Outer Cortical Cells Research Articles

Cells and tissues in the vegetative sporophytes of early land plants.

Remarkable preservation in coalified and pennineralized fossils from Upper Silurian and Lower Devonian sediments deposited some 420 to 390 million years ago provides insight into the major anatomical innovations associated with the early stages in the colonization of the land by higher plants. Using uniformitarian principles, such information, combined with gross morphology, can then be used to reconstruct the pioneers as growing, metabolizing and reproducing organisms, as well as allowing assessment of affinity, although apart from the lycophytes, they have no close relationship with extant groups. In considering vascular tissues, diversity is exemplified by descriptions of the metaxylem in protosteles of Zosterophyllopsida and Drepanophycopsida (putative lycophytes), of Psilophyton (Trimerophytopsida), of the Rhyniaceae (including Rhynia gwynnevaughanii, certain Taeniocrada spp., Sennicaulis) and of Cooksonia pertoni, a Lower Devonian representative of the organization found in the oldest pteridophyte-like land plants. Aglaophyton major is included as a plant with bryophyte-like vascular tissues in a branching sporophyte with cuticle, stomata and intercellular space system typical of the homoiohydric tracheophyte. In all water-conducting cells, interpretation of the primary and secondary wall results from comparisons involving the anatomy and chemistry of extant examples and an understanding of taphonomic processes. Phloem is only rarely preserved and usually identified from its position around the xylem. In contrast, dermal features are better known, because of penetration of the resilient cuticle between epidermal cells. They appear conservative. Thus stomata with two guard cells look remarkably similar to extant forms in surface view, and by consideration of their relationship with surrounding epidermal cells and of extent of cuticularization, seem to have operated in a similar way to those in certain mosses and ferns. Cuticular ornamentation (papillae, striations) and epidermal outgrowths (unicellular and multicellular) are described and their adaptive significance conjectured. Ground tissue systems are best preserved in Rhynie Chert permineralizations where zonation of the cortex is tentatively related to photosynthetic and structural roles. The latter function is also attributed to thick-walled, outer cortical cells recorded in many zosterophylls and in Psilophyton, although the chemical nature of the walls themselves remains equivocal. Problems of identification of roots in plants possessing axial organization with exarch xylem, and in leafy plants with smooth lateral branching systems are briefly addressed. Finally axis apices in Rhynia givynne-vaughanii and sections showing stages in the maturation of Asteroxylon stems are described from the Rhynie Chert. Contents Summary 225 I. Introduction 226 II. Vascular systems 226 III. Dermal systems 237 IV. Ground tissue systems 241 V. Apical meristems 244 VI. Distinction of aerial stems, rhizomes and roots 245 VII. Why anatomy? 245 Acknowledgements 245 References 245.

Morphology and systematics of the red algal parasite Dawsoniocolax bostrychiae (Choreocolacaceae, Rhodophyta)

Abstract The vegetative and reproductive development of the parasitic red alga Dawsoniocolax bostrychiae (Joly et Yamaguishi-Tomita) Joly et Yamaguishi-Tomita, a parasite on Bostrychia, was studied. The thallus is a colourless multiaxial pustule which forms secondary pit connections with cells of its host. Reproductive structures develop from outer cortical cells. Tetrasporangia are tetrahedrally or cruciately cleaved. A four-celled carpogonial branch is borne on an intercalary supporting cell, which also functions as the generative auxiliary cell. After fertilization, the carpogonium fuses with the supporting (auxiliary) cell. The mature carposporophyte consists of a central fusion cell supporting a hemispherical cluster of gonimoblast filaments bearing terminal carposporangia. Carposporophyte development is similar to Harveyella mirabilis (Reinsch) Schmitz et Reinke and Leachiella pacifica Kugrens. Spermatangia develop in globose clusters formed by divisions in several planes of the spermatangial initia...

Morphology and taxonomy of Rhodoglossum gigartinoides (Sonder) comb. nov. (Gigartinaceae, Rhodophyta) from Australia and New Zealand

Abstract The Australasian marine red algal genus Rhodoglossum J. Agardh (Gigartinaceae, Rhodophyta) is distinct from species of Gigartina Stackhouse in the development of the tetrasporangial sorus and in the presence of immersed cystocarps in a foliose thallus. A proposal to reduce Rhodoglossum (and Iridaea Bory) to synonyms of Gigartina is not supported. In the present study, only one species of Rhodoglossum, R. gigartinoides (Sonder) comb. nov., is recognized from southern Australia and New Zealand, this being an earlier name for R. lanceolatum (Harvey) J. Agardh, the type species of the genus. In R. gigartinoides, the tetrasporangia are formed in anticlinal rows by continued apical divisions of outer cortical cells. From these newly formed rows of cortical cells, the inner cells develop into tetrasporocytes, which then enlarge and divide to form cruciately divided tetrasporangia. This mode of development results in the characteristic inwardly radiating series of tetrasporangia and the cortical nature o...

Role of xyloglucan breakdown in epidermal cell walls for auxininduced elongation of azuki bean epicotyl segments

Auxin‐induced elongation of epicotyl segments of azuki bean (Vigna angularis Ohwi et Ohashi cv. Takara) was suppressed by a fucose‐binding lectin from Tetragonolobus purpureas Moench and by polyclonal antibodies raised against xyloglucan heptasaccharide (Xyl3Glc4) when the cuticle present in the outer surface of epicotyls was abraded. In contrast, elongation of non‐abraded segments was not influenced by the lectin or the antibodies. Epicotyl segments, from which the epidermal and the outer cortical cells had been removed, elongated rapidly for 2 h and than only slowly. Auxin slightly stimulated elongation of the inner tissue segments in the phase of slow growth. Neither in the presence nor in the absence of auxin did the lectin or the antibodies affect elongation of the inner tissue segments. The split portions of outer surface‐abraded epicotyl segments incubated in buffer extended outward, and auxininhibited this outward bending. The lectin and the antibodies reversed the effect of auxin on bending. The fucose‐binding lectin pretreated with fucose or the immunoglobulin fraction obtained from preimmune serum exhibited little or no inhibitory effect on auxin‐induced elongation of abraded or split segments. These results support the view that a breakdown of xyloglucans in the epidermal cell walls plays an essential role in auxin‐induced elongation in dicotyledons.

Dudresnaya okiensis sp. nov. (Dumontiaceae, Rhodophyta) from the Sea of Japan

The marine red alga Dudresnaya okiensis sp. nov. (Dumontiaceae, Rhodophyta) is described from the Sea of Japan. It is a deep-water species with the following characters: terete, radially branched thallus, with annulations in young branches, hexagonal crystals in axial cells, hairs, distinct primary axes, cylindrical outer cortical cells, rhizoids up to 36 μm in diameter and bearing cortical laterals, carpogonia once or twice obliquely divided, and an isomorphic alternation of generations; lacking indeterminate-axis primordia, a mucilage coat around the carpogonial and auxiliary-cell filaments, and distinctly cleft cystocarps; and with gonimoblast initials that may or may not be recurved around their auxiliary-cell filament.

Exogenous Ethylene Inhibits Nodulation of Pisum sativum L. cv Sparkle

Exogenous ethylene inhibited nodulation on the primary and lateral roots of pea, Pisum sativum L. cv Sparkle. Ethylene was more inhibitory to nodule formation than to root growth; nodule number was reduced by half with only 0.07 muL/L ethylene applied continually to the roots for 3 weeks. The inhibition was overcome by treating roots with 1 mum Ag(+), an inhibitor of ethylene action. Exogenous ethylene also inhibited nodulation on sweet clover (Melilotus alba) and on pea mutants that are hypernodulating or have ineffective nodules. Exogenous ethylene did not decrease the number of infections per centimeter of lateral pea root, but nearly all of the infections were blocked when the infection thread was in the basal epidermal cell or in the outer cortical cells.

Induction of Pre-Infection Thread Structures in the Leguminous Host Plant by Mitogenic Lipo-Oligosaccharides of Rhizobium

Root nodules of leguminous plants are symbiotic organs in which Rhizobium bacteria fix nitrogen. Their formation requires the induction of a nodule meristem and the formation of a tubular structure, the infection thread, through which the rhizobia reach the nodule primordium. In the Rhizobium host plants pea and vetch, pre-infection thread structures always preceded the formation of infection threads. These structures consisted of cytoplasmic bridges traversing the central vacuole of outer cortical root cells, aligned in radial rows. In vetch, the site of the infection thread was determined by the plant rather than by the invading rhizobia. Like nodule primordia, pre-infection thread structures could be induced in the absence of rhizobia provided that mitogenic lipo-oligosaccharides produced by Rhizobium leguminosarum biovar viciae were added to the plant. In this case, cells in the two outer cortical cell layers containing cytoplasmic bridges may have formed root hairs. A common morphogenetic pathway may be shared in the formation of root hairs and infection threads.

Occurrence of Calcium Oxalate Crystals in Non-mycorrhizal Fine Roots of Picea abies (L.) Karst.

Summary In non-mycorrhizal fine roots of Picea abies grown in hydroponic culture with controlled nutrient supply, apoplastic deposits of calcium oxalate were found microscopically (1) in outer cortical cells between the cell wall and the plasmalemma, and (2) in inner cortical cells within parts of the cell walls adjacent to intercellular spaces. The possible significance of these precipitations is discussed with regard to the transport of calcium, the synthesis of oxalic acid and the necessity to detoxify excess calcium.

Acidic conditions permit effective nodulation of alfalfa by invasion-deficient Rhizobium meliloti exoD mutants.

Rhizobium meliloti exoD mutants are deficient in invasion of alfalfa nodules and, as a consequence, the nodules that exoD strains induce fail to fix nitrogen. These nodules appear to be arrested at the same stage as nodules induced by other exo mutants, which do not make an acidic exopolysaccharide called EPS I, or by ndv mutants, which do not produce a periplasmic cyclic beta(1,2) glucan. However previous genetic and biochemical evidence suggested that the nodule invasion defect of exoD mutants arose from a biochemical deficiency distinct from those of both EPS I-deficient exo mutants and ndv mutants. In this study, we characterize mutant phenotypes of exoD strains in both free-living and symbiotic states. Nodules induced by exoD mutants are generally small and empty of bacteria, and exhibit the same structural features as nodules induced by other invasion-deficient mutants. Putative incipient infection threads were visible in outer cortical cells of these nodules but not in the plant cells in the interior of the nodule. We show that exoD mutants are sensitive to alkaline conditions, ceasing to grow at elevated pH in liquid yeast extract cultures and exhibiting decreased viability in alkaline medium. Interestingly, we find that buffering the plant growth medium at slightly acidic pH (6.0-6.5) restores the ability of exoD mutants to invade alfalfa nodules. exoD mutants are thus alkali sensitive for both free-living and symbiotic phenotypes. This result implies that the nodule invasion defect of exoD mutants arises from their sensitivity to alkaline conditions and, furthermore, that alkaline conditions may obtain in the developing infection thread. The deduced amino acid sequence of ExoD is extremely hydrophobic, suggesting that the protein is membrane associated. We propose models whereby absence of a putative membrane protein might lead to sensitivity to alkaline conditions and consequent arrest of nodule invasion.

Aluminium effects on transmembrane potential in cells of fibrous roots of sugar beet

The effect of aluminium (Al) on the electrical transmembrane potential of epidermal and outer cortical root cells of intact seedlings of sugar beet (Beta vulgaris L. cv. Monohill) was studied. The potential difference to the surrounding medium was recorded with microelectrodes inserted into the vacuoles (PDv) and cytoplasm (PDc) of intact roots. Both long‐term effects of AlCl3 (100, μM present during cultivation) and immediate effects of AlCl3 (10, 50, or 100 μM present in the assay medium), were measured. The effect of Al was measured at pH 4.0, 5.0 and 6.5 in order to obtain information on the toxicity of different Al forms existing at different pH values.Low pH and/or the presence of AlCl3 during cultivation caused large depolarizations of the PDv. Since the immediate effect of 2,4‐dinitrophenol (DNP) on the resting potential of cells from Al‐cultivated plants was negligible, it is likely that Al affects the metabolic component of the transmembrane potential.Aluminium also had an immediate effect on the PD in root cells of plants cultivated without Al. Addition of 10 or 50 μM Al to the assay medium caused hyperpolarization of PDv in the presence of 0.5 mM Ca2+ at all pH values studied, depolarization of PDc at pH 6.5, and hyperpolarization of PDc at lower pH. At 1 mM Ca2+, or in the presence of K+ (≥ 2 mM), however, the same Al concentrations had little effect on PDc.The strongest depolarizing effects of 10 or 50 μM Al in short‐term treatments were obtained at pH 6.5, and were probably due to the soluble species Al(OH)3, which is more frequent at pH 6.5 than at a lower pH. Addition of 50 μM Al caused alkalinization of the root medium at pH 6.5, but not at pH 4.0. Therefore, it is possible that Al at pH 6.5 is bound to, or translocated across, the membrane without the accompanying hydroxide ions. It is likely that most of the Al is bound to the root cells, since removal of Al from the buffer surrounding the roots did not cause the changed PD values to return to the original values. Aluminium also interacts with effects of Ca2+ and K+ on the membrane potential, since changes in PD, induced by changes in concentrations of Ca2+ and K+ are different in the absence and presence of Al.

Life history, morphology and development of a ligulateDesmarestiaspecies from southernmost Chile

The life cycle, morphogenesis and aspects of the fine structure of a ligulate Desmarestia species from the Brunswick Peninsula (southernmost Chile) are described. Unilocular meiosporangia develop, without change of size and shape, from outer cortical cells. Gametophytes are monoecious and become fertile at temperatures ≤ 10°C. Compared to the morphogenesis of sporophytes of other ligulate Desmarestiales, growth of the main axis stops relatively early during development, resulting in the stout appearance of the adult sporophytes. Up to 20 primary laterals have meristems and develop into corticated lateral branches. Secondary laterals with meristems develop into blades. The main axis and the lateral branches become dentate as a result of the cortication of laterals without meristems. Cells of the axial filament are surrounded by many hypha-like cells, and the cross walls of both kinds of cell have numerous plasmodesmata. Physodes occur in every cell type. The characteristics of this species are compared wit...

Histopathology of Wheat Seedling Roots Infected with Pythium arrhenomanes

AbstractTwo‐day‐old wheat seedlings were placed on the edge of a P. arrhenomanes culture for 3 h at 25°C, and transferred into test tubes (18 mm dia.) containing glass beads and 1 ml of sterile water. Roots were sampled every 6 or 12 h for 84 h, and observed with the scanning electron microscope, or serial sectioned for light microscopy. Roots were colonized extensively in the region of root hair formation near the tip within 30 h after inoculation. Extensive penetration occurred 0.1—2 mm behind the root tip, with hyphae breaching the endodermis and gaining entry into the stele. Behind this area, hyphae remained limited to the outer cortical cells, or did not penetrate at all. Hyphae grew intracellularly, and became irregularly inflated inside cells. In most cases, hyphae penetrated the roots directly through the epidermis with appressoria being formed, or through breaks on the surface. However, histological evidence suggested chemical action taking place both outside and inside the cells.

Life history and morphology ofChondrus nipponicus(Gigartinales, Rhodophyta) from Japan

The vegetative and reproductive morphology of Chondrus nipponicus from Japan is described. This species is dichotomously or irregularly branched with marginal and surface proliferations. Plants are dioecious; spermatangia develop singly or in pairs from outer cortical cells; the carpogonial branches are three-celled and borne on a large supporting cell. An enveloping tissue is absent in the mature cystocarp. Tetrasporangia are transformed from intercalary or terminal branches produced secondarily from medullary cells. In culture, tetraspores from plants collected in Oshoro Bay, Hokkaido, and Iwamuro, Niigita Prefecture, gave rise to dioecious male and female gametophytes, but only under short-day conditions at 15°C. In the presence of male plants, female plants formed carposporophytes that released carpospores, which germinated in turn to form tetrasporangial plants under both long- and short-day conditions at 15°C. The species thus has a Polysiphonia-type life history. Gametangial formation is under shor...

DEVELOPMENTAL ANATOMY OF DIRECT SHOOT ORGANOGENESIS FROM LEAF PETIOLES OF VITIS VINIFERA (VITACEAE)

The anatomy of direct shoot organogenesis from leaf petioles of Vitis vinifera cv. French Colombard cultured in vitro was studied by light microscopy. Regenerating petiole stubs were fixed at 2‐ or 3‐day intervals and sectioned longitudinally. By day 3 on regeneration medium, new cell divisions were observed. After 6 days, three distinct regions of meristematic activity were apparent within the expanding petiole stub: the wound‐response, organogenic, and vascularization regions. In the organogenic region, rapid periclinal divisions of vacuolate outer cortical cells formed nodular bumps, many of which developed vascular strands and marginal meristems and formed adventitious leaves. Promeristems with small, densely staining cells and a distinct tunica layer also originated in the organogenic region, by cell division in the epidermal and subepidermal cell layers. With vascularization and the formation of leaf primordia, many promeristems became adventitious shoot meristems. Adventitious leaves and promeristems were initiated continuously from day 10 until day 33. Promeristems were often initiated near or upon adventitious leaves but could form either before or after the adventitious leaf developed. Adventitious leaves and shoot meristems developed vascular connections with the vascular bundles of the original expiant. The implication of this pattern of regeneration for Agrobacterium‐mediated transformation of Vitis is discussed.

Morphological Differences in Vesicular-Arbuscular Mycorrhizae of Gentianaceae Produced by Different Endophytes

Seeds of three species of Gentianaceae were sterile germinated in pot culture and inoculated with three species of Glomus and one Glomus/Acaulospora mix. Mycorrhizae were readily formed. Several differences between normal VA mycorrhizae and those in gentians were observed. In outer cortical cells large loops of hyphae were produced, few intercellular hyphae were present, and spread of the fungal colonization resulted primarily from the external hyphae. Gentian mycorrhizae differed in the size and development of looped hyphae as well as in the sizes and shapes of arbuscules. These differences are probably under the control of the fungus.

DEVELOPMENTAL ANATOMY OF DIRECT SHOOT ORGANOGENESIS IN LEAVES OF VITIS VINIFERA

The developmental anatomy of direct shoot organogenesis from in vitro leaves of Vitis vinifera L. cv. French Colombard was studied by light microscopy. Regenerating petiole stubs of leaf explants were fixed at intervals and were sectioned longitudinally to determine the developmental sequence of direct shoot organogenesis. After 6 days, three distinct regions of meristematic activity were apparent within expanding petiole stub: the wound-response, organogenic, and vascularization regions. In the organogenic region, divisions of vacuolate outer cortical cells formed nodular bumps that sometimes became adventitious leaves. Promeristems, which had the potential to become adventitious shoot meristems, were also initiated asynchronously in the organogenic region. Promeristem initiation occurred by two or several synchronous cell divisions occurring in the epidermal and subepidermal cell layers. Adventitious shoots and leaves developed new vascular bundles that connected to the pre-existing vascular bundles of the explant.

Gravity-Induced Changes in Intracellular Potentials in Elongating Cortical Cells of Mung Bean Roots

Gravity-induced changes in intracellular potentials in primary roots of 2-day-old mung bean (Vigna mungo L. cv. black matpe) seedlings were investigated using glass microelectrodes held by 3-dimensional hydraulic micro-drives. The electrodes were inserted into outer cortical cells within the elongation zone. Intracellular potentials, angle of root orientation with respect to gravity, and position within the root of the impaled cortical cell were measured simultaneously. Gravistimulation caused intracellular potential changes in cortical cells of the elongation zone. When the roots were oriented vertically, the intracellular potentials of the outer cortical cells (2 mm behind the root apex) were approximately - 115 mV. When the roots were placed horizontally cortical cells on the upper side hyperpolarized to - 154 mV within 30 s while cortical cells on the lower side depolarized to about - 62 mV. This electrical asymmetry did not occur in cells of the maturation zone. Because attempts to insert the electrode into cells of the root cap were unsuccessful, these cells were not measured. The hyperpolarization of cortical cells on the upper side was greatly reduced upon application of N,N'-dicyclohexylcarbodiimide (DCCD), an inhibitor of respiratory energy coupling. When stimulated roots were returned to the vertical, the degree of hyperpolarization of cortical cells on the previous upper side decreased within 30 s and approached that of cortical cells in non-stimulated roots. This cycle of hyperpolarization/loss of hyperpolarization was repeatable at least ten times by alternately turning the root from the vertical to the horizontal and back again. The very short (<30 s) lag period of these electrical changes indicates that they may result from stimulus-perception and transduction within the elongation zone rather than from transmission of a signal from the root cap.

Morphology and life history of Predaea kraftiana sp. nov. (Gymnophloeaceae, Rhodophyta) from Australia

Abstract Predaea kraftiana sp. nov. is described from the subtidal in the vicinity of Coffs Harbour in northern New South Wales on the east coast of Australia. Thalli are reniform when young, flabellate and lobed when mature; outer cortical cells are cylindrical, the cortical fascicles being pseudodichotomously branched; vesicular cells are absent; carpogonial branches are generally three cells long, but may be two-, four-or five-celled, with an ampulliform basal cell generally bearing a small, sterile cell similar in morphology to the nutritive cells found on cells in the vicinity of auxiliary cells; fertilized carpogonia divide once transversely, each of the resulting cells forming up to three connecting filaments; gonimoblast initials are produced on the lateral surface of the auxiliary cell opposite the site of connecting filament juncture. In culture, carpospores from field-collected gametophytes developed into crustose plants lacking cell fusions or secondary pit-connections. Irregularly to regularl...

PROPOSAL OF THE GRACILARIALES ORD. NOV. (RHODOPHYTA) BASED ON AN ANALYSIS OF THE REPRODUCTIVE DEVELOPMENT OF GRACILARIA VERRUCOSA1

ABSTRACTThe mode of division of vegetative cells, formation of spermatangial parent cells, initiation of the carpogonial branch apparatus, and formation of tetrasporangial initials are homologous developmental processes that are documented for the first time in the type species of the economically important family Gracilariaceae, Gracilaria verrucosa (Hudson) Papenfuss from the British Isles. G. verrucosa is characterized by a supporting cell of intercalary origin that bears a 2‐celled carpogonial branch flanked by two sterile branches, direct fusion of cells of sterile branches onto the carpogonium, formation of an extensive carpogonial fusion cell through the incorporation of additional gametophytic cells prior to gonimoblast initiation, gonimoblast initials produced from fusion cell lobes, schizogenous development of the cytocarp cavity, inner gonimoblast cells producing tubular nutritive cells that fuse with cells of the pericarp or floor of the cystocarp, absence of cytologically modified tissue in the floor of the cystocarp, and carposporangial initials produced in clusters or irregular chains. Spermatangial parent cells are generated in flaments from intercalary cortical cells that line an intercellular space forming a ‘pit’ or ‘conceptacle’. Tetrasporangial initials are transformed from terminal cells derived through division of an outer cortical cell. Tetrasporangia are cruciately divided.The Gracilariaceae is removed from Gigartinales and transferred to the new order Gracilariales. Their closest living relatives appear to be agarophytes belonging to the Gelidiales and Ahnfeltiales.

Sphagnum aureum, a New Species from Costa Rica

Sphagnum aureum sp. nov. (section Sphagnum) is reported from high elevation peatlands in Costa Rica. This species is similar to S. alegrense and S. magellanicum, but differs from these species in branch leaf, stem leaf, and cortical cell morphology. While collecting bryophytes in Costa Rica, I found specimens of Sphagnum that represent a new species in section Sphagnum of the genus. SPHAGNUM AUREUM McQueen, sp. nov. (FIG. 1-8) Plantae pallido-auricolores, pallido-fuscae. Cellulae epidermidis caulinae stratis 3, fibrosae, parietibus exterioris cellularum superficialium foraminibus 1-2(-3) instructis, apice porosis ellipticis. Folia caulina plana, late lingulata, 1.0-1.4 mm longa; cellulae hyalinae breves, non septatae, non fibrosae, aporosae. Rami 4 in fasciculo. Folia ramulina 1.0-1.5 mm longa, ovata, concava; cellulae hyalinae dorso poris magnis in clelularum angulis, interiore folii superficie aporosae; cellulae chlorophylliferae sectione transversali ellipticae, intercellulas hyalinas perfecte mediae, utrinque inclusae. Plants pale gold, tan, or light-brown. Stem cortical cells in 3 layers, fibrillose, outer cortical cells with 1-2 (sometimes 3) pores, apical pore commonly elliptical. Stem leaves flat, lingulate, 1.0-1.4 mm long; hyaline cells short, undivided, without pores or fibrils. Branches in fascicles of 4 (2 spreading, 2 pendent). Branch leaves 1.0-1.5 mm long, oblong-ovate, deeply concave; hyaline cells of outer surface with pores in groups of 3 at adjacent angles and with a few singly at sides, inner surface aporose or with only a few pores; chlorophyllous cells elliptic in cross section, central, entirely included, hyaline cells slightly convex on both surfaces, with smooth inner walls. TYPE: COSTA RICA. In wet seep near lower limit of piramo of north face of Cerro de la Muerte, 3,250 m, Cyrus B. McQueen 4020 (holotype, vT; isotype, CR). This species resembles S. alegrense Warnst. and S. magellanicum Brid., but differs from both in a number of features (Fig. 1-8): S. aureum is pale gold, tan, or pale brown, without any red coloration as in S. magellanicum and S. alegrense. The chlorophyllose cells of the branch leaves are similar to those of S. magellanicum. Sphagnum aureum and S. magellanicum differ from S. alegrense, in that they lack the vermiform ridges on the inner side walls (Allen 1986; Crum 1980, 1984). Sphagnum aureum also has fibrillose cortical cells as in S. magellanicum, whereas those of S. alegrense are efibrillose. Some other unique features of S. aureum are that on the inner surface the branch leaf hyaline cells are aporose or have only a few pores. The stem leaves of anisophyllous plants are about half the length of those of S. magellanicum. The pores of the cortical cells are also different from those of S. magellanicum and S. alegrense in that there are 2 pores (rarely 3) per cell and the upper pore of each cell is elliptic in shape. The anisophyllous plants of S. aureum that I collected were growing at the lower limit of the pairamo of Cerro de la Muerte. The plants formed small, tightly compact hummocks at the bases of stands of bamboo and small cushions on the edges of eroded stream banks. The pH of standing water around the S. aureum populations ranged from 3.95 to 4.95 (based on seven samples). Sporophytes were found on some plants in each of the small hummocks and cushions that I found. Other species growing in the type locality include S. alegrense, S. magellanicum, S. meridense (Hampe) C. Miill., S. sparsum Hampe, and S. perichaetiale Hampe.