Selaginella P.Beauv., nom. cons.,
Descripción
Prostrate and creeping to somewhat ascending or fully erect, slightly to much branched; stems with abundant very small leaves, isophyllous and tightly imbricately arranged spirally in several rows, or more commonly anisophyllous in four rows, two lateral rows of larger spreading leaves and two rows of appressed and ascending median leaves on upper side of stems, also with axillary leaves in axils of branches; rhizophores (roots) either basal or from nodes (branchings), dichotomously branched on touching the ground; leaves orbicular to linear, each with a single vein and a minute ligule, sometimes ending in hair-like tips, entire to ciliatedenticulate, glabrous or rarely hispid on upper leaf surfaces, generally green above, silver beneath; sporangia sessile, generally in 4-sided strobili terminal on branches, the sporophylls 4-ranked and slightly modified from the vegetative leaves, usually monomorphic, rarely dimorphic; spores of two kinds (plants heterosporous); microspores and megaspores in separate sporangia but within the same strobilus; microsporangia each with hundreds of microspores (18–31(–63) µm diam.); megasporangia each with four large megaspores (150–1500 μm diam.); spores tetrahedralglobose, with an equatorial flange, in some species the microspores shed as tetrads.
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Forma de vida
Epipétrica, raramente Epífita, generalmente TerrestreA
Distribución
México (país) Nativo y no endémicoA
Categoría IUCN
No incluidaB
Categoría NOM-059-SEMARNAT-2010
No incluidaC
Discusión taxonómica
Selaginella is a genus of 600–700 species, mostly of tropical regions. Two major groups are recognized: the isophyllous species, which are mostly of dry regions of Mexico and western United States; and the anisophyllous species, which represent by far the largest portion of the genus, these largely of wet tropical forests. Eighty species of Selaginella occur in Mexico.
In the key and descriptions below, the following conventions and terminology are used. Exceptions to these conditions are mentioned when significant. In all species, the root-like structures (rhizophores) are straight aboveground, but fork dichotomously in the soil. The green expanded portion of the leaves is referred to as the lamina, excluding the arista or apiculum at the tip. The midveins of leaves and sporophylls are sometimes prominent or “keeled.” Megaspore and microspore colors were determined from air-dried spores of recent herbarium specimens mostly using Ridgway’s (1912) color standards.
The isophyllous species have their leaves basically all alike (linear to lanceolate), thick, often with marginal cilia and pale aristae. Some isophyllous species have the leaves close to the substrate surface morphologically different from those on the side away from the substrate. In this case, the leaves on the side of the axis away from the surface are called upperside leaves, and those on the side toward the surface are called underside leaves. In this case they are called “dimorphic,” as opposed to anisophyllous. Similarly, some species have slightly or strongly different leaves on underground (rhizomatous) and aerial stems. In this case, the leaves are called rhizomatous stem leaves and aerial stem leaves respectively.
In the anisophyllous species both the lateral and median leaves are oblique at base, somewhat distant in the lower parts of the stems, and imbricate in the distal regions. The lateral leaves are often held at right angles to the stem in the lower parts of the plant, but are more ascending distally. The acroscopic bases are usually more exaggerated and overlapping the underside than the basiscopic bases on the stems. The median leaves are strongly ascending, and the outer side of their bases is more exaggerated (sometimes auriculate). Axillary leaves are located at the points of stem branching and are best seen from the underside. They closely resemble the lateral leaves but are more symmetric.
The leaves often possess distinct, elongate, often white, thickwalled cells, called idioblasts or “false veins,” on one or both surfaces. Leaf margins are often differentiated (green, hyaline, or white), and are usually short- or long-ciliate, or sometimes denticulate.
In one group of anisophyllous species stem swellings (“articulations”) occur at points of branching.
Strobili are most commonly quadrangular, though some are dorsiventral with dorsal rows of sporophylls green and spreading, the ventral ones pale green to hyaline and ascending. Megasporangia and microsporangia vary in their distribution within the strobili; the anisophyllous species often have few to only one megasporangia per strobilus, and this is basal and ventral.
Selaginella, the single genus of the family of the spikemosses (Selaginellaceae), is clearly isolated and monophyletic, in all molecular analyses so far attempted (Korall & Kenrick, 1999; Korall et al., 1999; Therrien et al., 1999). It is the sister group of the quillworts, Isoëtaceae, in all “global” analyses performed on pteridophytes (e.g., Nickrent et al., 2000; Pryer et al., 2001). Selaginella and Isoëtes, both heterosporous, are in turn the sister group of the homosporous lycopods (Lycopodiaceae). These three families are the basalmost extant group of tracheophytes (vascular plants), and are sister to all remaining vascular plants.
Relationships within Selaginella have recently been addressed in preliminary work using the chloroplast rbcL gene (Korall & Kenrick, 1999; Korall et al., 1999). Evidence suggests that the type of Selaginella and a few close allies (subg. Selaginella; this group not represented in Mexico) form the basal element in the
family. The isophyllous (homophyllous) species (subg. Tetragonostachys, in the nomenclature of Jermy, 1986; the genus Bryodesma, according to Soják, 1992) form a monophyletic group. The primary center for the diversity of subg. Tetragonostachys is in Mexico and the southwestern United States. The following 21 species are known from Mexico: S. arizonica, S. arsenei, S. asprella, S. basipilosa, S. bigelovii, S. carnerosana, S. cinerascens, S. eremophila, S. extensa, S. landii, S. macrathera, S. mutica, S. parishii, S. peruviana, S. rupincola, S. sartorii, S. sellowii, S. steyermarkii, S. underwoodii, S. viridissima, and S. wrightii.
From the molecular data published so far, the sister group to subg. Tetragonostachys appears to be a group of so-called “articulate” species (series Articulatae, an unpublished name; for circumscription, see Somers, 1982, and Somers & Moran in Davidse et al., 1995). These species are anisophyllous (two different kinds of leaves) and also well represented in Mexico, with seven species: S. eurynota, S. marginata, S. schizobasis, S. sertata, S. silvestris, S. stellata, and S. tarda. The group is characterized by having articulations or swollen joints just below each bifurcation of the stems. In the living state, the articulations appear as prominent reddish areas; in dried specimens, they often appear blackish, with a distinct abscission line. Other characteristics of the articulate group are that (1) each strobilus has a single large megasporangium at the base; (2) rhizophores are borne on the dorsal side of the stems; (3) megaspores are exceptionally large and strongly cristate-reticulate; and (4) microspores are yellowish to brownish and echinate. The exact relationship of the articulate species to the homophyllous species (subg. Tetragonostachys) and to the species in subg. Stachygynandrum (see below) are still uncertain.
All 52 remaining species of Selaginella in Mexico fall within subg. Stachygyandrum (sensu Jermy (1986), which is the most species-rich clade in the genus. Subgenus Stachygynandrum comprises anisophyllous (heterophyllous) species, characterized by having ascending, relatively short median leaves and spreading, usually longer lateral leaves. Although the natural groups within
Stachygynandrum are not yet clear, the group called Heterostachys (recognized at subgeneric rank by Valdespino, 1995) is delimited by having dimorphic sporophylls. In Mexico, there are 14 species in this group: S. bernoullii, S. finitima, S. flagellata, S. lineolata, S. minima, S. mixteca, S. moritziana, S. popayanensis, S. porphyrospora, S. prolifera, S. simplex, S. stenophylla, S. tenella, and S. Tuberosa. In addition to having the dorsal and ventral sporophylls oriented differently, species of Heterostachys tend to be prostrate, have flagelliform branch tips or sobols (filiform, leafy, horizontal stoloniferous stems from near the bases of main stems) and rather thin leaves. Another probably natural group includes those species that have a rosette habit with fascicled stems, and strongly imbricate and relatively thick-textured leaves. This group includes S. convoluta, S. gypsophila, S. lepidophylla (resurrection plant), S. nothohybrida, S. novoleonensis, S. pilífera, and S. ribae. A related group, also with imbricate leaves but not as strongly rosette-forming, includes S. acutifolia, S. harrisii, S. pallescens, S. polyptera, and S. pulcherrima.
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In the key and descriptions below, the following conventions and terminology are used. Exceptions to these conditions are mentioned when significant. In all species, the root-like structures (rhizophores) are straight aboveground, but fork dichotomously in the soil. The green expanded portion of the leaves is referred to as the lamina, excluding the arista or apiculum at the tip. The midveins of leaves and sporophylls are sometimes prominent or “keeled.” Megaspore and microspore colors were determined from air-dried spores of recent herbarium specimens mostly using Ridgway’s (1912) color standards.
The isophyllous species have their leaves basically all alike (linear to lanceolate), thick, often with marginal cilia and pale aristae. Some isophyllous species have the leaves close to the substrate surface morphologically different from those on the side away from the substrate. In this case, the leaves on the side of the axis away from the surface are called upperside leaves, and those on the side toward the surface are called underside leaves. In this case they are called “dimorphic,” as opposed to anisophyllous. Similarly, some species have slightly or strongly different leaves on underground (rhizomatous) and aerial stems. In this case, the leaves are called rhizomatous stem leaves and aerial stem leaves respectively.
In the anisophyllous species both the lateral and median leaves are oblique at base, somewhat distant in the lower parts of the stems, and imbricate in the distal regions. The lateral leaves are often held at right angles to the stem in the lower parts of the plant, but are more ascending distally. The acroscopic bases are usually more exaggerated and overlapping the underside than the basiscopic bases on the stems. The median leaves are strongly ascending, and the outer side of their bases is more exaggerated (sometimes auriculate). Axillary leaves are located at the points of stem branching and are best seen from the underside. They closely resemble the lateral leaves but are more symmetric.
The leaves often possess distinct, elongate, often white, thickwalled cells, called idioblasts or “false veins,” on one or both surfaces. Leaf margins are often differentiated (green, hyaline, or white), and are usually short- or long-ciliate, or sometimes denticulate.
In one group of anisophyllous species stem swellings (“articulations”) occur at points of branching.
Strobili are most commonly quadrangular, though some are dorsiventral with dorsal rows of sporophylls green and spreading, the ventral ones pale green to hyaline and ascending. Megasporangia and microsporangia vary in their distribution within the strobili; the anisophyllous species often have few to only one megasporangia per strobilus, and this is basal and ventral.
Selaginella, the single genus of the family of the spikemosses (Selaginellaceae), is clearly isolated and monophyletic, in all molecular analyses so far attempted (Korall & Kenrick, 1999; Korall et al., 1999; Therrien et al., 1999). It is the sister group of the quillworts, Isoëtaceae, in all “global” analyses performed on pteridophytes (e.g., Nickrent et al., 2000; Pryer et al., 2001). Selaginella and Isoëtes, both heterosporous, are in turn the sister group of the homosporous lycopods (Lycopodiaceae). These three families are the basalmost extant group of tracheophytes (vascular plants), and are sister to all remaining vascular plants.
Relationships within Selaginella have recently been addressed in preliminary work using the chloroplast rbcL gene (Korall & Kenrick, 1999; Korall et al., 1999). Evidence suggests that the type of Selaginella and a few close allies (subg. Selaginella; this group not represented in Mexico) form the basal element in the
family. The isophyllous (homophyllous) species (subg. Tetragonostachys, in the nomenclature of Jermy, 1986; the genus Bryodesma, according to Soják, 1992) form a monophyletic group. The primary center for the diversity of subg. Tetragonostachys is in Mexico and the southwestern United States. The following 21 species are known from Mexico: S. arizonica, S. arsenei, S. asprella, S. basipilosa, S. bigelovii, S. carnerosana, S. cinerascens, S. eremophila, S. extensa, S. landii, S. macrathera, S. mutica, S. parishii, S. peruviana, S. rupincola, S. sartorii, S. sellowii, S. steyermarkii, S. underwoodii, S. viridissima, and S. wrightii.
From the molecular data published so far, the sister group to subg. Tetragonostachys appears to be a group of so-called “articulate” species (series Articulatae, an unpublished name; for circumscription, see Somers, 1982, and Somers & Moran in Davidse et al., 1995). These species are anisophyllous (two different kinds of leaves) and also well represented in Mexico, with seven species: S. eurynota, S. marginata, S. schizobasis, S. sertata, S. silvestris, S. stellata, and S. tarda. The group is characterized by having articulations or swollen joints just below each bifurcation of the stems. In the living state, the articulations appear as prominent reddish areas; in dried specimens, they often appear blackish, with a distinct abscission line. Other characteristics of the articulate group are that (1) each strobilus has a single large megasporangium at the base; (2) rhizophores are borne on the dorsal side of the stems; (3) megaspores are exceptionally large and strongly cristate-reticulate; and (4) microspores are yellowish to brownish and echinate. The exact relationship of the articulate species to the homophyllous species (subg. Tetragonostachys) and to the species in subg. Stachygynandrum (see below) are still uncertain.
All 52 remaining species of Selaginella in Mexico fall within subg. Stachygyandrum (sensu Jermy (1986), which is the most species-rich clade in the genus. Subgenus Stachygynandrum comprises anisophyllous (heterophyllous) species, characterized by having ascending, relatively short median leaves and spreading, usually longer lateral leaves. Although the natural groups within
Stachygynandrum are not yet clear, the group called Heterostachys (recognized at subgeneric rank by Valdespino, 1995) is delimited by having dimorphic sporophylls. In Mexico, there are 14 species in this group: S. bernoullii, S. finitima, S. flagellata, S. lineolata, S. minima, S. mixteca, S. moritziana, S. popayanensis, S. porphyrospora, S. prolifera, S. simplex, S. stenophylla, S. tenella, and S. Tuberosa. In addition to having the dorsal and ventral sporophylls oriented differently, species of Heterostachys tend to be prostrate, have flagelliform branch tips or sobols (filiform, leafy, horizontal stoloniferous stems from near the bases of main stems) and rather thin leaves. Another probably natural group includes those species that have a rosette habit with fascicled stems, and strongly imbricate and relatively thick-textured leaves. This group includes S. convoluta, S. gypsophila, S. lepidophylla (resurrection plant), S. nothohybrida, S. novoleonensis, S. pilífera, and S. ribae. A related group, also with imbricate leaves but not as strongly rosette-forming, includes S. acutifolia, S. harrisii, S. pallescens, S. polyptera, and S. pulcherrima.
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