There’s a nice biography at Plant Explorers, a worthy read for today. In that article we learn, among many other interesting details of his life, that he adopted the clothing of the Lapps as his field working clothes. He liked them so much that he had his portrait painted while wearing them. In this portrait, he is holding in his right hand his favorite flower, the Twin-flower, Linnaea borealis.

The image is not as well focused as I would like, but the beetle appeared and then disappeared, never to be seen again. So this is what I got.

The other beetles, the weevils that I saw last year and also two weeks ago, returned, as did the bees. This time all insects were in much greater number – probably a thousand bees at this one plant by 7:30 in the morning. I had a harder time estimating the beetles, but there were easily twice the number that there were two weeks ago.

I do not expect this plant to produce more profuse blooms this season. Now is the time to gather all my notes and try to make sense of what went on.

In a much more humble celebration today, I launched another blog, The Accidental Botanist, where I can ramble on about plant things that are unrelated to our neotropical savanna.

From the Preface:

Photosynthesis is central to all aspects of plant biology as the provider of energy and assimilates for growth and reproduction, yet how it is regulated by abiotic stresses, such as salinity and water deficits, and by biotic stresses, such as insect herbivory, is still unclear.

Every article can be read in its entirety for free. (It is the custom for academic journals to require a subscription or at least an online purchase before you can read the entire article. Abstracts are usually shown for free.) Here’s a wonderful opportunity to see the latest thinking about what happens to plants under, say, the stress of drought and salt. Something to get your teeth into.

The orchid stems can grow to 3 meters tall, and the flowers are at the very top, so their gradual leaning over the past week or so gave me the chance to take some images of the lovely flowers.

Panama is home to no doubt hundreds of species of native orchids, and Potrerillos has a particularly fine climate for them, but the first orchid I decide to write about, this one, was introduced from Asia! My excuse is that this orchid is highly conspicuous, being very popular as a cultivated plant. It’s been introduced to Puerto Rico, Costa Rica, Guatemala, and Panama, according to wikipedia, for this purpose. I had to wonder what the chances were that it would become an invasive plant.

If you don’t live in our neighborhood, and you’ve seen these orchids, you may very well know them as “bamboo orchids.” They are reminiscent of bamboo, with their reedy stems, formation of large clumps, and fairly tall size. Their scientific name is Arundina gramnifolia.

• Arundina comes from the Latin arundo, meaning reed,
• and gramnifolia means grass-like leaves (botanary).

So let’s take a closer look at these reedy stems and grass-like leaves.

If you saw this plant without its obviously-orchid flowers, how would you know it was not a bamboo or some other member of the grass family?

• The leaves are long and narrow – like grasses
• The leaves have sheaths that clasp the stem – like grasses

There are, actually, quite a few differences in the leaf structure between the orchid and the grasses if you look closely, but the easiest way to tell this plant is not a grass is by checking its stem.

• Grass stems are hollow.
• This stem is quite solid.

By vegetation alone, then, we can see that it is not a grass. It’s the flowers that tell us it is an orchid.

Arundina flowers

Even though we usually see only one flower at a time at the tip of a tall stem, the flowers occur in clusters, though of not more than 10. You can see the buds for new flowers here.

Arundina flowers, like all orchid flowers, have an outer whorl of 3 sepals and an inner whorl of 3 petals. The petals and sepals generally look so much alike that in the orchid world both sepals and petals are called tepals.

In the images below the flower is face down. The sepals are labeled in the left image and have been removed in the right image. (Click on either image for a larger view.)

When you remove the 3 sepals, you are left with 3 petals, but it looks like 2 petals plus another flower! This is a characteristic orchid structure. The middle petal is called the labellum, or lip, and it is always different from the others and larger than the others. It ends up at the bottom of the flower and provides a platform for orchid pollinators (wikipedia).

The next two images show (at left) the petals turned over so you can see the labellum and (at right) the labellum opened up so you can see the yellow-streaked platform highway for the pollinators. (Click on either image for a larger view.)

Okay, then what is that phallic-shaped space module in the middle of the labellum? Oddly enough, it’s, to oversimplify a bit, the male reproductive part of this orchid – the column that carries the packages of pollen, the pollinia, discussed recently here. Without consulting an expert, I’m certainly not going to try to label the parts of this incredible structure, but I think the pollinia are stored in the little cap-bill of the column pointed to by the arrow.

At least, when I touched that part of the column with my finger-tip, it fell off fairly easily. If the pollinator has followed that yellow streak pathway up toward the column, it wouldn’t take too much effort for that cap-bill to detach from the orchid and attach to the pollinator, in my viewpoint, anyway.

So, what pollinates Arundina, and what does the pollinator get in return?

From a study in Puerto Rico, where Arundina graminifolia has become naturalized, and also from Zuchowski in Costa Rica, I would expect bees to be the pollinators here in Panama. However, at the time I was taking pictures, anyway, I saw only ants, some other tiny unidentified insects, and this lightning-bug type guy.

I wasn’t sure the bug was serious, but pretty soon, I saw this:

There he is, traipsing right up the pollinator highway. And what will he get for his efforts? Well, no nectar, that’s for sure. Arundina is what is known as a “rewardless” orchid. Perhaps in this case, fair is fair, because it’s hard for me to see how those pollinia would find a surface on this insect’s body, anyway.

Is Arundina gramnifolia invasive here?

Getting back to that original, idle question – it turns out that this “rewardless-ness” is one of the reasons this exotic plant from Asia may never become an invasive species here in Central America. Studies in Puerto Rico showed that although Arundina graminifolia had become naturalized there, the infrequency of pollinator visits (no nectar reward, why visit?) meant infrequent fruiting and therefore the orchid spreads in its new environment at a rate similar to native species.

Guilt-free exotic plant gardening!

First, the characteristics listed by Gentry (all illustrations from John’s plant):

- simple, usually alternate leaves

- leaves and stems with stiff hairs

- strongly one-sided coiled inflorescence (flower cluster)

In John’s plant, the inflorescence is coiled when young and then
it straightens out.

- mostly butterfly-pollinated flowers

These four characteristics strongly pointed toward Boraginaceae. To really nail the family, though, we thought we ought to look at the fruits and seeds. Here’s what the seed site has to say about the Boraginaceae:

• the fruit is either four nutlets or a drupe (fleshy with a thin skin, such as a grape, plum or cherry)
• there are four seeds

Here are just a few of John’s fruit and seed images (click on any for a larger version):

No question that these fruits are drupes, and the last image shows the four seeds. (You’ll also notice some discoloration in the last image. John says that these fruits, once cut, discolor very quickly, like apples only even more quickly.)

For those of you who remember Michael’s liana, by the way, his plant seems not to belong to the Borage Family – the leaves are opposite rather than alternate, although the opposite leaf arrangement does rarely occur in the Boraginaceae. I’m hoping that one day he’ll have time to identify it and let us know what he learns.

The Borage Family is an honorable one, with about 2000 species. It includes the famous flower, the Forget-Me-Not, comfrey, and of course, borage, for which the family was named.

So, can we go any further than family with this plant? Maybe.

Seven genera of the family Boraginaceae are known for Panama (Miller, 1988) – three genera of trees or shrubs, and four genera of herbs, lianas, vines, or clambering shrubs.

Of the four genera we’re interested in,

• if the flower petals are white, green, or yellow green,
• and the plants are woody
• while the fruits are fleshy

the plant belongs to the Tournefortia genus (Miller, 1988). With a name like that, and with the coiled inflorescence, at least in the early stages, I was sure the name had something to do with a “strong turning” as in tourniquet! Well, guess what, the genus was named for a person – Joseph Pitton de Tournefort, 18th century French botanist who was professor of botany at the Jardin des Plantes (Dave’s Garden Botanary). Sometimes you just can’t outguess botanical names.

Tournefortia is well distributed throughout Latin America.

Fourteen species of Tournefortia are known for Panama, so it may take some time before we know which species John’s liana belongs to, but it’s pretty satisfying to get this far.

And one of the neatest finds (for me) is this. While searching online for more information about Tournefortia, my eye was caught by a link to Dangling in the Tournefortia I had to follow up, of course, and it turned out to be a well-known book of poetry by Charles Bukowski.

Who can resist a title like that? Maybe read some poetry while nibbling on the fruits. What do you think, John?

Update:

Michael has succeeded in identifying his vine. It’s Petrea volubilis, also known as the sandpaper vine from its rough leaves. (Image from wikimedia commons.)

P. volubilis is in the Verbenaceae or verbena family – not in the Boraginaceae or borage family. Both Michael and John thought there were significant differences in the leaves between John’s liana and Michael’s liana. I had thought it possible that the leaves came from the same family. Shows you how much I know!

I have a vine or tree vine… don’t know, that grows in my home in Las Cumbres, and birds and butterfly love the fruit, can you tell me more about it? John Bennett

What a great challenge!

First I studied the pictures carefully, saw that the leaves were alternate, the vine appeared to be woody, which in botanical terms means it is a liana, and the inflorescence was something I’d never seen before. So I turned to Gentry’s key, and then wrote back with some questions:

Could you tell me whether your plant has tendrils, or is it growing up a tree without attaching itself? Also, are those leaf edges slightly toothed or are they completely smooth? Finally, if you break off a leaf, do you see a milky sap or latex coming out of the leaf stem?

John wrote back with his answers, some more images, and some thoughts on the matter.

Hmmm! It’s definitely a “liana”, woody… no tendrils… it is self supporting or at least, partly self supporting, as you might see in the photo. I say this because apart from its main stem, it has a profusion of intertwined lesser ones that are propped up by a wall fence. This makes me wonder what would happen if the fence was removed. It seems the weight of the whole thing might cause it to collapse.

I believe it’s a species native to our islands. The fruit  is edible (I’m still alive) and has an interesting taste, but if you squeeze it for its juice, it rapidly turns brownish; oxidizes or something. The leaves are slightly serrated and no sap when broken.

The first pictures I sent where shot from my house, where my caretaker chopped the branches off to make way for my pepper victory garden.

Later he sent along some nice pictures of creatures that enjoy his liana:

Look who comes to dine at my liana.

Plus a myriad other feathered dinosaurs like the Manacus vitellinus… It’s a beautiful bird, but very secretive. I took some pictures but not well focused. It is quite abundant behind our house in a ravine; but it does come the liana to feed. The seeds of the fruit are very small, so that I chew them when I eat them.

and so does other winged folk like…

or… and…

With his additional information and with the motive of possibly attracting toucans and more beautiful butterflies to my neck of the wood if I could possibly grow this liana here, never mind tasting a new fruit, I went back to Gentry and, well, my entire botanical bookshelf.

I wrote back to John that I thought the liana might belong to the family – sticking my neck out here – Boraginaceae, the borage or forget-me-not family. I sent a picture of an inflorescence from one example at Tropical Plant Guides, but his plant was definitely not from that genus. However, he did write:

Boraginaceae or boraginaceous seems to be in the right track in many respects. I’ll confess that I had made a query back a while, through a friend of mine, Fernando Pascal, that works in the Smithsonian, and I had an answer from a botanist, but then my hard drive collapsed and the answer was among the files that had not been backed up at that moment, so I lost them… but now I seem to recall it could have been the Boraginaceae but, yes there are some differences…

I have developed a relationship whit this liana, because it came up on its own outside of my computer hideaway at home, where I work now days, to avoid traffic madness and fuel bills, plus I get more work done. Anyway, the liana sits there with all these incredible creatures singing, eating, sipping nectar and such. The liana is also quite prolific, its small plants sprouting around the area, I believe the seeds must go through the intestinal tract of birds and, presto¡

So here’s your puzzle: Have you ever seen this liana? Do you know what it is? Do you have any ideas about it? Stories about it? Leave a comment if you do, or if you have any other thoughts along these lines.

John and I are both curious.

Update: Here are the leaves mentioned by Michael in the comments below. It’s possible he’s found the same liana in Cerro Azul. That would be neat. Left = top side; right = bottom side.

Update 2: John has now taken some single-leaf images for comparison. Again, left = top side; right = bottom side.

Hmm. John’s thoughts are:

Not so sure the leaves are the same… the pattern of the “veins” seem to differ, my liana’s veins are more symmetric and the leaf seem to be wider with less undulations at the edge. But… I am only an aspiring botanist, or nature enthusiast.

Anyone else?

Update 3: Michael sent along some images of the flowers from his liana. He now thinks his plant may be in a different family than John’s liana, and he could be right. What do you think?

You may have been able to answer immediately because you are very familiar with all three kinds of flowers, but what was it about this one that told you what it is? If you didn’t know what it was, don’t worry, the answer will be given later.

Orchids, lilies, and irises each belong to a different family: Orchidaceae (22,000 species), Liliaceae (1600 species), and Iridaceae (1500 species), respectively. Each family is widely distributed throughout the world. (Click on any image to enlarge.)

The flowers are so showy and beautiful that they’ve been thoroughly cultivated, and if you’re at all familiar with flowers, you can probably easily distinguish any of the three cultivated flowers. But what if you happen upon one in the wild?

It happened to our friend and naturalist, Michael. He sent around an image by email asking for guesses about a plant he found growing near his new home. He thought it might be an orchid but wasn’t sure. Our friend Carla responded with the tip that prompted this post (tip used by permission):

Peek straight into the center of the flower and look to see if it has long filament-like stamens holding pollen conspicuously on the tips. If yes, you might have a lily.

An orchid, however, would have a solid column holding two or more solid masses, called pollinia, which stick to pollinators, probably on the upper side of the throat.

What a simple and straightforward tip! So let’s look.

I couldn’t find a good image of a Tiger Lily (to keep the theme of the leopard-spot flower in the original image) that was not copyrighted, but here’s a lily that was blooming in our yard in early June this year. Click to enlarge or click on Hi-res for higher resolution options.

Hi-res

Nice long, filament-like stamens (male reproductive parts) holding pollen conspicuously on the tips (nothing more conspicuous than black pollen against a white petal!)

Now, let’s compare it with a much smaller orchid that bloomed in April of this year and that keeps the leopard-spot theme (no reason to do this, just fun). The image is a bit fuzzy – I can’t remember if the wind was blowing or whether I had a shaky hand that day – but you can tell that the interior of this flower does not resemble a lily in the least.

Hi-res

There’s the solid column holding two solid masses, the pollinia. As you might have guessed from Carla’s tip, the pollinia are carried away en masse from the flower. No dithering around with small pollen grains here.

Okay, so Carla’s tip had to do with orchids and lilies. Why did I bring in irises? Because when I went outside to start seeing for myself what Carla’s tip was all about, I saw the mystery flower at the beginning of the post. It’s an iris, and when I peek inside I see something a little bit in between the orchid and the lily.

Hi-res

The stamens are not long filaments with the pollen conspicuously at the ends. They are thick and the black pollen grains are on the side rather than the end. Notice that there are only 3 stamens, not the several we find in lilies. This is one of the distinguishing characteristics between lilies and irises. It may not be so easy to tell that these pollen grains are not glued together into pollinia, but if you were to take this flower apart, you’d see that there are 3 distinct stamens, not the one column that you see in orchids, and you’d see the individual pollen grains crumble off.

So there you have it. A simple way to tell lilies from orchids and even from irises. In short:

• Lilies have long stamens with conspicuous pollen at the ends.
• Irises have only 3 stamens.
• Orchids have one column supporting two or more packages of pollen called pollinia.

The answer, then, to the question at the beginning of the post is: you can tell that this flower is an iris because it has 3 stamens and no pollinia. And, by the way, Michael’s flower was an orchid.

Other differences, of course, can be found among these three families, but these differences are fun and useful, in my mind.

Update: The iris has a scientific name! It was recognized as Neomarica longifolia by user tem0dium on Flickr. With that head start, you can expect a closer look at it sometime in the future.

A couple of years ago someone in a comment to my post on cecropias asked whether cecropia trees were deciduous or evergreen. I had mentioned that the leaves, being big, could become unsightly when many of them dropped from the tree. The image to the left. is of one such leaf. My response was based on my own temperate-climate viewpoint, supported by some Cecropia references and an entry in wikipedia which states that (in botany and horticulture) deciduous plants “…are those that lose all their leaves for part of the year.” I said that “my” cecropia was an evergreen tree because it never lost all its leaves.

The answer did not satisfy me, though, and the question has been nagging at the back of my brain ever since. What is going on with deciduous trees in the tropics? At first I thought that maybe deciduous trees here lost their leaves in the dry season, which would make sense for water conservation. And indeed I did see some trees without leaves at that time. But other trees would lose their leaves at other times of the year, and some trees would lose some of their leaves, but not all of them, seemingly throughout the year.

Finally, I’ve located a paper that is readable, a classic in tropical biology, and that explains what’s going on with deciduous leaves in the tropics. I’ll be quoting and paraphrasing from it extensively throughout this post. The paper is by D.H. Janzen, written in 1975, and it’s called Ecology of Plants in the Tropics (Studies in Biology). To give you a sense both of his style and of the tropical environment, here’s a quote from the Introduction:

…in the same habitat there are tree species that are totally deciduous during a six-month dry season, species that are completely evergreen, and species that drop their leaves in the rainy season and bear them during the dry season.

In temperate climates, you’ll find a few conifers mixed in, say, an beech-maple forest, but you would consider such a forest deciduous because most of the trees there drop all their leaves every winter. None of the trees would lose all their leaves every summer.

Such information begs the question: why do trees drop their leaves?

Why do trees drop their leaves?

Janzen says that leaf drop may be a response to

• increased shading due to the more leaves growing overhead within the tree’s crown or in other trees’ crowns
• damage by herbivores, wind, or falling debris
• dry weather

Increased shading. If there is a gap in the forest or if the area is disturbed, pioneer species of trees will come in, and for these species here is a premium on rapid vertical growth. In these circumstances,

“…leaves tend to be shed almost as soon as a shadow is cast upon them. If minerals can be thoroughly extracted from leaves before discarding…the cellulose skeleton that is lost means relatively little to the plant in a light-rich habitat.” [Janzen]

Aha! This seems to me the perfect explanation for the Cecropia behavior.

Here’s a leaf about to drop from a young Cecropia – zooming in on it in the adjacent image.

Doesn’t that leaf look like it’s had all its minerals and other goodies extracted?

The petioles (leaf stalks) are quite long in Cecropias. Here’s where this one is attached to the tree. Notice the bud coming in just above where the petiole is about to let go. Also, you can see the triangular scars lower down, where other leaves have already been dropped.

Cecropias growing in a forest emerge above the surrounding forest canopy when mature. At this point rapid vertical growth is no longer important and leaf drop slows down.

Janzen notes that once mature, “…it is probably only the crown margins [that] lose some leaves through shading.”

Damage. Here’s an image from a couple of years ago where a young Cecropia suffered severe herbivore damage to its leaves. At the top of the plant you can see the characteristic Cecropia stipule at the top of the stem and young red leaves emerging around it, but the two leaves that run diagonally across the image are practically transparent from the damage.

In the next images, some of the herbivore-damaged leaves have already dropped off another Cecropia plant (left) although some heavily damaged ones are still attached toward the top. New leaves are also coming in.

Janzen asks the intriguing question “…why [do] plants actively discard old leaves instead of simply allowing them to be eaten off[?]” We know that abscission – the intentional dropping of a leaf – is an active process. Leaves stay attached to dead trees. So the plant is dropping its leaves “on purpose” after herbivore damage. Janzen‘s answer is that it must be that

“…when a leaf is discarded, the plant has the chance to extract all possible nutrients from it.”

Further, he notes, dropping leaves may be a way of escaping from herbivores.

“Otherwise, the herbivore population could easily build up on the new leaves if they were produced at a rate of a few per day over a long time.”

Dry weather. Here’s and example of a tree that loses its leaves in the dry season (left), flowers, and then grows new leaves when the rains start (right).

It’s Tabebuia rosea, called roble or oak locally because of its strong wood. Here’s a zoom in on one of its flowers.

Besides dropping leaves for water conservation, the plant may find an advantage in dropped leaves for pollination – its flowers are much more visible to pollinators when the leaves are absent, or nearly so.

As already noted, not all deciduous trees lose their leaves in the dry season, but the longer the dry season, the higher the proportion of trees that do drop their leaves. However, even here there are variations from habitat to habitat, for a tree living along a river may not lose its leaves while a tree of the same species elsewhere will do so.

Further, there are trees such as the nance (Byrsonima crassifolia) and others that drop old leaves and produce new ones during much of the year. Right now we’re getting pretty seriously into the rainy season this year and several trees have actively dropped leaves on the ground beneath them. If you click to enlarge the images you can see no herbivore damage. From left to right: the leaves of Miconia argentea (called dos caros locally), Miconia rubiginosa, (called canillo locally) and Byrsonima crassifolia (nance).

So, how long can a leaf live?

All this discussion about leaves dropping has to make one wonder just how long it is possible for a single leaf to live. Janzen says the understory is a place where leaves are especially resistant to herbivore and mechanical damage and therefore

“…there is no obvious reason why an understory leaf should not live for many years (as indeed do the 3-7-year-old leaves of ericaceous [heath family plants] evergreen shrubs in the understory of deciduous forests in the south-eastern United States).”

Leaves not living in the understory have shorter life spans – along the order of 7 months [Coley and Aide 1991, cited in Santos 2000], perhaps because they can maintain a high growth rate and therefore have high leaf turnover rates.

What, then, is a deciduous plant?

At this point I had to re-think the definition of a deciduous tree or plant being one that loses all its leaves during a certain period of time. Janzen shows throughout his article that there is a continuum of leaf-drop behavior, especially in the tropics, that depend on habitat, herbivores, and many other conditions. The Cecropias mentioned in several of my reference books are described as “evergreen” yet, as we’ve seen from many examples, they lose leaves often. Some deciduous trees, on the other hand, may drop all their leaves in one day and within two or three days be flush with new leaves!

In the wikipedia discussion of “deciduous,” it is pointed out that intermediate plants may be called semi-deciduous or semi-evergreen. At this point, I’ve begun to think that all the plants in this neotropical savanna are semis!

The first plant grows in very poor soil – even poorer than the average on our abandoned-pastureland/depleted-soil property. We have a few areas that are so rocky and the soil so thin that the only way it can be maintained is by weed-eater. On this particular slope we have let some shrubs survive the weed-eater in the hope that some day the area will develop into a natural site for native trees and shrubs.

Looking from the top of the slope down toward the gully where rainy season rain drains into the quebrada (seasonal spring) we can see several shrubs. I’ve circled a shrub of interest, coming closer to it in the next photo.

This shrub is in fruit now and although I failed to get a photograph when it was in flower last February, I have reason to believe it is a guayaba de sabana (guava of the savanna), Psidium guineense, which is in the Myrtaceae family.

The second plant grows in a relatively richer area. I did manage to get a photograph of one of its flowers, and you can see the white petals and many stamens of a typical myrtle family flower. The area has fewer rocks than the slope and can be easily mowed. At various other places on the property, we have similar shrubs, and all of them seem identical to this second plant. The plant on the slope seems different from the rest in ways that you’ll soon see.

What makes me think it’s a guava?
Almost as soon as I learned to recognize members of the myrtle (Myrtaceae) family, I knew that these plants were in that family. The flower above certainly fit. The vegetative characteristics, you may remember from other posts (on Eugenia and on Myrcia), are quite simple:

• simple, opposite leaves with smooth margins or edges – both plants have them (left=slope; right=meadow)

• punctations (translucent dots) on the leaves – the ones on the slope are harder to see in the images because the tiny hairs obscure the punctations, even after clicking to enlarge, but they’re there – the indentations at the end of the arrows on the meadow leaf are somewhat easier to detect, especially after clicking to enlarge (left=slope; right=meadow)

• thin, peeling bark (usually) – both plants have typical Myrtaceae bark (left=slope; right=meadow)

Determining the genus in this family, however, is not so simple. Gentry, who is so good at pointing out the simplest way to identify a family or genus, groups the various genera in Myrtaceae according to the features of the flower cluster, or inflorescence. Eugenia, for instance, is in a group where the

• inflorescence is a raceme (separate flowers attached by short equal stalks along a central stem)
• OR reduced to single flowers.

Psidium, by contrast, is in a group where the

• inflorescence usually has 3 to 15 or more flowers (with a shape different from a raceme botanically but that I don’t want to get bogged down by)
• OR may be reduced to single flowers on small stalks.

Gentry also points out the the leaves of Psidium have prominent secondary veins (the ones branching off the main vein running down the center of the leaf), a feature you can see on all the leaves in the images above. These features were not enough, though, to be certain of the genus. A Psidium specialist, Leslie R. Landrum, has stated that Psidium “…has long been one of the most difficult genera of American Myrtaceae to define. To do so, he uses a combination of floral and seed characters that I couldn’t possibly obtain in a short period of time.

So I turned to Carrasquilla, who has arranged the plants in his book, Trees and Shrubs of Panama, by family. He has only 5 plants listed in the family Myrtaceae, so it didn’t take long to recognize the genus – the guava genus called Psidium.

The Psidium genus

There are about 100 neotropical species of Psidium. They are all guavas and they are all evergreen trees or shrubs.

The name Psidium comes from the Greek word for pomegranate probably because guavas have lots of seeds, although guava seeds are certainly much smaller than pomegranate seeds, as you can see from the image of the ripe fruit at the beginning of this post and from this scan of the sliced green fruits from here.

Because most of the characteristics that distinguish Psidium from other genera in the Myrtaceae family have to do with fine details that I am not able to illustrate, I’ll jump right to the description of the species that Carrasquilla wrote about: Psidium guineense. The common name here in Panama is guayaba de sabana – the guava of the savanna – but it is also known as the Brazilian guava. The species name, guineense, was assigned by a botanist who believed that it originated from the Guinea Coast of Africa, but it did not. It is native to Latin America. It has been cultivated elsewhere, but you can see from this distribution map that its center is in the Neotropics. By clicking on the image you will see a few yellow dots in western Africa and northeastern Australia but all the rest of them are in Latin America.

Fruits of Warm Climates lists these characteristics, among others, for Psidium guineense:

• grayish leaves, 3.5-14 cm long and 2.5-8 cm wide
• leaves stiff, oblong, elliptic, ovate; scantily hairy on the upperside and coated beneath with rusty hairs
• flowers borne singly or in clusters of 3 in the leaf axils (where leaf meets stem) with 150-200 prominent stamens
• fruit round or pear-shaped from 1 to 2.5 cm

I highlighted the leaf characteristics because they 1) convinced me that the plant on the slope was P. guineense and 2) lead me on a bit of a goose-chase regarding the other plants on the property.

In the image below you can see that the undersides of the leaves (most of the leaves you’re seeing) have a rusty tinge. If you could feel them, you’d find them velvety with those rusty hairs. The leaves in the lower portion of the image are showing their upper sides and they do have that grayish tint to their green.

By contrast, the leaves of the plant in the meadow and of all other similar plants on the property are a greener color and have few hairs. If you were blindfolded and were handed a leaf from each plant, you’d have no trouble distinguishing the slope plant from the meadow plant.

Are there two species here?

For some time I was convinced that we had two guava species on the property. Not a single other plant on the property had the rusty-colored, velvety underside to the leaves that the slope plant has. Further, the leaves on the plant on the slope are smaller but the fruits larger than the leaves and fruits on the plant in the meadow. No other plant like this is on the property is in fruit, but the leaves of all the other plants have sizes like the plant in the meadow. I measured 10 leaves from each plant and got these averages:

slope leaves: 8 cm long x 4 cm wide
meadow leaves: 12 cm long x 7 cm wide

Fruits:

slope fruits: 3 cm long
meadow fruits: 1-2 cm long

I spent some time mulling over the differences, wondering whether they were meaningful, even reading up on the definition of species, which is disconcertingly vague. Then I remembered having read about the apple tree in Pollan’s The Botany of Desire: A Plant’s-Eye View of the World. The cultivated apple originated in the forests around Alma-Ata in Kazakhstan (Alma-Ata means “father of the apple,” says Pollan). A recent visitor to the area saw

“…entire forests of apples, three-hundred-year-old trees fifty feet tall and as big around as oaks, some of them bearing apples as large and red as modern cultivated varieties.”

So I thought, who knows how many species of apple were there in those forests? What’s important is that they were all apples.

And what we have here are guavas.

I did go so far as to track down descriptions of all six species of Psidium listed in the Flora of Panama Checklist, and I had to conclude that these plants are not different species. The main contender for the other species (which I really was rooting for) was Psidium guajava, the common guava. It, too, can have densely pubescent (hairy) undersides to the leaves. However, it has many more secondary veins (12-20 pairs) in its leaves than does P. guineense, which has about 8-10.

That clinched it. It seems to me that the number of veins in the leaves are much more likely to be characteristic of a species than the hairy-ness or the size. I content myself, then, with the guavas on our property, the guava of the savanna, Psidium guineense, while thinking of the apples in Kazakhstan, in all their variety.

Update: The online newspaper Hoy! from the Dominican Republic just published an article with recipes and health benefits of guava, an aspect of the fruit I completely failed to mention.

The method certainly seems straightforward:

Two procedures are used to help nature along: pruning of foliage to free up space for trees and planting the desired tree species.

But different species naturally respond differently to the light and space freed up. The article is about a model developed by a Ph.D. student, Marijke van Kuijk, that would help predict forest regeneration. He put his observations of a tropical forest in Vietnam together and called them the PHOLIAGE model. If you’re interested in regenerating a natural area in your own area, you might want to look at the pdf file – which itself is just a summary, but which goes into more detail than the blog post – describing van Kuijk’s work.