosystem Approach

cynophallophora (L.) Hutch., Erythroxylum brevipes 

DC., Neea buxifolia (Hook. f.) Heimerl, and Eugenia 

biflora (L.) DC. (Gould et al. 2006). Plant species 

diversity per unit area was the highest (99 species per 

300 m2

) among several forest ecosystems (Gould et al. 

2006). Evergreen species are predominant and there is 

low dominance of deciduous species compared to dry 

forests occurring on calcareous substrates (Lugo 2005). 

In calcareous dry forests, soils accumulate little water 

because of their rocky nature and shallowness, creating 

arid conditions for plant growth (Lugo 2005). In this 

respect, plants in noncalcareous dry forests exhibit 

less extreme xeromorphic traits than their counterparts 

in calcareous dry forests. Overall, vegetation of the 

island’s dry forests tends to form a complete ground 

cover and is mostly semideciduous on most soils 

(Miller and Lugo 2009). See table 2 for common 

names of plant species.

Lichen communities—

A total of 77 species of corticolous lichens has been found in sampled areas of this 

forest ecosystem. This suggests that, compared to other lowland forest ecosystems, 

these forests are among the richest in terms of their corticolous lichen biota. Trees 

of dry forests in the southwestern portion of the island have also been seen to contain high lichen cover and diversity. Southwestern dry forests have slightly different 

vegetation composition owing in part to the calcareous nature of their substrate and 

are therefore expected to vary in terms of their lichen composition. Although dry 

forests on calcareous substrates were not sampled for this work, it is suspected that, 

if taken into consideration, dry forests as a whole may contain the highest species 

diversity for any lowland ecosystem of the island.

As in other forest ecosystems, dry forests are dominated by crustose growth 

forms. Several foliose species are occasionally found, such as Physcia crispa

(plate 17A), Physcia sorediosa (plate 17B), Physcia atrostriata (plate 12A), Pyxine 

berteriana (plate 17C), Pyxine eschweileri (plate 17D), and Parmotrema praesorediosum (plate 12B). Although fruticose species were not found, species such as 

Ramalina complanata (plate 12D) have been observed in similar forests around the 

region. Many lichens found in these forests are whitish or brightly colored (yellow, 

orange, etc.). This is a common characteristic exhibited by lichens growing in dry 

environments with high light exposure (Brodo et al. 2001).

Figure 25—Trunk of a tree in a dry forest. Note the mosaic of 

crustose lichens in the trunk. Former Naval Station Roosevelt 

Roads, Ceiba, Puerto Rico.

J.A. Mercado-Díaz
62

GENERAL TECHNICAL REPORT IITF-GTR-46

Dry forests were found to have the highest diversity of species in the genera 

Arthonia, Bactrospora, Physcia, and Pyrenula. Ramonia species were only found 

in these forests. Some of the most common corticolous lichens found in these 

forests are Anisomeridium biforme (plate 17E), Arthonia portoricensis (plate 

17F), Arthopyrenia majuscula (plate 17G), Bactrospora denticulata (plate 17H), 

Graphis furcata (plate 18A), Graphis tenella (plate 18B), Mazosia endonigra

(plate 7H), Opegrapha cf. varia (plate 18C), Porina nucula (plate 4B), Pyrenula 

quassiaecola (plate 18D), and Arthonia antillarum (plate 18E). Among the species 

that have only been found occurring in these forests are Arthonia caribaea (plate 

18F), Celothelium dominicanum (plate 18G), Coenogonium aurantiacum (plate 

18H), Coenogonium borinquense (plate 19A), Enterographa multilocularis (plate 

19B), Fissurina tachygrapha (plate 19C), Graphis tenella, Leucodecton occultum

(plate 19D), Opegrapha astraea (plate 19E), Phaeographis inusta (plate 19, F and 

G), Pyrenula telomorpha (plate 19H), Ramonia rappi (plate 20A), and Ramonia 

valenzuelana (plate 20B).

Only two morphotypes of thelotremoid lichens were found in sampled areas 

representative of dry forests. These are the encountered morphotypes and their 

representative species: 

Leucodectonoid: Leucodecton occultum

Sorediotremoid: Sorediate crustose lichen, possibly Chapsa

Mangrove Forest

Environment—

Mangrove forests grow near sea water and are found at lowland elevations (<5 

m) within the lowland subtropical dry and moist Holdridge life zones (Ewel and 

Whitmore 1973) (fig. 26). Mean annual temperature is 27.3 °C and mean annual 

precipitation is 1414 mm (Gould et al. 2006). Mangrove forests are often referred to 

as tidal “fringing forests” because they thrive in an ecotonal fringe along protected 

tropical coasts, lagoons, bays, and offshore islands (Miller and Lugo 2009). Because 

salt water can flow upstream from estuaries to rivers, mangroves may extend kilometers inland, as far as the presence of salt water occurs (Miller and Lugo 2009). 

By 1975, about half of the mangrove forests of Puerto Rico had been destroyed by 

agricultural activities and other human activities along the coast. In the last few 

years, there has been a net gain in mangrove coverage as a result of their protected 

status (Martinuzzi et al. 2009, Miller and Lugo 2009). Mangrove areas are the most 

extensive estuarine forested wetlands. The largest (Bosque de Pinoñes) is just east 

of San Juan in the municipalities of Carolina and Loíza (Miller and Lugo 2009).
63

Lichens in Puerto Rico: An Ecosystem Approach

Vegetation—

There are four common mangroves species typical to Puerto Rico and the Caribbean: Rhizophora mangle L., Avicennia germinans (L.) L., Laguncularia racemosa

(L.) C.F. Gaertn., and Conocarpus erectus L. (fig. 27). These forests are typically 

found as Rhizophora mangle–dominated stands on coastal and estuarine fringes 

and in basins as pure or mixed stands of A. germinans and L. racemosa (Gould et 

al. 2006). When found in the subtropical moist forest life zone, mangroves appear to 

grow taller than in the subtropical dry life zone (Miller and Lugo 2009). Mangrove 

forests have the lowest plant species diversity per unit area as compared to other 

plant communities in Puerto Rico, although most of their flora is native (Gould et 

al. 2006). Mangrove is a general term that can refer to numerous families, genera, 

and species in totally different taxons (Miller and Lugo 2009). All plant species 

occurring in mangrove forests are salt-tolerant, or “halophytes.” Mangroves provide 

a safe wildlife habitat both on land and around their prop roots in water, dampen the 

power of storm waves, and help stabilize land that normally would be eroded to the 

sea. See table 2 for common names of plant species.

Lichen communities—

In terms of their lichen composition, mangrove forests along the coastline are perhaps the most species-poor forest ecosystems of the island. Only 18 lichen species 

have been identified in sampled areas of these forests. However, if inland mangrove 

Figure 26—View of the forest floor in a mangrove forest. Trees, saplings, and pneumatophores of 

Avicennia germinans. Ceiba, Puerto Rico.

J.A. Mercado-Díaz
64

GENERAL TECHNICAL REPORT IITF-GTR-46

forest systems are included, species diversity increases substantially. For example, 

one mangrove stand in Sabana Seca Naval Station alone has about 30 corticolous 

lichen species. A possible explanation for the higher species diversity observed in 

inland mangrove forests is that these forests are often close to other species-rich 

forest ecosystems that may be actually serving as a source of new species to these 

mangrove forests. For instance, the mangrove stand in the Sabana Seca Naval Station is only several meters away from a Pterocarpus forest. 

Similar to other forest ecosystems, species with a crustose growth habit dominate in these ecosystems. Foliose species such as Parmotrema endosulphureum

(plate 20 C and D) and Physcia erumpens (plate 20E) are occasionaly found. 

Fruticose growth forms are rare or absent in the understory of these forests. 

The most conspicuous lichen element in these forests is the ubiquitous presence 

of Pyrenula cerina (plate 20F), growing almost exclusively on the trunk and aereal 

roots of R. mangle. Other species associated with P. cerina and commonly found in 

Figure 27—Several trunks of young mangrove trees. Orange color patches belong to Pyrenula cerina, a common crustose lichen found 

in these forests. Las Cabezas de San Juan Natural Reserve, Fajardo, Puerto Rico.

J.A. Mercado-Díaz
65

Lichens in Puerto Rico: An Ecosystem Approach

these forests include Arthonia antillarum (plate 18E), Arthonia portoricensis (plate 

17F), and Bactrospora myriadea (plate 20H). The species Enterographa aff. anguinella (plate 21A), Pyrenula cocoes (plate 21B), Pyrenula ochraceoflava (plate 21C), 

Pyrenula cerina, and Pyrenula microcarpa (plate 21D) are commonly observed and 

have only been found occurring in these forests. Species in the genus Graphis have 

also been observed in mangrove forests.

No thelotremoid lichens were found during fieldwork for this study. Only 

sorediotremoid morphotypes (Rivas-Plata et al. 2008) are expected to be found in 

some mangrove forests of Puerto Rico. Although mangrove forests are not treated 

in Rivas-Plata et al. (2008), if their methods were to be applied for estimating ecological continuity, it can be predicted that even old, undisturbed mangrove forests 

around the island would be classified as “anthropogenic vegetation.” These facts 

highlight the importance of identifying suitable bioindicators of ecological continuity for this type of forest. 

Pterocarpus Forest

Environment—

Pterocarpus forests occur in relict patches within the lowland subtropical moist 

Holdridge life zone (Ewel and Whitmore 1973) (fig. 28). They are mostly found 

on undisturbed freshwater, seasonally flooded, noncalcareous alluvial substrates 

(Gould et al. 2006). Pterocarpus wetlands commonly occur along the coast, 

although a few populations are present along streams in northeastern Puerto 

Rico (Alvarez-López 1990). Compared to mangrove and dry forests, Pterocarpus 

forests have slightly lower temperatures (mean annual temperature = 26.4 °C) and 

higher precipitation (mean annual precipitation = 1685 mm) (Gould et al. 2006). 

These forests occur in the most heavily populated coastal plain and are subject to 

disturbance from changes in the hydrologic regime, particularly those related to 

urban development (Gould et al. 2006). Pterocarpus forests were likely much more 

extensive on coastal plains and along riparian corridors prior to deforestation for 

agricultural activities. 

Vegetation—

Most Pterocarpus forests are considered palustrine forested swamps that usually 

have more than 40 percent of their area in tree cover (Miller and Lugo 2009) (fig. 

29). It is typically a monoculture of the tree species P. officinalis Jacq., which 

occupies the overstory and the fern Acrostichum aureum L. in the understory. 

Like mangrove forests, Pterocarpus forests have low plant species diversity, but 

most of their flora is composed of native species (Gould et al. 2006). Pterocarpus 

trees may occasionally be found among mangrove trees as part of floodplain forests 

in riverine estuaries (Miller and Lugo 2009). Common lianas found here include 
66

GENERAL TECHNICAL REPORT IITF-GTR-46

Figure 28—Trunk and buttressed roots of a Pterocarpus officinalis tree. Sabana Seca Naval Station, Toa Baja, Puerto Rico.

Figure 29—Patches 

of crustose lichens 

growing on young 

Pterocarpus officinalis

trees. Sabana Seca 

Naval Station, Toa 

Baja, Puerto Rico.

J.A. Mercado-Díaz

J.A. Mercado-Díaz
67

Lichens in Puerto Rico: An Ecosystem Approach

Ipomoea triloba L., Paullinia pinnata L., and Hippocratea volubilis L. Freshwater 

Pterocarpus communities exhibit great canopy heights, with trees reaching more 

than 34 m (Gould et al. 2006). As a result of former agricultural activities and 

other coastal development, Pterocarpus forests have been reduced to only a few 

remnant stands. It is believed that in Puerto Rico these forests occupy no more than 

5 percent of their original range, making them deserving of special protection status 

(Miller and Lugo 2009).

Lichen communities—

Pterocarpus forests are almost entirely a monoculture of P. officinalis; therefore, 

most of the corticolous lichens found in these forests grow on the trunk of this tree 

species. Compared to other forest ecosystems, corticolous lichen species richness is 

moderate, with about 59 species found in sampled areas of this forest type. Lichens 

of Pterocarpus forests share some similarities with the lichen flora of lowland moist 

forests, particularly at the genus level. This is not surprising, as both forest types 

are found within the lowland subtropical moist Holdridge life zone (see above).

With the exception of fruticose lichens, most lichen growth forms are represented in these forests. As other forests, crustose growth forms dominate; however, 

foliose lichens such as Parmotrema praesorediosum (plate 12B), Physcia erumpens

(plate 20E), and Physcia sorediosa (plate 17B), as well as squamulose species in 

the genus Phyllopsora can be found occasionally. Species of filamentous lichens 

such as Coenogonium linkii (plate 2G) can be frequently found on the base of tree 

trunks. Dichosporidium nigrocinctum (plate 3, C and D), Herpothallon aurantiacoflavum (plates 2H and 3A), and H. minimum (plate 21E) are examples of byssoid 

growth forms found sporadically in these forests. 

Species that are commonly observed in these forests include Diorygma 

poiteai (plate 13, A and B; plate 22E), Graphis glaucescens (plate 13, E and F), 

Hemithecium balbisii (plate 13, C and D), Opegrapha dekeselii (plate 14B), Physcia 

sorediosa (plate 17B), and Porina curtula (plate 21F). Several species have only 

been found in this type of forest, e.g., Arthonia aff. rubella (plate 21G), Coenogonium dimorphicum (plate 21H), Coenogonium portoricense (plate 22A), Crocynia 

gossypina (plate 22B), Fissurina adscribens (plate 22C), Graphis farinulenta (plate 

22, D and E), Herpothallon minimum, Lecanographa lyncea (plate 22F), Malmidea

aff. coralliformis (plate 22G), and Schismatomma rappii (plate 22H). Pterocarpus 

forests have the highest number of Coenogonium species recorded among all 

sampled ecosystems. 
68

GENERAL TECHNICAL REPORT IITF-GTR-46

Only two morphotypes of thelotremoid lichens were found in sampled areas 

representative of Pterocarpus forests. These are the encountered morphotypes and 

their representative species:

Sorediotremoid: Chapsa (sorediate)

Leprocarpoid: Chapsa dissuta

Concluding Remarks

Results from this study suggest that tabonuco and palo colorado forests of El 

Yunque National Forest, as well as lowland moist forests, are the ecosystems 

with the highest lichen diversity in Puerto Rico. Along with these ecosystems, 

other forests on the island, such as the state forests of Maricao, Toro Negro, Tres 

Picachos, and Carite, are expected to harbor the vast majority of lichens. Dry 

forests are also species-rich and make a significant contribution to the island’s 

lichen diversity. The least diverse forests of the island are most likely mangrove 

and elfin woodland forests and those in highly human-disturbed areas, such as 

forests in urban environments.

Some evidence appears to suggest that tabonuco, palo colorado, Pterocarpus, 

and dry forests are areas harboring a high number of lichen species that may be 

endemic. For instance, four species from Pterocarpus and dry forests mentioned in 

this report (Coenogonium aurantiacum, C. borinquense, C. dimorphicum, and C. 

portoricense) appear to be endemic (Mercado-Díaz et al. 2013). Several new species 

from tabonuco, palo colorado, and sierra palm forests have been recently described 

and are potentially endemic taxa (Mercado-Díaz et al., in press).

Table 4 summarizes the number of species, genera, and families of corticolous 

lichens found in sampled areas of each forest type described in this report. In this 

sense, these values should be regarded as relative measures of species richness; they 

do not represent the total number of species found in these ecosystems. Although 

limitations related to our sampling approach and other external factors may have 

influenced the robustness of our estimates, we still consider this information valuable because it presents a rough idea of the diversity to be found in these forests. 

An example of how limitations related to sampling may have limited our estimates 

comes from the mangrove ecosystem. Namely, one of the mangrove forest plots was 

considerably higher in species richness than the two other mangrove forest plots 

sampled. It is thought that this higher-than-expected richness is associated with its 

proximity to an adjacent Pterocarpus forest fragment. If this plot were excluded, 

mangrove forests would total 17 species, 9 genera, and 7 families, less than half 

of the richness reported for all taxonomic levels presented for mangrove forests in 

table 4.
69

Lichens in Puerto Rico: An Ecosystem Approach

Acknowledgments

We thank Constance Carpenter and the International Institute of Tropical Forestry 

(IITF) State and Private Forestry (S&PF) Program for their unconditional support 

during the course of this project. Dr. Eugenio Santiago-Valentín, Professor of the 

University of Puerto Rico (UPR) in Río Piedras and Director of the Herbarium of 

the Botanical Garden (UPR), has supported Joel A. Mercado-Díaz’s work and has 

provided resources and space for lichen specimens in the herbarium. Special thanks 

to María Rivera, IITF biological science technician, and to Johanna Colón-López, 

Carlos Castro, Benjamín Curet, Fernando “Madera” Ortiz, and Waldemar Alcobas 

for their company on field trips during completion of this project. Jorge DíazMéndez provided assistance in graphic arts. We are grateful to Christian TorresSantana, Dr. André Aptroot, and Dr. Paul Bayman for their useful comments to 

the report.

Funds sponsoring this report came from the IITF project “Characterizing lichen 

communities along an elevational gradient in Puerto Rico: assessing their role as 

indicators of forest health, biodiversity and microclimate,” led by Joel A. MercadoDíaz, William Gould, and the IITF S&PF and Forest Health Protection programs. 

This work was done in collaboration with the University of Puerto Rico.

English Equivalents

When you have: Multiply by: To get:

Millimeters (mm) 0.0394 Inches

Meters (m) 3.28 Feet

Kilometers (km) 621 Miles

Hectares (ha) 2.47 Acres

Square kilometers (km2) .386 Square miles

Degrees Celsius (°C) 1.8 °C + 32 Degrees Fahrenheit

Table 4—Number of species, genera, and families of corticolous lichens occurring in sampled areas of 

each forest type described in this study

Elfin Palo Sierra Lowland

woodland colorado palm Tabonuco Dry moist Mangrove Pterocarpus

Species 33 85 24 76 77 86 48 59

Genera 17 30 15 32 30 37 27 27

Families 8 15 10 14 17 17 18 14
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GENERAL TECHNICAL REPORT IITF-GTR-46

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Glossary

Apothecia—Disk or cup-like ascoma of Ascomycota.

Ascocarp—An anatomically differentiated structure of asci (sac-like, sporebearing structure) and interascal hyphae enclosed within distinct layers of hyphae.

Ascomata—Fruiting bodies of Ascomycota.

Basidiolichen—Lichenized members of the Basidiomycota.

Basidiomata—Fruiting bodies of Basidiomycota.

Bioindicator—Species that can be used to monitor the health of an environment or 

ecosystem.

Byssoid—Entirely composed of delicate, densely interwoven threads.

Cilia—Long-acute, multicellular hair-like outgrowths with the appearance of an 

“eye lash,” generally originating from the margin or upper surface (but close to the 

margin) of a thallus lobe or along the margin of apothecia.

Columella—A sterile central axis within a mature ascocarp.

Corticolous—Inhabiting the bark of trees or shrubs.

Cyphellae—Pores recessed into the lower thallus surface, surrounded by a pale 

ring and lined throughout with loosely interwoven, non-gelatinized hyphae, originating from the medulla.

Crustose—General growth form where the entire thallus forms a crust.

Dimorphic—Having two growth forms.

Endolichenic—Living in close association with algal and fungal components inside 

a lichen thalli.

Epiphytes—A plant or plant-like organism growing on another plant

Epiphytic—Growing on plants or plant like organisms, as an epiphyte.

Exciple—An anatomical term generally referring to any lateral layer surrounding, 

embracing or enveloping an ascocarp.

Filamentous—Hair- or thread-like.
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Foliicolous—Growing on the surface of leaves of vascular plants

Foliose—General growth form of a “leaf-like” thallus.

Fruticose—General growth form where the thallus is three-dimensional, either 

erect, pendulous (= pendent) or prostrate.

Gelatinous—Jelly-like, gel-like, with a consistency of a gel.

Isidia—A small (mostly 0.5 to 1 mm) asexual outgrowth of the thallus containing 

both mycobiont and photobiont. Often with a granular, warty, pin- or finger-shaped 

appearance.

Lichenization—Any complex organism composed of a fungus in symbiotic union 

with an alga. 

Lobule (pl. Lobules)—A small (possibly juvenile) lobe; flattened and usually 

corticate on both the upper and lower side.

Morphotype—An informal group of taxa with similar or identical morphology.

Parasitism—A close association of organisms that is detrimental for one of the 

symbionts.

Pendulous—Type of fruticose growth which is much stouter, not as finely divided, 

and with vine-like branching pattern.

Photosymbiodeme—A lichen fungus forming morphologically and anatomically 

identical (isomorphic) or different (heteromorphic) thalli with different photobionts.

Pyrenocarp—A globose to flask-shaped ascocarp opening with a pore.

Pyrenocarpous—With a structure and appearance similar to a pyrenocarp.

Rhizines—Root-like strands of closely agglutinated hyphae on the lower side of 

a foliose thallus, usually thread-like to intricately branched, scant to more or less 

numerous; attaching a foliose thallus to its substrate.

Soredia (pl. Soralia)—Microscopic groups of photobiont cells aggregated by 

loosely interwoven hyphae, erupting from cracks or pores in the thallus surface 

with a finely powdery to coarsely granular appearance.

Schizidium (pl. Schizidia)—A scaly propagule, formed by flaking off from the 

thallus surface.

Squamule—A small, more or less complanate, scale-like thallus or thallus segment.

Squamulose—Forming squamules, referring to a growth form intermediate 

between crustose and foliose thalli.

Symbiosis—Any form of cohabitation where two organisms form a close association, thus living together either to the benefit (mutualism) or detriment of one 

another (parasitism) or without any apparent effect (commensalism).

Thallus (pl. Thalli)—The vegetative and assimilative body of both myco- and 

photobiont.

Thelotremoid—Typically referring to a fruit wart commonly observed in species 

of thelotremoid Graphidaceae where the thalline exciple and proper exciple are not 

adherent.