STRUCTURE AND AFFINITIES OF PROTOSTIGMARIA EGGERTIANA

Investigation of new, more or less complete specimens of Protostigmaria eggertiana reveals that it is a large, multilobed rooting structure produced at the base of a small arborescent lycopod. The trunk bears scars marking the point of attachment of leaves, and can be compared to the stem of Lepidodendropsis. In the largest specimens the root-bearing base is divided into about 13 lobes. In smaller, presumably younger specimens, fewer lobes are present. The roots are arranged on the lobes in series and orthostichies comparable to those of Isoetes. New observations on five- and six-lobed Isoetes plants reveal a closer correspondence between Protostigmaria and Isoetes than previously recognized; and support suspected homologies among many fossil and extant lycopsid rooting structures.     

中国产3种水韭叶舌形态结构的比较研究

以中国产3种水韭的成熟叶片基部为实验材料,采用石蜡切片法,详细观察3种水韭的叶舌结构,建立各自叶舌的立体模型,探讨3种水韭间的亲缘关系,并比较了中国特产水韭与中亚及北美水韭的演化关系。结果显示:(1)3种水韭叶舌结构主要分为舌片、舌足和横带三部分。(2)中华水韭与东方水韭舌片均为三叉型,有主侧舌片之分,足角均为卵圆形,舌足与叶轴平行,而云贵水韭长鼻形,无主侧舌片之分,足角为三角形,舌足与叶轴有一定的角度。(3)中华水韭与云贵水韭的舌足侧面观为长椭圆形,东方水韭舌足侧面观为肾形。研究认为,中华水韭与东方水韭的亲缘关系较近,二者与云贵水韭亲缘关系较远;叶舌是水韭类的溯祖形态,其结构复杂,特征稳定,种间差异明显,应该作为水韭分类的重要依据。     

MEGASPORE WALL ULTRASTRUCTURE IN ISOETES

In Selaginella, megaspore wall ultrastructure (unit morphology and arrangement) is correlated with taxonomic position. In some Pennsylvanian lycopods there is a correlation with dispersal strategy. This study was designed to assess any correlation between habitat preference and wall ultrastructure in Isoetes. Except for a few minor structural correlations, wall ultrastructure appears to be constant in terrestrial, amphibious, and aquatic species of Isoetes. Several distinct sizes of megaspores occur in some megasporangia and correspond to 1) full-size megaspores with siliceous coatings, 2) small megaspores with siliceous coatings, and 3) full-size megaspores without siliceous coatings. The uniformity in wall ultrastructure within modem Isoetes together with the lack of uniformity of fossil isoetalean megaspore wall ultrastructure suggest that the modem species of Isoetes are closely related.     

The quillworts (Isoetes) of India: distribution, endemism and species radiation

The genus Isoetes L. in India is represented by 14species, of which eight species are recognized as being local endemics [confinedto one particular phyto-geographical division (PGD)] while the remaining sixoccur in more than one PGD and are described as endemic to a wider range. Thelocal endemic species are Isoetes dixitei,Isoetes panchganiensis and Isoetessahyadriensis in Western Ghats region; Isoetespantii, Isoetes bilaspurensis, Isoetesreticulata and Isoetes tuberculata inChotanagpur Malwa Vindhya Plateau and Isoetes debii innortheastern India. The wider endemic species are Isoetespanchananii, Isoetes sampathkumaranii,Isoetes rajasthanensis, Isoetesmahadevensis, Isoetes indica andIsoetes coromandelina. Our studies on the patterns ofendemism suggest that the radiation of quillworts advanced from dry lowlandareas to the rainy uplands and mountains. Isoetescoromandelina is the first Indian quillwort to colonize in lowlandsof the coastal zone (Coromandel), from where it spread to different parts of thesub-continent and gave rise to new species. Thus this species is a key Indianspecies which has played an important role in the radiation of quillwort in thecountry and appeared as the connecting link among the quillwort flora of variousPGDs. The centres of diversity for almost all the presently known Indianquillworts species are recognized.     

THE RHIZOMORPH APEX OF PAURODENDRON; IMPLICATIONS FOR HOMOLOGIES AMONG THE ROOTING ORGANS OF LYCOPSIDA

A rhizomorph of Paurodendron with an intact apex recently has been discovered in Upper Pennsylvanian sediments of Ohio, and this provides the anatomical evidence necessary to interpret structure, ontogeny and homologies among lycophyte rooting organs. The basal meristem of Paurodendron is radial and lenticular, and produces an apical plug of parenchymatous tissue similar to a root cap. The plug is surrounded by a furrow associated with radially aligned cells that demonstrate a developmental correspondence to the furrow(s) of Isoetes. Based on external structural similarities at the rhizomorph apices of Paurodendron, Stigmaria, and young Nathorstiana, and on the anatomical similarities of Paurodendron to Isoetes, Stigmaria, Chaloneria, and Lepidocarpon embryos, all are interpreted as having a rooting organ that represents a modified shoot system that is fundamentally unlike the primary root system of seed plants. Likewise, the rootlets of rhizomorphic lycophytes are interpreted as leaves modified for rooting, and that have the equivalent of exogenous origin. As such, they are fundamentally unlike the adventitious roots of rhizomatous lycophytes like Lycopodium and Selaginella.     

中华水韭孢子囊发育研究

采用半薄切片法,连续观察了极度濒危级(CR)植物中华水韭大小孢子囊的发育过程,以期从无性生殖的角度,为探讨其濒危原因提供直观可靠的理论根据。结果显示:(1)中华水韭的大小孢子叶相间排列,无混生孢子囊。(2)隔丝为孢子供给营养,其体积直接影响孢子的大小、产量和育性。(3)大小孢子囊都近半数败育,小孢子囊为整齐发育,大孢子囊为不整齐发育。(4)大小孢子囊均无柄,且都不存在开裂结构,只有孢子囊壁腐烂后才能散播孢子。研究认为,中华水韭的濒危与孢子囊的发育特征密切相关,孢子囊的高频率败育、没有开裂结构以及对环境的依赖,是造成中华水韭濒危的重要因素之一;通过与近缘类群孢子囊的比较,发现仅水韭孢子的散播借助外力,对生境要求较高,即验证了水韭古老的系统学地位,同时说明水韭更具有监测生境地区环境指标的能力。     

云贵水韭雌配子体发育及其濒危机制的研究

为了解云贵水韭(Isoetes yunguiensis)的生殖过程和濒危原因,采用人工培养获得其雌配子体,用半薄切片法观察雌配子体发育过程。结果表明,云贵水韭的大孢子萌发率约为26%;雌配子体异养,终生都在大孢子细胞壁内发育;颈卵器发育只有2枚颈沟细胞而无腹沟细胞。雌配子体发育停止在游离核时期、颈壁细胞数量偏少或排列紊乱、颈沟细胞异常、卵细胞凋亡等可能是导致生殖濒危的原因。同时,游离核是水韭生殖生物学研究和系统学研究的重要环节之一;缺失腹沟细胞可能是水韭类简化性进化的特征之一。     

Casparian Strips in the Leaf Intrastelar Canals of Isoetes duriei Bory, a Mediterranean Terrestrial Species

Anatomical observations, using light and fluorescence microscopy,were made on leaves of Isoetes duriei to verify the presenceof casparian bands around the intrastelar canals. This peculiaranatomical feature, previously reported for some Isoetes species,is confirmed. The possible role of this endodermis-like structure,in the transport of water due to root pressure or in the accumulationof certain metabolites, is discussed in relation to the ecologicaland anatomical features of the species. Copyright 2000 Annalsof Botany Company Isoetes duriei, Lycopsida, Mediterranean, leaf anatomy, endodermis, casparian strips, fluorescence microscopy     

Two new species ofIsoetes (Isoetaceae) from Jeju Island, South Korea

We name and describe two new species,Isoetes jejuensis and I.hallasanensis, from Jeju Island, South Korea. These taxa are compared with related species in East Asia, including I.coreana andI. sinensis. The rugulate megaspore ornamentation ofI. jejuensis differs from those otherIsoetes species. Furthermore,I. hallasanensis varies fromI. asiatica in its microspore ornamentation and chromosome number, although both species have an echinate megaspore ornamentation. These new species are tetraploid (2n = 44), whereasI. coreana is hexaploid (2n = 66).     

Competition in microcosm between a clonal plant species (Bolboschoenusmaritimus) and a rare quillwort (Isoetessetacea) from Mediterranean temporary pools of southern France

Bolboschoenus maritimus, a clonal species, is locally invasive in Mediterranean temporary pools where it threatens endangered rare plant species such as Isoetes setacea. The combination of management modifications (grazing) and of the progressive accumulation of fine sediments in the pools contributed to the establishment of competitive perennial plants such as B. maritimus. The competitive advantage of B. maritimus on I. setacea has been studied in controlled conditions. The goal of this experiment was to assess the role of environmental conditions in the output of the competition between Bolboschoenus and Isoetes, notably hydrology and soil richness. For this purpose, Isoetes was cultivated alone (three individuals/pot) and with Bolboschoenus (three individuals of both species). The experiment was run with five replicates on six types of sediment (gradient of richness in sand/silt/clay) combined with three hydrological treatments (flooded, wet. and dry). The competitive advantage of Bolboschoenus was measured as the ratio of the production of Isoetes in mixture versus monoculture. The results showed that Isoetes was always outcompeted by Bolboschoenus. However, the competitive advantage of Bolboschoenus on Isoetes, was more related to hydrology than to soil richness. The competitive advantage of Bolboschoenus was very high in wet and flooded conditions and very low in dry conditions. This situation may lead to the extinction, medium-term, of the populations of I. setacea. The introduction of ovine grazing or of cut back practices in temporary pools could reduce the B. maritimus biomass and help toward the conservation of I. setacea populations. Guest editors: B. Oertli, R. Cereghino, A. Hull & R. Miracle Pond Conservation: From Science to Practice. 3rd Conference of the European Pond Conservation Network, Valencia, Spain, 14–16 May 2008     

PAURODENDRON,A RHIZOMORPHIC LYCOPOD

From middle Pennsylvanian coal balls collected in Kansas and Illinois the ligules and rhizomorph of Paurodendron have been illustrated. Assignment of Paurodendron to the Lycopsida is corroborated. Discovery of the root-bearing portion of this Carboniferous lycopod establishes a diminutive, phyletic line in the Paleozoic with rhizomorphs smaller than many species of Isoeles. Paurodendron resembles the selaginelloid line more closely than other rhizomorphic types. Anatomical comparisons of Paurodendron with roots and root-bearing structures of lycopods are made; the root-bearing and a representative leaf-bearing portion of Paurodendron fraiponti have been reconstructed. The specific diagnosis has been emended, and the three species described by Fry have been reduced to one.     

Distribution of basic diploid and polyploid species of Isoetes in East Asia

Aims Isoetes L. is an ancient, primitive genus of heterosporous lycopsids characterized by a strongly reduced plant. The genus occupies a unique position in plant evolution as the closest relatives of the famous tree lycopods. Hybridization and allopolyploid speciation as well as habitat preference are regarded as having played an important role in the evolution of the genus Isoetes. However, it is still uncertain what factors have impacted upon hybridization and allopolyploid speciation of the genus Isoetes. Our understanding of the origin, evolution and modern distribution pattern of Isoetes in East Asia would benefit from investigations into the relationship between the unique geographical location and topographic features and the existing fossil record in the region. Methods The chromosome number was determined from known 81 populations of 10 species of Isoetes in East Asia. The altitude was obtained in location of every population. T‐test was used to evaluate the altitude difference between diploid and polyploid populations. Data of Japanese Isoetes from Takamiya et al. was used in the study. Results There are 10 known species of Isoetes with four diploids and six polyploids in East Asia. The four diploid species (2n = 22) are found at high altitudes (mean altitude = 2649.67 ± 1396.16 m, n = 18) and isolated from each other. In contrast, the six polyploid species widely occur in low altitude regions (mean altitude = 182.62 ± 181.44 m, n = 63) and are partially sympatric. Highly significant differences (P < 0.001) were observed between the mean altitude of locations of populations of diploids and polyploids. Main conclusions The polyploidy speciations of Isoetes in East Asia might originate and develop from Holocene (Quaternary). The present pattern of distribution of Isoetes in East Asia is the result of allopatric speciation derived from vicariance, dispersal and combinations of both, and significantly correlative with the geological history and geographical changes. The change of altitude might have played an important role in allopolyploid speciation and the pattern of distribution of the genus Isoetes in East Asia by exerting a considerable influence on dispersal and hybridization opportunities of Isoetes species.     

SPECIAL PAPER: MERISTEMS AND EVOLUTION: DEVELOPMENTAL CORRESPONDENCE AMONG THE RHIZOMORPHS OF THE LYCOPSIDS

This paper deals with a comparison of the rooted axes (rhizomorphs) of Isoetes with those of Stigmaria, Pleuromeia and other fossil lycopsids from the standpoint of developmental correspondence. The objective is to present a mechanistic approach to the problem of evaluating possible interrelationships among the genera. The results complement those from other comtemporary approaches to the same problem. These main points are advocated: 1) The rhizomorphs of Isoetes and Stylites correspond. Because neither of these contains an apical meristem, neither corresponds to Stigmaria with respect to organization of the axis or root production. 2) Rooted portions of Isoetes and Pleuromeia correspond, although external lobing in Pleuromeia parallels lobing of the stele, whereas in Isoetes external lobing occurs between the lobes of the stele. In both cases, lobing of the stele is associated with root production. 3) Paurodendron rhizomorphs appear to correspond to Stigmaria developmentally with regard to the presence of an apical meristem and the arrangement of roots, but Paurodendron rhizomorphs are shorter. If several lines of root production were added to the vascular cambium of the kind of rhizomorph seen in Paurodendron, a plant part like the rooted portion of Pleuromeia could result. Further extrapolations of the Paurodendron form of growth are explored for their bearing on comparison of rhizomorphs among the lycopsids.     

Biosystematic studies on the genusIsoetes in Japan I. Variations of the somatic chromosome numbers

The somatic chromosome number of three Japanese species ofIsoetes, I. asiatica, I. japonica andI. sinensis, was determined in 199 individuals from 49 populations. The chromosome number ofI. asiatica was 2n=22, confirming previous reports. However,I. japonica andI. sinensis displayed a diversity in chromosome number. Six cytotypes, 2n=66, 67, 77, 87, 88 and 89, were found inI. japonica; 2n=67, 87, 88 and 89 are new counts in the genusIsoetes. The plants with 2n=66 were the most frequent (72% of total individuals examined) and were distributed throughout Honshu and Shikoku. The plants with 2n=88 occurred in western Honshu and a limited region in northeastern Honshu where the plants with 2n=77 were also found. In contrast, four cytotypes, 2n=44, 65, 66 and 68, were found inI. sinensis. The chromosome numbers ofI. sinensis were reported here for the first time. The plants with 2n=44 occurred only in Kyushu, while the plants with 2n=66 were found throughout a large area of western Japan.     

A community of submerged aquatic CAM plants in Lake Kalgaard,Denmark

The CO₂ exchange pattern of leaves of dominant Isoetes lacustris L., Littorella uniflora (L.) Aschers. and Lobelia dortmanna L. from oligotrophic, carbon-poor Lake Kalgaard, Denmark was examined by gas-exchange experiments and by following the diurnal acidity rhythm. Both variables suggest Crassulacean Acid Metabolism (CAM) in Littorella and Isoetes. During the dark, both species had a continuous, but declining CO₂ uptake. The maximum uptake in Littorella was 28 μmol CO₂ g^?1 DW h^?1 or about 36% of the light CO₂ assimilation rate. In Isoetes, corresponding figures were 19 μmol CO₂ g^?1 DW h^?1 and 22%.A peak of 49.5 μEq g^?1 FW titratable acidity (Littorella) and 41.9 μEq g^?1 FW (Isoetes) was found at the end of the dark period, reflecting an increase of 11.6 μEq g^?1 FW (9 h)^?1 (Littorella) and 16.3 μEq g^?1 FW (9 h)^?1 (Isoetes). These results agreed with the cumulative CO₂ assimilation during the dark.The assimilation of CO₂ in the dark is important, apparently, for growth of Littorella and Isoetes in Lake Kalgaard. Lobelia, which exhibits little dark CO₂ assimilation, is also the least abundant species, at less than 1% of the total cover.     

The effect of CCCP on ion fluxes in the stele and cortex of maize roots

Summary The accumulation of ⁸⁶Rb labelled potassium by isolated stelar and cortical tissues from 7-day-old roots of Zea mays has been compared with the levels accumulated by these tissues in the intact root. Cortical tissues have similar uptake eapacities in these two conditions whereas stelar tissues only exhibit an uptake capacity in the intact root system. The uncoupler carbonylcyanide m-chlorophenylhydrazone caused a considerable decrease in the uptake of potassium by these tissues. In the intact root system it prevented ions from the bathing medium reaching the stelar tissues. The efflux pattern from preloaded isolated stelar and cortical tissues was considerably altered by the inhibitor, a promotion of the efflux occurring in both of these tissues.It is concluded that stelar tissues only accumulated ions when these are supplied through the root symplasm and that the stelar plasmalemma has only a limited uptake capacity per se. Stelar uptake is thus a reflection of vacuolar accumulation across the tonoplast. There is no evidence in the present study of a carrier-mediated active secretion of ions across the stelar plasmalemma. The fact that the efflux was promoted rather than depressed by the uncoupler supports the postulate that a passive leakage is the final stage in the transport of ions across the plant root.     

The macrophytic vegetation of Loch Urigill and other lochs of the Ullapool area

Summary

From the 15 lochs examined at altitudes between 9 and 267 m in western Sutherland and Wester Ross, a few areas of tall fen (with Hippuris, Sparganium erectum, Osmunda etc.) survive to indicate its potential distribution. Predominant grazed fen comprises patches of short Juncus articulatus and Carex nigra. Reedswamp is scarce, being dominated by Eleocharis palustris, Carex lasiocarpa and Schoenoplectus lacustris and, rarely, by Phragmites and Sparganium erectum. Floating-leaved vegetation was only encountered twice. Submerged vegetation to water depths of at least 1 m consists in the main of sparse Lobelia-Littorella with Juncus bulbosus, typical of the prevailing stony shores in every loch. Extensive Isoetes lacustris meadows may occur beyond that, with Potamogeton praelongus or P. perfoliatus stands in waters of alkalinities over 0·45 m-equiv 1^-1, reaching depths of 3 m in Loch Urigill. Loch Urigill is unusual in having dominant Isoetes at a water alkalinity of 0·76 m-equiv 1^-1 along with abundant Anabaena species and some Potamogeton filiformis.