JIM CONRAD'S
NATURALIST NEWSLETTER
Issued in Río Lagartos, on the northern coast of
Yucatán, MÉXICO
in Ría Lagartos Biosphere Reserve

May 10, 2015

GULL-BILLED TERNS
Out in the estuary when you see large flocks of birds lounging on sandbars, wading in shallows or floating on the surface, it's always a good idea to scan each bird because you may have a mixed flock with a rare or otherwise interesting species mingling among the regulars. That was the case this week with several small terns foraging atop some Widgeongrass exposed at low tide. Mainly there were Forster's Terns out that day, but something about some of them just didn't seem right. You can see the oddballs at http://www.backyardnature.net/n/15/150510gt.jpg.

Forster's Terns have orangish legs, and the small tern we often see, Sandwich Terns, have yellow-tipped beaks, but these terns have all-black beaks and legs. They're Gull-billed Terns, GELOCHELIDON NILOTICA, which are winter residents on the Yucatan's coasts, but seldom seen here.

Most terns are members of the genus Sterna, and often Gull-billed Terns are assigned to that genus, but nowadays most experts assign them to their own one-species genus, Gelochelidon. That's because Gull-billed Terns are so un-tern-like. For one thing, their beaks are shorter and thicker than other terns'-- like a gull's beak. Also, Gull-billed Terns rarely dive the way other terns do, but rather hawk for insects over marshes as if they were swallows or nighthawks. Their flight also is more gull-like than other terns'.

However, there's not doubt about Gull-billed Terns being terns and not gulls, because their beaks are sharp-pointed, like other terns, and not hooked, like a gull's.

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SPOONBILL GATHERING PLACE
This winter the estuary's Rosette Spoonbills normally showed up alone or in groups of two or three. Lately, however, numerous spoonbills sometimes have been gathering on a small island near the flamingo breeding grounds, as shown at http://www.backyardnature.net/n/15/150510sp.jpg.

You can see a close-up of one part of that island at http://www.backyardnature.net/n/15/150510sq.jpg.

Is this a spoonbill rookery? TheFreeDictionary.Com gives two definitions of a rookery: First, it's a place where large numbers of rooks or certain seabirds or marine animals, such as penguins or seals, nest or breed, and, second; it's a colony of such animals.

These spoonbills are not nesting or breeding on the little island or nearby, and the ephemeral nature of their gathering doesn't strike me as permanent enough for them to constitute a colony, so my guess is that this little gathering of spoonbills is just that, a spontaneous gathering, and nothing else.

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PORTIA TREE FRUITS
Last November we profiled a prettily flowering tree apparently planted next to Río Lagartos's cemetery, the Portia Tree, whose page is at http://www.backyardnature.net/yucatan/portia.htm.

Since then I've found that Portia Trees, members of the Hibiscus Family and native to the Old World Tropics but invasive in the Americas, also commonly grow wild both as weed trees in Río Lagartos and in disturbed places out in the Biosphere.

Nowadays the Portia Trees are fruiting, as shown at http://www.backyardnature.net/n/15/150510th.jpg.

Though Portia Trees' flowers are very similar to hibiscus blossoms, you can see that the blackish, puckery fruits are weird looking things not at all suggestive of the Hibiscus Family. The fruits are lightweight but so hard that a thumbnail hardly can scratch off a bit of skin, and they can hardly be cracked open with bare hands. It's thought that Portia Tree fruits are adapted for dissemination by floating. Studies show that seeds can germinate after a year of the fruit floating in seawater.

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BLACK MANGROVE FLOWERING
At http://www.backyardnature.net/yucatan/blakmang.htm our Black Mangrove page lacks pictures of the tree's flowers. Nowadays the Black Mangroves are flowering, as you can see at http://www.backyardnature.net/n/15/150510bm.jpg.

Before getting to that picture's flowers, notice the white flakes of salt on the leaf at the picture's right. That's how Black Mangrove rids itself of some of the salt in takes in through its roots -- by expelling it through its leaves. Lick the leaf and it tastes salty.

With regard to the flowers, notice how the blossoms are bunched in clusters at the tips of inflorescence branches that fork in a Y-shaped manner -- "dichotomously," as botanists say when the branches are equal on both sides. You can better see an individual flower's bilateral symmetry at http://www.backyardnature.net/n/15/150510bn.jpg.

The flower is bilaterally symmetrical, not radially, because there's only one way you can cut across the corolla so that mirror images occur on both sides -- and that's vertically. If you'd cut it horizontally, you'd end up with all four of the brown, spoonlike stamens on the corolla's top half and none on the bottom. Eventually the fruit will be asymmetrical, too, and you can see in the picture that the rhinoceros-horn-shaped style atop the ovary is tilted upward, and thus also asymmetrical. Actually, the style is not sharp pointed as it seems in the picture. It's tipped with two stigma lobes that on our flower are held together forming a sharp tip; later the lobes will open up, forming a Y.

With such floral features, traditionally botanists have placed Black Mangrove in the Verbena Family, the Verbenaceae. Some think the genus is so unusual, though, that they assign it to its own Black Mangrove Family, the Avicenniaceae. However, modern genetic analysis finds that it fits best in the Acanthus Family, the Acanthaceae. Nowadays authorities are about as likely to put it in one family as another.

In the picture, the ant on the flower is not incidental. Especially now during the late dry season, many insects have a hard time finding non-salty water. V. Rico-Gray in his 1989 study, "The importance of floral and circum-floral nectar to ants inhabiting dry tropical lowlands," finds that "... during the dry season in coastal Yucatan, ants will rely on the nectar produced on the flowers and other reproductive structures as their main liquid energy source." He further points out that in Black Mangrove flowers ants don't pollinate the blossoms, so the ant in the picture is engaged in "nectar thievery."

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MYRMECOPHILA ORCHID
In the mangroves nowadays here and there clusters of pretty flowers wave in the wind atop slender, six-ft-tall (2m) peduncles arising from clusters of green, succulent plants growing epiphytically on mangrove branches, as shown at http://www.backyardnature.net/n/15/150510mm.jpg.

We've seen this before, deep in the mangroves along the Yucatan Peninsula's Caribbean coast north of Mahahual, so already we know that this is MYRMECOPHILA CHRISTINAE, a giant orchid endemic just to the Yucatan Peninsula and parts of Belize and northern, lowland Guatemala.

Something special about Myrmecophila orchids -- of which three species are listed for the Yucatan Peninsula -- is that normally in Nature ants live symbiotically in them. Myrmecophila orchid leaves arise from atop banana-like "pseudobulbs," which are stems modified for water storage. Ants dig chambers in the pseudobulbs, where they live. You can see this orchid's ridged pseudobulbs below their flat leaves at http://www.backyardnature.net/n/15/150510ms.jpg.

The orchid also provides ants with nectar. In exchange, the ants attack herbivores that disturb the orchids. Also, studies of another species of the genus, Myrmecophila tibicinis, find that ants pack many pseudobulbs with debris that includes dead ants and other dead insects, pieces of plant material, seeds and soil. When this material disintegrates, minerals and other nutrients diffuse from it into the orchid body -- important in such a nutrient-poor environment as tree stems suspended well above the ground. Myrmecophila orchids can survive without ants, though it's rare to find them uninhabited in Nature.

Earlier when we encountered this orchid north of Mahahual, it was hard to get to the plants for a close look. This time better pictures were possible. You can see both flowers and fruits atop their tall peduncle at http://www.backyardnature.net/n/15/150510mo.jpg.

A close-up frontal view of an ant-attended flower is at http://www.backyardnature.net/n/15/150510mq.jpg.

A side view of a fresher flower with is lip full extended to serve as a landing platform for pollinators is at http://www.backyardnature.net/n/15/150510mr.jpg.

Myrmecophila christinae is known to occupy not only mangroves but also coastal dunes and sometimes-flooded areas with trees, as well as scrubby deciduous forest such as the thorn forest south of town. In fact, in the scrubby forest area between the mangroves and savanna/ranchland, the species is surprisingly common.

On one Myrmecophila christinae found in the thorn forest, what appeared to be ant-placed debris adhered to the flower-cluster peduncle all the way from the peduncle's base to the the flower cluster. You can see it at the base at http://www.backyardnature.net/n/15/150510mn.jpg.

A picture of the debris among the flower clusters is shown at http://www.backyardnature.net/n/15/150510mp.jpg.

No mention of such debris on the peduncle's surface can be found in the literature, so maybe someday a researcher will be glad to see these last two pictures.

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BIOLOGICAL CRUST
Here at the end of the dry season most ponds and lagoons that during the winter hosted interesting populations of herons, egrets, ducks, rails and the like, now are dry. After the water disappeared, for weeks a soft, sticky mud remained, but eventually the mud's exposed surface turned grayish and crusty, and cracked into brittle, irregular, leaflike patches that shriveled and curled at their edges, as shown at http://www.backyardnature.net/n/15/150510bc.jpg.

Ecologically, these brittle patches of leafy crust are important, for they are what's known to science as "biological soil crust," or "microbiotic crusts," or sometimes just "biocrust."

In southwestern Texas we looked at biological soil crust covering and protecting vast acreages of arid land. At that time we learned that biological soil crusts are complex communities of interrelating and interdependent species of cyanobacteria, algae, fungi, lichens, mosses, liverworts, and many other kinds of microorganisms.

Here, when our marshs' cyanobacteria, algae, fungi, etc. dry out as the dry season gets underway, they form reproductive structures such as spores. When rains return, the propagules germinate into new organisms, most of which will photosynthesize and be eaten by tiny animals such as copepods, water-fleas and other zooplankton, which will be eaten by larger animals such as aquatic insect larvae and tiny fish, which will be eaten by the larger animals we like to watch.

Therefore, the leafy flakes of biocrust covering our dried-out marshes nowadays represent the base of an ecological pyramid that accomplishes its full expression in our very lively rainy-season marshes.

Though the world's forests often are thought of as serving as the main "carbon sinks" keeping carbon out of the atmosphere and thus diminishing problems with global warming, studies show that in areas where higher plants are scarce, as in our frequently inundated salt-marshes, biocrusts are a major component of carbon dioxide uptake by the whole ecosystem. On a global scale, in 2012, Wolfgang Elbert and others in a work published in Nature Geoscience, calculated that carbon assimilation by non-flowering ground covers contributes around 4.5% of that provided by all land vegetation.

Moreover, across the planet, non-flowering plants, or "cryptogams" such as the algae and cyanobacteria in our marsh biocrust, conduct almost half of the Earth's biological nitrogen fixation -- the conversion of atmospheric nitrogen, unusable to higher plants, into usable forms absolutely necessary for plant growth.

So, these crusty, scab-like patches that look so messy and accidental on the beds of our dried-out marshes deserve recognition and protection. Protection, because in many arid environments livestock, offroad vehicles and fires are destroying vast areas of biocrust.

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WOODSON'S CHAMAEDOREA PALM
During the last week in April I camped in the mountain-top hydrological reserve above and to the north of San Andrés Tuxtla, Veracruz, Mexico. Our page describing that reserve and showing a satellite view of the entire region is at http://www.backyardnature.net/mexnat/tuxtla.htm.

The reserve's cloud forest was particularly rich in species of the palm genus Chamaedorea. Most Chamaedorea palms are so small that often they are grown indoor in pots or small gardens, and are known as parlor palms. Chamaedorea palms bear feather-type, pinnately compound fronds like Coconut Palms, but instead of a few large coconut-type fruits their panicle-type flowering and fruiting heads typically consist of numerous spherical, pea-sized drupes attached to thick, orangish branches (the rachis and rachillae). Fronds of smaller Chamaedorea species often are cut from forest trees and sold as slow-to-wilt greenery used as decoration during weddings and funerals. Over a hundred Chamaedorea palms are recognized, all native to the tropical and subtropical Americas.

In the reserve's forest during my late-April visit the smaller Chamaedorea palms were not flowering or fruiting, but one exceptionally large species was. You can see it standing along a forest trail about 20 feet tall (6m), at http://www.backyardnature.net/n/15/150510ch.jpg.

Notice that its trunk is uncommonly slender for such a tall tree, and that only a single trunk is produced, in contrast to the multiple, bunched trunks of many Chamaedorea species. This tree has produced a large cluster of fruits -- an "infructescence" -- loaded with dozens of tiny drupes, barely visible projecting from the trunk's right side about a meter below the leaves. The infructescence is more visible occupying the lower, right corner of the picture at http://www.backyardnature.net/n/15/150510ci.jpg.

An even closer look at the heavily laden infructescence is at http://www.backyardnature.net/n/15/150510cj.jpg.

This is CHAMAEDOREA WOODSONIANA, occurring in wet mountain forests and cloud forests from southern Mexico and Belize south to Costa Rica, and possibly in Colombia in South America. It doesn't have a decent English name, though Woodson's Chamaedorea probably would do.

In Mexico's Tuxtlas area there's another similar-sized Chamaedorea palm, Chamaedorea tepejilote, the Pacaya, whose immature flowering heads when harvested can be cooked and eaten like boiled corn-on-the-cob. The dish is so favored by some that cultivars have been developed with sweeter tasting heads. Chamaedorea woodsoniana differs from the Pacaya, however, by its infructescences bearing more numerous and smaller fruits than the Pacaya.

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CAFECILLO
During the last week in April when I camped in the mountain-top hydrological reserve above and to the north of San Andrés Tuxtla, Veracruz, Mexico, one of the most conspicuously flowering plants in the cloud forest there was a small tree averaging maybe 15 feet tall (4.5m). Occupying the forest's understory and woods edges, the small tree's branches typically were much entangled with branches of nearby tree neighbors, as shown at http://www.backyardnature.net/n/15/150510pa.jpg.

The eye was drawn to these flowers not only because the fair-sized, brightly yellow blossoms strongly contrasted with the forest's general dark greenness, but also the inflorescence branches -- the rachis and rachillae -- were bright red, as seen at http://www.backyardnature.net/n/15/150510pb.jpg.

The trees' fruits weren't yet ripe, but often green, immature ones hinted at the eventual mature fruit's size and shape, as seen at http://www.backyardnature.net/n/15/150510pc.jpg.

In that picture the top of each fruit bears the remains of the flowers' calyxes. That means that the flowers' ovaries had been "inferior" -- produced below the calyx, unlike the majority of flowers whose ovaries develop above the calyx. When a flowering plant's flowers have inferior ovaries, the identification process is simplified since only a minority of plant families produce them.

In the American Tropics, whenever I see a woody plant bearing flowers with inferior ovaries, immediately I check to see if its leaves arise two per stem node, or opposite one another. If they do, then I see if conspicuous "stipules" are present, stipules being small, leafy appendages at the base of each leaf petiole. If the plant bears opposite leaves and conspicuous stipules, then it's a near certainty that the plant will be a member of the large Coffee or Madder Family, the Rubiaceae. Our cloud-forest tree's leaves were opposite, and at the base of each petiole arose slender, sharp-pointed, green stipules, as seen at http://www.backyardnature.net/n/15/150510pd.jpg.

Our little tree is PALICOUREA PADIFOLIA, found in middle-elevation cloud forests from southern Mexico to Panama. Because it's a small tree with opposite, shiny leaves and it produces clusters of roundish fruits, it's vaguely similar to Coffee shrubs, which belong to the same family, and often is called Cafecillo, meaning "little coffee."

The genus Palicourea, though not present in continental North America, is a big one in the American tropics, embracing about 200 species. Normally Palicourea flowers are pollinated by hummingbirds. Almost one-tenth of all Palicourea species are listed as threatened by the IUCN, even though that agency has only reviewed species occurring in Ecuador. Though our Cafecillo was common in the cloud forest above San Andrés Tuxtla, cloud forests themselves are very much endangered by human activity.

It turns out that Cafecillo, Palicourea padifolia, has been the focus of several studies, largely because its flowers are "distylous." Distylous flowers are those produced by species in which two flower types are recognizable, based on whether they have relatively long or short styles, with the two flower types occurring on separate plants. Styles are the "necks" between a flower's ovaries and their pollen-receiving stigmas. Species with distylous flowers are regarded as evolutionary transition states between species with flowers having both male and female parts, and "monoecious" species, in which male and female flowers occur on different plants. Scientists study species with distylous flowers to figure out the advantages of being monoecious, and to learn how the evolution toward the monoecious state may have occurred.

You might be interested in a 2004 study of Palicourea padifolia conducted by Juan Ornalas and others in a cloud forest above Xalapa, also in Veracruz state, published in the American Journal of Botany and freely available online at http://www.amjbot.org/content/91/7/1061.long.

That study found that pollinators and herbivores can affect plant evolution.

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GENTIAN-LEAVED SPIDERWORT
During our travels we've met with several spiderwort species, members of the genus Tradescantia. Spiderworts belong to the Spiderwort Family, the Commelinaceae, a monocot family on the Phylogenetic Tree of Life found not far from the Lily Family. Spiderworts are herbs with somewhat succulent leaves and parallel veins. Their flowers bear three conspicuous petals colored with hues in the blue to red-purple part of the spectrum, and six stamens.

On my camping trip during the last week in April in the mountain-top hydrological reserve above and to the north of San Andrés Tuxtla, Veracruz, Mexico, I met with an interesting spiderwort I'd never seen. It turned up along a deeply shaded trail through the cloud forest, groping toward a sunbeam entering through a break in the canopy above the trail, as shown in a flash-assisted picture at http://www.backyardnature.net/n/15/150510td.jpg.

This spiderwort species was much "leggier" than most -- lots of stem for the number of leaves. Also the flowers were smaller than usual, with curious, upside-down-V-shaped anthers attached at their middles, as shown in very dim light at http://www.backyardnature.net/n/15/150510te.jpg.

Remarkably, the plant's capsular fruits were wholly enveloped by fleshy, purplish-black calyxes, as shown at http://www.backyardnature.net/n/15/150510tf.jpg.

Where leaves attached to the stems, a fringed, collar-like affair surrounded the stem, shown at http://www.backyardnature.net/n/15/150510tg.jpg.

With such unusual traits, this spiderwort quickly revealed itself as TRADESCANTIA ZANONIA, sometimes known as Gentian-leaved Spiderwort. The species occurs in moist to wet forests from southern Mexico south to Bolivia and Brazil, as well as the Caribbean area.

Not much is known about the species. It's thought that its capsular fruits may never split open to lose their seeds the normal way but that, rather, birds are attracted by the black, shiny calyxes covering the fruits, and eat the fruit and calyx together, later to disseminate the seeds the usual way.

A cultivar sold under the trade name Mexican Flag and listed as Tradescantia zanonia is strongly variegated with white and green stripes, and close-together leaves, looking very unlike like this wild Tradescantia zanonia. You can see pictures of the cultivar at http://davesgarden.com/guides/pf/go/102116/.

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FEATURED ESSAYS FROM THE PAST:

"How I met Sally-D" from the January 19, 2007 Newsletter, at http://www.backyardnature.net/n/p/070119.htm

"Horse Manure & Buck's Truck" from the April 10, 2005 Newsletter, at http://www.backyardnature.net/n/p/050410.htm

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Best wishes to all Newsletter readers,

Jim

All previous Newsletters are archived at http://www.backyardnature.net/n/.