The Pteridophytes of Mexico
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Email: cpm bio. In the present paper, we provide a revised, comprehensive description of the sporophyte and gametophyte of the swamp fern, Blechnum serrulatum Rich. External and internal characters of the sporophyte were analysed, including axes, laminae, pinnae, indusia and spores. Intercellular pectic connections of the parenchyma of the rhizomes are reported for the first time. In stipes, cell walls of the aerenchyma tissue contain filamentous protuberances that are composed primarily of cellulose but contain also fatty substances.
The morphology of the gametophyte, from spore germination to gametangia formation, is discussed.
The taxonomic significance of the characters is considered, especially in regard to the relationship between B. The research of C. Atkinson LR The gametophyte and family relationships. Brownlie G Chromosome numbers in some Pacific Pteridophyta. Carlquist S Leaf anatomy and ontogeny in Argyroxiphium and Wilkesia. Inhibition of spore germination. Part I. Herbaria of the world. The climate, geology, and vegetation of Trinidad, with particular reference to the ecology of ferns. Bulletin of British Museum Natural History.
CSIRO PUBLISHING | Australian Journal of Botany
It is the type locality for dozens of fern species including several taxa that have never been collected elsewhere. Plenty of people know where the llano is, but actually getting there is another story. With some careful planning it should be possible to get there and back in a single day, yet the combination of political tension between adjacent land owners, intentional and unintentional misinformation from locals, and general cartographic mishap have confounded us.
Several years of scanning maps, reading now-digitized accounts of 19th century field trips, and long hikes in the surrounding woods had brought us close to the llano, but the rediscovery of what Hartweg described as a "green swampy space in the midst of the woods," along with its limestone outcrops and unusual ferns, has still eluded us.
If we were to find the llano verde , a long hike from San Miguel Yotao looked to be our last good option. After a long, slow drive from Oaxaca City that finished with a tense ascent of a muddy, cliff-hugging logging road, we arrived in San Miguel Yotao around 7pm. We asked around to see if the comisariado de tierra communales village leader responsible for communal land, selected for a term of typically one or two years was available for us to present ourselves and ask permission to work; we were told to return to the municipal building in an hour.
We got dinner at a house where we had eaten while passing through two years before, and returned to the comisariado's office at the agreed time. As the school brass band worked their way through a wandering, free-for-all practice session in the adjacent room, we sat down with the community leaders and explained why we had come: to explore their forest, document the plant diversity, and make some herbarium collections.
We would send a checklist of species and a guide to the local ferns once our work was completed. After twenty minutes of discussion centered on our qualifications and research objectives, the comisariado and his two colleagues conferred amongst themselves in Zapotec for a few moments and then gave us the bad news: because of a dispute over property boundaries with a neighboring community, we would only be able to collect along the road into town, not in the forest extending beyond their village toward the llano verde.
This was discouraging news — would the llano verde elude us again? Facing the prospect of mediocre roadside collecting and sleeping on a concrete floor it was already 9 pm , we got back in the truck and headed for the neighboring village of Santo Domingo Cacalotepec, which offered cabins for rent and possibly better fern hunting opportunities. We arrived in Cacalotepec twenty minutes later, entering the village through an ancient narrow cobblestone street better suited for the resident burros than for our pickup truck.
With some luck and directions from helpful children, we found our way to the center of town. After some searching, we were able to find someone to bring us to the cabins, which were situated in the forest just above the town. As our hosts prepared the cabin for us, we walked around the clearing to get a preview of what ferns might lie in the surrounding forest: Pleopeltis plebeia , Parablechnum falciforme , Sticherus underwoodianus , and Pteridium aquilinum var.
After that brief survey of our surroundings, we settled in for the night around midnight. We would meet with the comisariado early the next morning. When we arrived in town at am, the comisariado , a pleasant but rather serious-looking man named Vicente Vicente, and his committee were already seated in their office. We exchanged pleasantries, took our seats in front of Vicente's desk, and started quite nearly the same conversation that we had the night before in San Miguel Yotao.
Things seemed to get off to a poor start when Vicente informed us that we would have to wait until the town had its next monthly meeting before our proposed research could be discussed and voted upon. The committee broke off into Zapotec, leaving us to wait in botanical purgatory for a few long minutes. They concluded, and to our surprise, Vicente had changed his mind: not only could we collect ferns on their property--we would be guided on an all-day hike into some of their best forest. For the following four days, we would eat breakfast and dinner with Claudia--she and her playful two-year-old daughter Dani quickly became some of our favorite locals.
Claudia packed us tlayudas, an iconic Oaxacan dish that resembles a tortilla-based flatbread pizza, and we were ready for our day trip with Abdias. Our hike started with a long, steady incline through some of the village's collectively owned coffee plantations before reaching a wet, breezy ridge at about meters elevation. In this cooler zone, ferns flourished: Blechnum appendiculatum , Elaphoglossum petiolatum and Lophosoria quadripinnata were especially abundant on the sides of the trail in this area. On the trunks of trees we spotted three common species of Pleopeltis : P.
In wetter areas, a small Selaginella possibly S. We continued on at a fast pace and decided to hold off on collecting until we returned down the same trail later that afternoon. The trail eventually left the forested ridge and began a steep descent through a thicket of Pteridium arachnioideum and a particularly well-armed Rubus.
We assumed the area was a grown-over field that had been cleared for grazing, but Abdias informed us that it had been forested until a few years ago, when a severe fire had burned everything to the ground. Looking around, we found some holdovers from before the fire, most notably Polypodium puberulum , a giant terrestrial polypod with, as its name suggests, densely short-hairy leaves. Further down the thicketed slope, we entered secondary forest dominated by large oaks and a sparse understory of Hedyosmum mexicanum and various Miconia species.
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Ferns were not abundant here, but we did find some nice drought-tolerant species growing along the trail, including Asplenium monanthes , Mildella fallax , Anemia phyllitidis , and Adiantum alan-smithii , a recently described maidenhair that previously was only known from the neighboring state of Chiapas. More common perhaps is the appearance of a single plant or a few isolated ones in a tiny microhabitat, but such isolated and sporadic specimens are rarely observed. Sexual fusion in pteridophytes occurs on inconspicuous, free-living plants known as gametophytes.
These are often associated with similar-appearing but much more common mosses and liverworts. Most gametophytes are green and surficial surface borne , but some are nongreen and subterranean. Surficial photosynthetic prothalli are generally flat and have clear-cut upper and lower surfaces. The upper surface in Equisetum and Lycopodiella is provided with projecting lobes or flattened processes. The under surface, i.
Subterranean gametophytes tend to be much fleshier, either cylindric or thickly wafer-shaped, and yellowish to brownish.
They are extremely difficult to find in nature. Both surficial and subterranean gametophytes depend on free water through which the sperms must swim to reach the egg and achieve fertilization. The male gametes sperms are provided with special organelles equipped with cilia that propel the gametes by their motion.
The Pteridophytes of Mexico
There may be two cilia per sperm Lycopodiaceae, Selaginellaceae or dozens all other modern pteridophytes. Sperms are produced in specialized cases antheridia that are either sunken in the gametophyte or protrude from it. The antheridia release the sperms through a pore. Release depends on maturity of the sperms and the presence of water.
The female gamete egg is located in a bottlelike organ, the archegonium. Sperms swim to the opening at the top of the neck of the archegonium. The neck provides a passageway to the enlarged base venter , where the egg is located and where fertilization takes place. Both antheridia and archegonia may be present on an individual gametophyte, especially if it is growing singly in a culture dish E.
Klekowski Jr. Thus it is possible to have intragametophytic selfing, the fertilization of an egg by a sperm from the same gametophyte. In nature, however, it is believed that the tendency, at least in ferns and Equisetum , is for gametophytes to pass sequentially through all-archegonial or all-antheridial stages. Female gametophytes release soluble substances antheridiogens that stimulate nearby gametophytes to develop antheridia only.
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This tends to promote cross-fertilization between gametophytes of the same or closely related species. It may help explain the well-known predilection for interspecific hybridization to occur, even in species with subterranean gametophytes W. The embryogeny in a number of pteridophytic groups is still unknown or poorly known; what is known has been summarized mainly by D.
Bierhorst The embryos of many pteridophytes develop their organs early, and it is often possible to distinguish the first leaf, the stem, and the root at a few-celled stage. Young sporophytes differ almost as much among the major groups as do the adult sporophytes. In some families, e. In many ferns, however, the juvenile leaves are often strikingly unlike the mature leaves; the "sporelings" have dichotomously constructed early fronds, the two halves corresponding to the two basal pinnae or vein trusses of the intermediate and mature leaves W.
Spore mother cells, located inside the developing sporangia, are often used to study the chromosomes of pteridophytes. The spectacular work of Irene Manton of the University of Leeds, whose book Problems of Cytology and Evolution in the Pteridophyta aroused pteridologists around the world, led to numerous profound changes in our taxonomic concepts. By making preparations of spore mother cells undergoing meiosis, she was able to determine the diploid number 2 n of chromosomes for individual species and also the base number x of chromosomes for each genus she studied.