January 24, 2016
One of the pleasures of living in a traditional Maya thatched-roofed hut is that when I've been working at the computer and my eyes are tired, I can look outside between the wall's poles. Lately there's been more to look at because with the advent of the dry season and the days getting longer, the birds are developing spring fever. Now more birds are singing, they're more actively feeding and turning up where they can be seen. For example, one afternoon there was a rustling on the ground just beyond the pole wall where I was working, and you can see what I saw between the poles at http://www.backyardnature.net/n/16/160124dv.jpg.
That's a White-tipped Dove, which we've already profiled, but without such a nice picture. Our White-tipped Dove Page is at http://www.backyardnature.net/yucatan/dove-wt.htm.
TRUNK OF THE ROYAL PALM
This week the Hacienda's usual tranquility was interrupted by the noise of a chainsaw, followed by the ground shaking when a tree fell. The next day I saw that the victim had been one of the Hacienda's many Royal Palms, diseased on one side and threatening to fall. Our page for them is at http://www.backyardnature.net/yucatan/royal-pm.htm.
You can see the sections of our fallen tree's cut-up trunk at http://www.backyardnature.net/n/16/160124tn.jpg.
A closer look at the cut face of one section is shown at http://www.backyardnature.net/n/16/160124tq.jpg.
Here we see two features distinguishing palm trunks from trunks of most trees we're familiar with. First, they're not covered with thick, woody bark; second, there's no evidence of annular growth rings. To understand the reasons behind these differences, we have to resort to taxonomy.
In the old days we spoke of all flowering plants as being either dicots or monocots. Dicots generally have net-veined leaves and when their seeds sprout send up two leaves, the cotyledons, atop the stem. Oaks, rose bushes, and bean vines are typical dicots. Monocot leaves usually but not always have parallel-veined leaves, and when their seeds germinate only one cotyledon emerges from the soil. Grasses, lilies and orchids are monocots. Nowadays it's recognized that a few flowering plants don't fit into these broad classifications, such as certain waterlilies, but the dicot/monocot concept is still useful.
All of our northern, Temperate Zone trees -- unless you regard bamboo as a tree -- are dicots, or else conifers such as pine, spruce and fir, which are not flowering plants to begin with. Our Royal Palm stems are so different from tree stems up north because palms are neither conifers nor dicots. Palms are monocots, along with grasses, lilies and orchids, and those plant groups produce neither bark nor annular rings.
In the North's flowering trees, which are all dicots, the only living part of a trunk is the cambium layer, which forms a very thin, filmy zone of cells just beneath the bark of woody trunks and branches. Outside the cambium layer there's dead bark, while inside there's dead wood. When the tree is growing fast, the cambium layer produces large wood cells, and when it's growing slowly, as during the winter, the cells are small and usually darker. These differences in cell size and shade, produced by seasonal variations in rates of growth, are the tree's rings. In contrast, palm trunks don't have cambium layers. The entire interior of a palm trunk is alive and remains alive during the palm's life, which can be hundreds of years in some species.
Palm trunks have been described as analogous to reinforced concrete pillars, with the conductive tissue, or "vascular bundles," being like steel rods or rebar, and spongy "filler" parenchyma cells analogous to concrete. On our trunk cross-sections, the vascular bundles composed of vesicles that conduct water and dissolved nutrients up the trunk and photosynthesized carbohydrates down the trunk can be clearly seen amid spongy parenchyma, at http://www.backyardnature.net/n/16/160124tl.jpg.
Up closer, the analogy with steel rods and concrete is more obvious, as seen at http://www.backyardnature.net/n/16/160124tm.jpg.
In palms, all new leaves and flowers develop from what's called the trunk's "heart" or "bud," or more technically the "apical meristem." This means that the apical meristem is surrounded by leaf bases -- the attachment points of frond petioles. In most palm species, where the apical meristem or "heart" remains close to the ground, this means that most stem growth of a young palm is outward, not upward. Royal Palms, however, are part of that small group of species whose apical meristems are borne upward by the lengthening trunk. On a Royal Palm, the heart, or zone of apical meristem, is clearly visible as a constriction in the trunk, at which point there's brown trunk below the constriction, and green "crownshaft" above. You can see constrictions and crownshafts atop trunks in our picture at http://www.backyardnature.net/yucatan/royal-pn.jpg.
The crownshaft is composed of petioles of the palm's fronds wrapping around one another, the newest petioles on the inside, the older ones on the outside. Among the trunk sections lying on the ground in our photo, the section bearing the tree's heart or apical meristem, constricted at the end holding the heart, is shown at http://www.backyardnature.net/n/16/160124tp.jpg.
The tree section in that picture's lower, left corner belongs to another tree, a dicot bearing bark.
An important point about palms producing leaves and flowers only at the apical meristem is that if that part is killed and the palm is of the kind producing just one stem, like our Royal Palm, the palm's life is finished.
Another important difference between Northern tree trunks and palm trunks is that when a dicot or conifer tree's trunk is damaged, the wound is compartmentalized and grown over, but stem wounds among the palms are permanent.
Palm roots also are radically different from the roots of dicots and conifers. Palm roots, instead of forming as "their own thing" during the seed's germination, emerge adventitiously from the lower region of the trunk. This region, known as the "root initiation zone," is seen on one of our healthy Royal Palms at http://www.backyardnature.net/n/16/160124to.jpg.
One of our cut trunk sections shows how the trunk's vascular bundles connect with roots forming at the perimeter, at http://www.backyardnature.net/n/16/160124tk.jpg.
If a palm's new roots developing above ground come into contact with dry air, they stop growing. When palm roots emerge from the trunk, they're already thick, but that's as thick as they'll become. Most roots grow outward from the trunk, not down. If a root is cut, branching may occur behind the cut, but the secondary roots will have the same size as the cut primary. Palm roots don't have root hairs. There are also tertiary and fourth-order roots that are somewhat smaller and short-lived than primary roots, and they grow upward toward the soil surface. These are the ones who absorb water and nutrients.
Most of the above information, which enabled me to make sense of what I saw among the cut sections, was gleaned from an excellent Web page by TK Broschat entitled "Palm Morphology and Anatomy," presented by the University of Florida at https://edis.ifas.ufl.edu/ep473.
A mostly knee-high plant, an herb bordering on being a woody bush, or the other way around, is making at appearance along our roadsides nowadays. You can see its pinnately compound leaves at http://www.backyardnature.net/n/16/160124ca.jpg.
Pinnately compound leaves fall into two big groupings: Those with a single leaflet at the end of the midrib, or rachis, so that the leaves consist of an odd number of leaflets, and; those without a leaflet at the midrib's tip, so that there's an even number of leaflets. Leaves in the picture mostly have eight leaves, with no leaflet at the midrib's tip. With pinnate leaves, this is always something to notice.
The plants are producing clusters of legume-type fruits held upright like slender fingers or claws of a hand, as shown at http://www.backyardnature.net/n/16/160124cd.jpg.
A feature worth noting about the legumes is the series of regular, narrow constrictions between the beans, giving the fruits a segmented look. And of course any plant with legume-type fruits and compound leaves such as these just has to be a member of the Bean Family, so already we're that far with identification. A look at a flower further directs us toward a very common Bean Family genus, as shown at http://www.backyardnature.net/n/16/160124cb.jpg.
The blossom is almost symmetrical, but the two lower petals are slightly larger than the others, and the stamens are of different sizes, and directed upward, while the curved style swoops downward, then up. The flower is bilaterally symmetrical in exactly the way of blossoms in the big genus Senna, of which we've already found several species here. The above picture also shows that a good field mark for this species is its abundant hairiness. A side view showing that the calyx below the flower consists of large, scoop-shaped, round-pointed sepals yellow on their margins but greening toward their centers is at http://www.backyardnature.net/n/16/160124cc.jpg.
Since we've seen so many species of the genus Senna, we know that an important field mark for distinguishing the species is whether or not conspicuous glands occur on the leaves' petiole or rachis. This species has them on its rachises, and they are unusual and spectacular, as shown at http://www.backyardnature.net/n/16/160124ce.jpg.
As the leaves age, these glands disappear, maybe eaten by ants or maybe just falling off. One botanical description found refers to the glands as nectaries, indicating that they produce nectar, though to me they look more like they are providing food to ants, who will bite animals nibbling on the plant.
This is SENNA UNIFLORA, a fairly common weed from northern South America all through Central America north to Mexico and the Caribbean, plus it's invading various other tropical countries, particularly India. There's no good English name for it, though in Mexico it has many, maybe the most commonly used being Frijolillo (Little Bean) and Cacahuatillo (Little Peanut). In Spanish, the suffix "-illo" means "little."
I read that the roasted seeds are used as a coffee substitute, and in traditional medicine the hairy leaves are used as poultices for wounds. The roots serve against dropsy.
THE UNNOTICED HEDYOTIS
In the organic garden's Papaya section the gardeners try hard to keep out the weeds, the ground below the Papaya trees for the most part being naked dirt. Therefore, when a small patch of herbage turned up, it called attention to itself, and once noticed, it looked like something new for me. You can see the lilliputian plant at http://www.backyardnature.net/n/16/160124hd.jpg.
Normally I'd not even think of trying to identify such a minuscule plant but then I noticed the flower at about 4 o'clock from the tip of my lower finger in the picture, and with a flower there's always a good chance for an ID. Pushing my camera's macro capabilities to its limit and then latter doing the same with PhotoShop, I got what's shown at http://www.backyardnature.net/n/16/160124he.jpg.
Even in the first picture we saw that the corolla was four-parted, and now we see another field mark just as important: The flower has an inferior ovary. That means that the white corolla, green sepals and sexual parts arise above the ovary, not below it. Most ovaries are superior. On this flower the inferior ovary is apparent because of how the flower part below the green, finger-like sepals is swollen, before attaching to the slender flower stem, or pedicel, farther down. The picture also shows that the plant bears two leaves per stem node -- they're "opposite" -- and that the ground-hugging stem roots at its leaf-producing nodes. The bristly, while hairs scattered atop the leaves' surfaces are worth noting, too. A close-up of the four-parted flower is at http://www.backyardnature.net/n/16/160124hf.jpg.
In that picture the white, hand-like item emerging from the blossom's throat is the style atop which there's a thick, deeply divided stigma, and it looks like there are four stamens, each affixed where the corolla lobs connect at their bases.
When you have an herb with opposite leaves, inferior ovary, and flowers with parts in fours, the best bet is that the plant is a member of the big Madder or Coffee Family, the Rubiaceae. By doing image searches on the genera of that family known to occur in the Yucatan, and which I didn't know, quickly pictures of our little plant were found.
Our plant is HEDYOTIS CALLITRICHOIDES, distributed from Mexico south to Panama and in the Caribbean Antilles. It's so small and generally unnoticed that I can't find a name for it, not in English, Spanish or Maya, so we'll just call it Hedyotis.
In fact, on the Internet there's very little information about it -- just a few listings where it's been identified here and there, without comments. One observation I can make is that at the Hacienda I find it only where plants are watered each day.
Anonymity often is the fate of plants with no commercial value, which aren't agricultural or ecological threats, and are not used medicinally. Still, ecologically we can see our little Hedyotis is a "pioneer species" trying to stabilize naked soil.
One day someone gave Don Paulino a big papaya. He's one of our gardeners so he saved the seeds, planted them in the organic garden, and now we have a nice crop of papayas, as you can see at http://www.backyardnature.net/n/16/160124pp.jpg.
Something interesting about that shot is that some trees are heavily laden with fruit, others bear no fruits at all, and some have one or a few fruits. That's because Papaya flowers occur in one of three sexual forms: male, female, or hermaphrodite. Hermaphrodite flowers bear both male and female parts, and can pollinate themselves, not requiring another papaya plant to grow nearby.
Among Paulino's papayas I find male and hermaphroditic flowers but no strictly male ones. I read that some cultivars don't produce them, so maybe that's why. Male flowers are most easily recognized by the fact that they are produced in large numbers in diffuse, branched flowering head. You can see such flowering head on a male WILD papaya growing near the hut -- on the picture's right side, with the female tree being on the left -- at http://www.backyardnature.net/yucatan/papaya2.jpg.
Female flowers are much larger than hermaphroditic ones, and the thick, branched, yellow-green stigma atop the ovary is easy to see, as shown at http://www.backyardnature.net/n/16/160124pr.jpg.
That flower has just been pollinated, so its petals are turning brown and about to fall off, leaving only the ovary to mature into a papaya fruit. Female flowers at the peak of their receptivity show only the white, urn-shaped corolla with the forked stigma at its mouth. You can see maturing ovaries at different stages of maturity at http://www.backyardnature.net/n/16/160124ps.jpg.
Hermaphroditic flowers are much more numerous and smaller. You see stamens clustered at their throats, while the ovaries and stigmas are hidden within the corola tube, as shown at http://www.backyardnature.net/n/16/160124pq.jpg.
I read that when growing papayas for the market, at least with some cultivars, hermaphrodite plants are preferred for dependable fruit production. However, the sexuality of such flowers can be unstable and subject to “sex reversal.” Cool weather or high soil moisture can lead to a shift toward femaleness, and fruits of such sex-reversed flowers develop deformations are are unmarketable.
Paulino did something interesting to some of his Papaya trees, shown at http://www.backyardnature.net/n/16/160124pt.jpg.
When I asked why stakes had been driven through the trunks he seemed a little embarrassed, and replied that the Maya believe that such treatment causes trees to produce more fruit.
BIRD SPRING FEVER
This week the birds began getting spring fever. Not just the Clay-colored Robins starting their dawn calling, just a little, with their fluty, echoic burblings, and a Mottled Owl whoah, whoah, whoahing next to the hut, but also the Scrub Euphonia with an occasional plaintive syeeu syeeu, the White-fronted Parrots squawking almost too much, and other birds like the Altamira Oriole who have been vocal all along but who now are raising their volume and level of enthusiasm. You can see an Altamira Oriole swinging on maturing dangling fruits of a Spanish Cedar behind my hut at http://www.backyardnature.net/n/16/160124oo.jpg.
Not only do you hear more birds but also see them more, partly because with the dry season many leaves have fallen, opening up the forest, but also because migrants from up North, after skulking quietly in the shadows since arriving, now forage more daringly, often flitting near when snatching a fly or berry.
To the locals this is just what happens as the dry season gets underway, but to us to whom such bird behaviors announce the approach of spring, it evokes all sorts of green, urgent associations.
It's good to feel springy, and to have so many years of spring memories stored up. It's good to see and hear springtime hope and vigor swirling around, and know that it's bound to increase during the next few weeks. Especially I look forward to the Clay-colored Robins calling at their peak, when the polyphony of their continually ebbing and flowing chanting evokes the auditory equivalent of submersion in a coral reef -- an ocean of delicious forms, color and goings-on swirling all around.
I wish you could hear the Laughing Falcon calling from deep in the forest as I write these words, and be as pleased as I am about that emotive message issuing from the forest beneath this precise patch of blue sky, in the center of this big limestone block which is the Yucatan, in this exact spot on little Earth so green and blue with white cloud-swirls as it orbits the Sun so mathematically correct in its random part of our mediocre but gorgeously spinning, sparkling galaxy, in this mysterious Universe in which we humans can't detect, only infer, 96% of reality, the rest being what our greatest minds can only name dark matter and dark energy, all this some kind of Something where illusion and reality are both extremes with a Middle Path, which can't be described, only alluded to, or perhaps experienced without realizing it.
How pretty is the singing of the birds.
Best wishes to all Newsletter readers,
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