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    Trees of Panama and Costa Rica
    Trees of Panama and Costa Rica
    Trees of Panama and Costa Rica
    Ebook902 pages6 hours

    Trees of Panama and Costa Rica

    By Richard Condit, Rolando A. Pérez and Nefertaris Daguerre

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    About this ebook

    This is the first field guide dedicated to the diverse tree species of Panama and Costa Rica. Featuring close to 500 tropical tree species, Trees of Panama and Costa Rica includes superb color photos, abundant color distribution maps, and concise descriptions of key characteristics, making this guide readily accessible to botanists, biologists, and casual nature lovers alike.


    The invaluable introductory chapters discuss tree diversity in Central America and the basics of tree identification. Family and species accounts are treated alphabetically and describe family size, number of genera and species, floral characteristics, and relative abundance. Color distribution maps supplement the useful species descriptions, and facing-page photographic plates detail bark, leaf, flower, or fruit of the species featured. Helpful appendices contain a full glossary, a comprehensive guide to leaf forms, and a list of families not covered.


    • The only tree guide to cover both Panama and Costa Rica together

    • Covers almost 500 species

    • 438 high-resolution color photos

    • 480 color distribution maps and two general maps

    • Concise and jargon-free descriptions of key characteristics for every species

    • Full glossary and guide to leaf forms included

    LanguageEnglish
    PublisherPrinceton University Press
    Release dateNov 8, 2010
    ISBN9781400836178
    Trees of Panama and Costa Rica

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      Trees of Panama and Costa Rica - Richard Condit

      2009

      Part I

      Introduction

      Chapter 1

      Forests of Panama and Costa Rica

      Tree Diversity in the Tropics of Central America

      Southern Central America excels in tree species richness. On a world map, Costa Rica and Panama, along with western Colombia, Ecuador, and Peru, have the highest plant diversity (Barthlott et al. 1996). Understanding why begins with understanding the topographic and climatic diversity of the region. The Andes in South America and the central cordillera of Central America are a long, near-continuous spine of mountains, and the variation in elevation from lowland to mountain peaks creates variation in habitat. From the warm lowlands to the cool and windswept mountain tops, communities differ, whether of trees, birds, or butterflies. Particularly important in Central America is the contrast between the Pacific and Caribbean flanks of the mountains, which we will return to shortly.

      But there is more to high diversity in Central America than a mountain range. Colorado and Switzerland have mountains, but nowhere near the number of tree species. Indeed, all of North America has about 1000 tree species, compared to 2300 in much smaller Panama. We don'don know the total number of tree species in all of South America, but it is somewhere around 20,000. Scientists have debated this contrast in species richness since von Humboldt traveled the Amazon 200 years ago, and there are nearly as many theories as there are theoreticians. One obvious possibility is glaciation: during the past 200,000 years, while North America and Europe were under ice sheets, Central America maintained a moist, warm climate and dense vegetation. There is plenty of evidence that northern regions suffered extinction during the glacial epoch of the past few million years.

      High species richness is one reason botanists find it difficult to learn, describe, and document plant richness of Latin America. There are far fewer botanists, more species, and less money available for environmental concerns than there are in North America. Indeed, there remain immense gaps in our knowledge of trees in Central America. We have carried out inventories for 20 years throughout Panama, yet we are still unable to identify every tree we see. In fact, in more remote areas that are dif-ficult to visit, it is typical for tropical botanists to leave as unidentified 25% of the species encountered. There is nowhere in North America where an experienced botanist would have anywhere near this difficulty.

      Those North American botanists have excellent field guides (e.g., Elias 1980; Petrides 1972). Comparable guides for trees anywhere in the tropics are scarce, though the number has been greatly expanding in the past decade (e.g., Zamora et al. 2000, 2004). Our hope here is to follow this trend and help other biologists expand their knowledge about the tropics. This guide covers 493 tree species, including 438 with color photos, and we offer descriptions of key features for identification and show where they are known in Panama and Costa Rica. We also offer brief notes about the tree species we do not cover, where they are known, and which of the illustrated species they resemble.

      Geography, Climate, and Forest

      Panama and Costa Rica are well inside the tropics, at 8–10°N latitude, where an atmospheric conveyor belt delivers storm systems out of the east—off the Caribbean—during the northern summer. During the winter, from December through April, this belt shifts southward and the region has its annual dry season.

      The mountain axis of Central America is high enough to intercept storms off the Caribbean, and thus the wettest areas of Panama and Costa Rica are on the Caribbean flanks of the mountains. There, annual precipitation is greater than 3000 mm, with many sites getting 4000 or 5000 mm. The Pacific slope of the isthmus is generally drier, getting less than 3000 mm, and as low as 1500 or even 1000 mm at the driest locations. Though generally drier than the Caribbean slope, the Pacific slope is variable and has both wet and dry areas (Figs. 1.1 and 1.2). The central axis of mountains between the Caribbean and Pacific is nearly everywhere wet, often with clouds and fog.

      To the tree species of Central America, the variation in rainfall is crucial. On the wettest Caribbean slopes, there is enough moisture even during the December–April dry season to keep the soil damp, and forests are wet and green all year. In contrast, much of the Pacific slope has hard, dry soil by April, and many species are deciduous then. By sitting on the cusp of this gradient from dry forest to wet forest, Panama and Costa Rica capture a great diversity of tree species, because the ability to tolerate a dry season is a crucial adaptation.

      In the 1950s and 1960s, a pioneering ecologist named Leslie Holdridge worked for years in Costa Rica and Panama (Holdridge 1967). Holdridge noticed how the variable climate of the region has a conspicuous impact on the forests and developed a system for classifying vegetation to describe it. The Holdridge system has been widely used by tropical ecologists since, especially in Central America. There are a total of 17 categories in the Holdridge system, but a good basic understanding of forest communities in Central America can be gained by abstracting five broad units: dry, moist, wet, lower montane, and upper montane.

      (1) Dry forest. In Panama and Costa Rica, dry forest is found in two regions where rainfall is less than 1500 mm annually, one in central Panama west of Panama City, the other in northwestern Costa Rica (Fig. 1.1). True dry forest in the tropics is short, seldom more than 20 m tall, and many trees lose their leaves during the dry season, quite different from the classic image of tropical rainforest. Fine-leaved trees of the legume family are common. In the driest areas of Central America, there are even columnar cacti and the mesquite tree (Prosopis jubata), both common sights in North American deserts. But it is not a desert in Panama and Costa Rica: trees would occupy the entire region, given the chance. We will return to human impacts later.

      (2) Wet forest. The lowland forests of the Caribbean slope are wet forests of the Holdridge system. Here, the classic image of rainforest holds: trees are tall, the canopy is dense and continuous except for small gaps created by fallen trees, and epiphytes are conspicuous. Trees do not shed their leaves during the weak dry season. Much less conspicuous is what you can decipher only after learning tree species: wet forests have many more species than do dry forests. There are substantial blocks of wet forest throughout Central America, including extensive and unbroken stretches in San Blas, much of western Panama, and the national parks of Costa Rica'Rica Caribbean slope as well as the Osa Peninsula (Fig. 1.1).

      (3) Moist forest. For the forests between wet and dry, we use Holdridge'Holdridge phrase moist forest. This grows where more than 1500 but less than 3000 mm of rain falls, but where the dry season is pronounced and lasts 3–4 months. Trees are tall; indeed, the biggest trees in the area are characteristic of moist forest (e.g., the kapok [Ceiba pentandra] and the espavé [Anacardium excelsum]). On the other hand, there are deciduous species during the dry season. All the easy-to-see forest near the Panama Canal is moist forest (Fig. 1.2), as is a large block in Darien National Park in eastern Panama and much of the Pacific slope of Costa Rica (Fig. 1.1).

      The remaining climatic zones in our abbreviated version of Holdridge are montane: forests above 800 m elevation. There is an important division at about 1500 m, so we consider two categories.

      (4) Lower montane forest. From about 800 to 1500 m elevation, forests resemble lowland wet forests, with tall trees and dense canopy, and wet and lower montane zones share many species. Tropical cloud forests fall in this range, and are typical on the tops of lower mountains, where clouds often sit. There are high densities of epiphytes—orchids, bromeliads, ferns, and mosses—in cloud forests.

      (5) Upper montane forest. Above 1500 and especially 2000 m elevation, forests are quite different, and are sometimes classified as temperate, like forests of North America. Indeed, oak (genus Quercus) and alder (Alnus) are conspicuous above 2000 m, along with many other temperate groups familiar in North America and Europe. Among these temperate trees, though, is a high diversity of tropical taxa. Upper montane forests are not giant forests. Trees are generally less than 20 m tall, and on windswept mountain peaks, trees become sparse or even absent.

      Figure 1.1. Place names and forest zones in Panama and Costa Rica. The dry zone is indicated by yellow, the moist zone by light green, and the wet zone by dark green. A light green topographic line demarcates the lower montane zone, at 800 m elevation, and a black line shows the upper montane zone, at 1500 m.

      Figure 1.2. Place names and forest zones in the Panama Canal Area. The dry zone is indicated by yellow, the moist zone by light green, and the wet zone by dark green. The only topographic line is at 800 m elevation and demarcates the lower montane zone (there is no elevation above 1500 m in the canal area).

      The boundaries between these zones are blurred, and the use of 5 (or even 17) categories is arbitrary. The transition between all types is gradual. There is no place one can stand and point to one forest type on the left and another on the right. Three of the five zones we describe are especially blurred: moist, wet, and lower montane. But categorization is how humans learn to understand variation, and this is why the Holdridge system became popular. To aid in understanding the climate zones, Figure 1.3 shows three distribution maps illustrating typical tree species ranges that are linked to forest zones.

      Where forest remains, all five forest zones are rich in tree species by the standards of North America or Europe, though wet forest is richer than dry forest. Crucial to Central American diversity is another kind of diversity—the change in species between climatic divisions. The wet Caribbean slope is very different in tree species from the moist and dry forests of the Pacific half of the isthmus, and montane forests differ from either, though they are much closer to wet forests. Near the Canal in Panama, the wet forests of Santa Rita and the moist forests near Panama City (Fig. 1.2) are only 50 km apart but share almost no tree species. Much of our scientific research has been about this sharp change in tree species composition in central Panama and the rainfall patterns that cause it (Condit et al. 2001, 2002, 2004, 2005; Engelbrecht et al. 2007). In Costa Rica, very different species can be seen within 150 km in Santa Rosa National Park in the northwest to Braulio Carrillo in the northeast, crossing the mountains in between (Fig. 1.2).

      Human Impact

      As we all understand too well, forests are altered and often simply removed by humans, and the categories of Holdridge do not include human impacts. In fact, deforestation is closely linked to climatic zones (Condit et al. 2001). Humans prefer the tropical dry climate to the tropical wet climate, and tropical dry forests have largely been removed in Central America and indeed much of the world. In Panama and Costa Rica, the drier Pacific slope is mostly pasture interspersed with cities and towns, and we don'don really know what mature dry forest would look like, because there is none. In contrast, the mountains and the Caribbean lowlands of Central America still retain much of their forest and have far fewer humans. Tellingly, there is substantial Pacific forest in wet areas, such as the west side of the Azuero Peninsula in Panama and the Osa Peninsula in Costa Rica (Fig. 1.2), as well as on mountains near the Pacific, where the climate is wet due to high elevation.

      Visiting Forests in Panama and Costa Rica

      Both countries have lovely and extensive forests readily accessible via good roads. In Panama, the easiest forests to reach—and the most familiar to us—are moist lowland forests near the Canal, from Panama City to Gamboa and Pipeline Road (Fig. 1.2). Parque Metropolitano near the city has hiking trails, and though the forest has been heavily disturbed, it is rich in tree species. Taller and more attractive forest can be found at Sendero El Charco, just past Summit Gardens, on the main highway toward Gamboa, and there is a short hiking trail there. Both Metropolitano and El Charco are in moist, secondary forest, with many species typical of the Pacific half of the isthmus.

      The paved road ends at Gamboa, which is surrounded by moist secondary forest. Just beyond starts Pipeline Road, a long dirt road through unbroken forest in Soberania National Park. The first half of the road has a recent disturbance history, but beyond the Rio Limbo, the forests are mature and have been little impacted for at least a century. From a tree perspective, Pipeline Road provides a fascinating switch from the Pacific to the Caribbean: the first two kilometers have a Pacific coast element, with Bursera simaruba and Castilla elastica, but the stretch of road up the steep hill after the Rio Limbo has species of Caribbean coast wet forest (e.g., Welfia regia is easy to see). Permission and a fourwheel-drive vehicle are needed to reach the wet-forest area, but it is an excellent area to visit for both flora and fauna.

      Figure 1.3. Sample species distribution maps illustrating major forest types. Lozania pittieri (Lacistemataceae) has a typical wet-forest distribution, mostly on the Caribbean half of the isthmus, but conspicuous at the Osa Peninsula and other Pacific sites where rainfall is higher. It also occurs at some lower montane sites. Caesalpinia coriaria (Fabaceae—Caesalpinioideae) is only found in the two dry zones of central Panama and northwestern Costa Rica. Alnus acuminata (Betulaceae) is confined to the highest mountains in far western Panama through Costa Rica. Red dots are locations from herbarium records or our own inventories, where precise coordinates were noted. All provinces where a species is known are also stippled; because there are records where the province was noted without coordinates, there may be stippling in areas with no dots. Moreover, provinces are political boundaries and not climatic zones, and stippling in a province does not necessarily mean the species occurs throughout the province. Notice that the map of A. acuminata shows stippling along the Caribbean coast in Costa Rica, even though the tree only occurs in the central mountains. This is because boundaries of several provinces straddle the mountains and reach the coast.

      The best example of undisturbed tropical moist forest in Panama is on Barro Colorado Island. It is intermediate between the coasts geographically and also floristically, and species of the Pacific slope (such as the cuipo [Cavanillesia platanifolia]) along with hints of wetter forests (Virola surinamensis as a large example) are common there. Barro Colorado Island also has the biggest trees in Panama, all either kapok (Ceiba pentandra), espavé (Anacardium excelsum), or the sandbox tree (Hura crepitans). The island can be visited with permission from the Smithsonian Tropical Research Institute.

      Excellent Caribbean wet forest also can be visited in a 1-day trip from Panama City, though not as easily as Pipeline Road or forests near the city. A road runs up the Santa Rita Ridge from the Transisthmian Highway, and not far from the highway, near the radio towers, there are small stands of true Caribbean wet forest. Further up the road there are more extensive stands of forest, but it is difficult driving, requiring four-wheel drive and even then not recommendable after wet weather. Similar wet forest can be visited at Nusagandi, about 4 hours east of Panama City, where there are rustic accommodations for tourists. Both Santa Rita and Nusagandi are highly diverse and claim many wet-forest species impossible to see at Barro Colorado Island or Pipeline Road. Another site near the Caribbean that can be reached from Panama City in a few hours is San Lorenzo National Park, at the mouth of the Chagres River. There are accommodations at the former US military base called Fort Sherman.

      Montane forest at 800–1000 m in elevation is also easy to visit near Panama City, at Cerro Campana about 1 hour west of Panama City, and Cerro Azul and Cerro Jefe, which are just north of the Tocumen (Panama City) airport. Cerro Campana has good trails through cloud forest, and there are various trails and cabins around Cerro Jefe. Both sites are much wetter than the nearby lowlands and have some cloud-forest specialists as well as a broad contingent of wet-forest species that otherwise occur only near the Caribbean coast.

      There are several other areas to visit montane forest in Panama: El Valle not far from Cerro Campana, El Cope, and several sites in Chiriqui, including La Amistad International Park. There is a road from the Pan-American Highway over the mountains to Bocas del Toro that crosses through cloud forest near the Fortuna Dam. Further west, the popular sites for visitors are around the towns of Boquete and Cerro Punta, and this is the only area in Panama where forests above 2000 m in elevation can easily be visited. These harbor a temperate-like flora, with oaks, alder, dog-wood, and elm, but also many tropical taxa.

      Unfortunately, nearly all true dry forest in Panama has been cut down. Forested sites near Panama City are drier than the Caribbean coast but are really moist forest. Savanna-like remnants of dry forest can be seen along the Pan-American Highway west of Cerro Campana and at Sarigua National Park near the town of Chitre, but you need to visit Costa Rica to see extensive dry forest.

      Costa Rica has excellent parks spanning the range of climates, indeed, Panama'Panama parks aspire to match Costa Rica'Rica system. Near San Jose, the capital city, Santa Rosa, Guanacaste, and Braulio Carrillo national parks offer easy access and excellent trails. Santa Rosa, in the far northwest, has been allowed to regenerate for 30 years, and is the only spot in either Panama or Costa Rica where true dry forest can be seen. From Santa Rosa eastward over the mountains and down through Braulio Carrillo offers a marvelous transect through all the climate zones.

      In the far south, the Osa Peninsula is peculiar for having a wet-forest climate near the Pacific coast. The extensive forest there is protected in Corcovado National Park, and there are lodges around the park and remote camps and cabins within. Indeed, thanks at least partly to the popularity of ecotourism, visitors can easily reach all manner of forests in Costa Rica and Panama without much difficulty, from remote and undisturbed wildernesses to city parks. Whether by bus, rented automobile, or with tour groups, all forest zones of the two countries can be visited within a day of the major cities. We hope this book will help nature tourists learn something about the trees as excellent guides (Ridgely 1978) do for the birds.

      Chapter 2

      Tree Identification

      Learning Plant Families

      We emphasize the importance of learning the traits of plant families as a step in identifying species. Families are groups of related species that usually share conspicuous and easy-to-learn characteristics. In animals, dogs (wolves, foxes, etc.) are a family and cats (leopards, bobcats, etc.) are another. In both examples, few people have any difficulty recognizing the similarities that link groups of species within the families or any trouble separating dogs from cats. Plant families are likewise readily distinguished, though sometimes not as obviously as dogs and cats. Once you know families well, the list of potential matches for the specimen in your hand is greatly narrowed.

      A second reason to learn plant families is that the number of entities is manageable. We cover 83 plant families in this book, a reasonable number to keep track of. Since learning half the families would make you an expert on Central American flora, you have much to gain from knowing 40-odd groups of plants. Consider it otherwise: there are 2300 tree species in Panama, and to be an expert you should probably know 600 to 800. That is too many entities for most of us to memorize.

      Learning families is emphasized in Gentry'Gentry (1996) A Field Guide to the Families and Genera of Woody Plants of Northwest South America. We used this book extensively in writing our family descriptions and compiling tables of traits, and anyone set on learning tropical trees of the Americas needs to study Gentry'Gentry book. In our family descriptions, we also relied heavily on Flowering Plants of the Neotropics (Smith et al. 2004).

      As a warning to botanists from North America or Europe, though, the families of trees that dominate Costa Rica and Panama are nearly all unfamiliar in northern forests. Apart from palms, a visiting botanist without tropical experience will find nothing recognizable. Maple, beech, hickory, pine, fir, and redwood—very common trees of forests across the United States and Canada—are not found in the tropics at all. Instead, the major tree groups include the mahogany family (Meliaceae), the coffee family (Rubiaceae), the legumes (Fabaceae), and many more that are either completely unknown or very rare in North America and Europe.

      To help learn the families and their traits, Appendix 1 is a brief glossary of terms used here and elsewhere in the book, and Table 2.1 and Appendix 2 offer a tabular summary of families and their characters. We present drawings in the next section, and other plant guides (Johnson and More 2004; Petrides 1972) have excellent drawings as well. Even better, Harris and Harris (1994) have written a great book on plant vocabulary with drawings, and Wikipedia has a thorough Glossary of Botanical Terms.¹

      The Major Leaf Characters

      The starting point in learning plant families and thus identifying tropical tree species is to know the six basic leaf characteristics. In most cases, these characteristics are easy to see. Much as a good bird-watcher first checks for the bill size of an unidentified bird, these are the traits you first check when examining an unknown tree:

      (1) opposite versus alternate leaves;

      (2) simple versus compound leaves;

      (3) toothed or lobed leaf margins;

      (4) latex;

      (5) clustered versus regular spacing of leaves;

      (6) stipules

      Table 2.1 Leaf Characters of 25 Common Tropical Tree Families of Central America

      The first two leaf traits are the most important and have to be learned. These are always the first two characters to check.

      (1) Opposite versus alternate leaves. Opposite means that two leaves arise from the same position on the branch, so a pair of leaves are precisely opposite one another (Fig. 2.1, bottom). Conversely, alternate means that each leaf arises by itself (Fig. 2.1, top). Note that the terminology might lead to confusion. In both diagrams of Figure 2.1, leaves are on opposite sides of the branch. The determining feature is whether two leaves arise from one spot on the branch (opposite) versus singly (alternate).

      In most species, whether leaves are opposite or alternate is unambiguous, but there are questionable cases. One confusing arrangement is called subopposite, where two leaves are nearly but not exactly opposite. Another ambiguity is where leaves are so closely crowded that it is difficult to see whether they are opposite or alternate. Also, there is a third though rare possibility, with more than two leaves arising from a single spot. These are whorled leaves.

      (2) Simple versus compound leaves. Compound means that individual leaves are divided into separate sections called leaflets. Simple leaves are not thus divided. In the example in Figure 2.2, one leaf has five leaflets. To many who have never studied botany, each leaflet would just be called a leaf, so the structure in Figure 2.2 would be a branch with five leaves. With just a little experience, it is nearly always easy to tell simple from compound.

      Figure 2.1. Alternate versus opposite leaves.

      Figure 2.2. A compound leaf with five leaflets.

      There are two tricks. First, the compound leaves on one tree have approximately the same number of leaflets. This means that the units of leaf tissue tend to come in groups of about the same size. But the approximate qualifier is important: a tree might have most leaves divided into five leaflets, but some will have three or seven. Count how many leaflike units there are in several different groups: if the leaves are not compound, then you are counting the number of leaves per branch, and this number may vary a great deal. But if the leaves are compound, you are counting leaflets per leaf, and the number will be consistent, usually varying by less than four.

      The next trick for establishing whether leaves are compound is to check the spot where the petiole, which is the stalk carrying the leaf, emerges from the branch (Fig. 2.2). In compound leaves, this is nearly always swollen relative to the rest of the petiole and is called a pulvinus. If you are looking at a branch with five leaves, there will not be a swelling.

      Once you have determined that leaves are compound, there are a wealth of obvious features that help identify the tree. The first and most obvious is the number of leaflets, which, as we just noted, is fairly consistent within species. Leaves with just two (bifoliate) or three (trifoliate) leaflets are very consistent (Fig. 2.3, bottom), hence the special names for these cases. With more leaflets, the consistency is looser, so that trees with 21 leaflets are likely to also have leaves with as few as 17 up to 25 leaflets, even on the same branch.

      A second obvious trait of compound leaves is leaflet arrangement. Most compound leaves are pinnate, meaning the leaflets are arranged in two rows on opposite sides of the rachis (Fig. 2.2). Pinnate leaves can have either an odd number of leaflets, or an even number (Fig. 2.3), and this is very consistent within species: in any one tree, you will see odd-pinnate leaves or even-pinnate leaves, but not both.² Generally, odd-pinnate leaves have a series of leaflet pairs plus one terminal leaflet, whereas even-pinnate leaves lack the unpaired terminal leaflet (Fig. 2.3).

      Given that leaves are pinnate, another simple character to check for is whether leaflets are opposite or alternate along the rachis. The definition is the same as for alternate and opposite leaves, but applied now to leaflets: two leaflets emerging opposite one another, from the same position on the rachis, are called opposite leaflets, but if leaflets arise singly they are alternate along the rachis. In either situation, the number of leaflets may be even or odd. As a caution, note that the presence of a terminal leaflet is not always obvious when leaflets are alternate (Fig. 2.4).

      Figure 2.3. Various types of compound leaves. In each, the entire structure is a single leaf, that is, there are six leaves shown in this figure. The most common type is on the far left, where odd refers to the number of leaflets.

      Other arrangements are less common. When leaflets radiate from a single point, like spokes of a wheel (Fig. 2.3), the leaves are called palmate because the arrangement resembles a hand.³ Leaves can also be bipinnate, which means that each leaf is divided once into leaflets, and each leaflet divided again into subleaflets. The precise, botanical term for subleaflet is pinnule (Fig. 2.3). Determining whether a leaf is bipinnate requires applying the rules described above—counting leaflets and pinnules and checking for a swollen petiole base—twice. (You may be wondering whether further divisions are possible, and indeed, one of the 493 species we describe is tripinnate.)

      Having determined whether the leaves are simple or compound, you may need to reconsider whether they are opposite or alternate. Study Figure 2.4. Whether leaves are alternate or opposite hinges on the arrangement of the entire leaf: in (a) and (b) in the figure, the leaves are alternate, whereas in (c) and (d), they are opposite. It is thus possible (and not unusual) for leaves to be alternate while leaflets are opposite, and Figure 2.4 shows other possibilities. Throughout the species descriptions we will repeatedly apply the alternate–opposite dichotomy to leaves and separately to leaflets—check the pictures carefully.

      (3) Toothed or lobed leaf margins. This is easy to see and may be noticed before the first two traits listed above. Oaks are famous for lobed leaves, and every Canadian is familiar with the maple leaf'leaf three main lobes. Teeth are finer, like those on elm leaves. Lobes are always conspicuous, but teeth can be sparse or inconspicuous, and sometimes a wavy margin can be mistaken for teeth. Leaf teeth are also less consistent within families than leaf arrangement (alternate–opposite) or leaf division (simple–compound), that is, quite a few families have some species with teeth and some without. This is why this character comes third and not first.

      (4) Latex. Break off a fresh leaf and check the broken end. Most plants lack latex, and no liquid will appear. But in some species, liquid will drip out rapidly, and in others, droplets will appear at the wound but will not drip. In most cases, latex is conspicuous, but there are species that produce small amounts of barely visible (sometimes clear) latex. Generally, all parts of the tree, not just the leaf, exude latex, so if you break a branch or cut deeply into the bark, you will see some. This is why many trees in well-utilized tropical forests have machete slashes—someone was checking for latex to confirm an identification. Another important detail is that latex dries up. If you pluck a leaf in the field but carry it home to study, the latex may no longer be there. It is a character you should note when the leaf is fresh.

      (5) Clustered versus regular spacing of leaves. Clustering may seem a vague feature, but it is surprisingly consistent within plant families and thus very useful. At one extreme, leaves are spaced very regularly along the branch, and at the other, leaves are clustered toward the branch tip. In the former case, all the leaves typically lie in a flat plane; if you remove such a branch, it will rest easily on flat ground. These are called distichous or two-ranked leaves. In contrast, clustered leaves are usually oriented at many angles, and a branch broken free will not rest flat on the ground. Leaf arrangement can be questionable, for instance if leaves are only slightly bunched, and of course the arrangement is obscured when leaves fall off. But leaf arrangement is always a character worth examining.

      Figure 2.4. Leaf and leaflet arrangements in pinnate leaves. a) Odd-pinnate leaves with nine leaflets. Leaves are alternate, leaflets are opposite. b) Even-pinnate leaves with six leaflets. Leaves are alternate, leaflets are alternate. c) Odd-pinnate leaves with nine leaflets. Leaves are opposite, leaflets are opposite. d) Even-pinnate leaves with six leaflets. Leaves are opposite, leaflets are alternate.

      (6) Stipules. These are the subtlest of the six main traits: you know you are a botanist when you study stipules. They are tiny, weak appendages where the petiole meets the branch (Figs. 2.2 and 2.5), and they frequently fall off leaving only an inconspicuous scar. Many families lack stipules altogether, and though tiny, stipules come in a variety of forms that create family-identifying features. Indeed, stipules are valuable traits in some of the most difficult groups to learn. A problem you will have, though, is knowing when the absence of stipules means they fell off or were never there. Always look for stipules first at the outermost ends of branches, where they are most likely to be retained, then check for thin scars at the base of older leaves, where stipules would have once been.

      Figure 2.5. Stipule and stipule scar. At the lower pair of leaves, the stipule has fallen, leaving a scar behind (a line across the branch). These are opposite leaves, but alternate leaves have stipules and scars as well, as do compound leaves (Fig. 2.2).

      If you spend any time at all trying to identify tropical trees, you will get to know these six major traits and their terminology well, and you will be noting each in every species you see. Soon, you will be counting leaflets and breaking off leaves to look for latex in ornamental plants at shopping malls.

      There are, of course, many other traits that help identify tropical trees, including trunk traits (overall size, buttresses, bark, and branch arrangement), leaf traits (venation, color, hairs, size, odor, and petiole length), plus flowers and fruits. You should be wondering why we omitted these other features from our master list, and there are reasons. The six main traits are (usually) strong dichotomies, easy to observe, and they tend to distinguish families well. Most other traits fail in one respect or another: they represent subtle gradations (leaf color or leaf size), or they do not distinguish families (bark or hairs). Many of these other traits will come up in our descriptions of individual species, but they are less useful at the family level.

      What about flowers and fruits? In botanical keys, they usually come first, and indeed, they are usually more characteristic of families and species than the leaves. The unfortunate truth is, however, that during any visit to a forest anywhere in the world, you will find that very few individuals are reproductive. If you rely on flowers or fruits, you will identify almost nothing. We include photos of flowers for most species, but you must focus on leaves, branches, and the trunk if you want to make any progress identifying trees.

      Categorizing Families by Major Leaf Traits

      Table 2.1 summarizes the six major leaf traits for 25 of the most common tropical tree families, not including the palms (Arecaceae), which are easy to recognize without studying traits. The simplest use of the table is to help memorize the six major opposite-leaved families and the seven major compound-leaved families. Species of these families are fairly easy to learn.

      But note the large number of families with simple, alternate leaves. This is the prototypical tropical tree, and telling those families apart requires delving into more subtle traits, such as leaf clustering and stipules. Even experienced botanists struggle with the large number of species with simple, alternate leaves.

      Knowing the 25 major families well is a great start, but the diverse tropics have many more families than these 25, and in Appendix 2 we tabulate the important characters of 117 families, which cover just about every family of tree you will ever encounter in Panama or Costa Rica. In this full list, there are 78 families that include species with alternate, simple leaves. Even considering that 16 of those are very seldom seen (marked scarce in Appendix 2), and 9 of the rest are strictly montane, there are still 53 families you have to consider if you come across simple, alternate leaves in lowland tropical forest (we cover 46 of those in the main text). This allows us to reiterate the importance of recognizing compound and opposite leaves, because the number of families with either or both those traits is much smaller.

      ¹ http://en.wikipedia.org/wiki/glossary_of_botanical _terms.

      ² There are botanical terms, imparipinnate (odd) and paripinnate (even), but these are good examples of unnecessary technical jargon, because odd- and even- are far easier to remember (see Appendix 1).

      ³ The term digitate also is used (see Appendix 1).

      Chapter 3

      Species and

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