New Insights into Plagiogrammaceae (Bacillariophyta) Based on Multigene Phylogenies and Morphological Characteristics with the Description of a New Genus and Three New Species

Plagiogrammaceae, a poorly described family of diatoms, are common inhabitants of the shallow marine littoral zone, occurring either in the sediments or as epiphytes. Previous molecular phylogenies of the Plagiogrammaceae were inferred but included only up to six genera: Plagiogramma, Dimeregramma, Neofragilaria, Talaroneis, Psammogramma and Psammoneis. In this paper, we describe a new plagiogrammoid genus, Orizaformis, obtained from Bohai Sea (China) and present molecular phylogenies of the family based on three and four genes (nuclear-encoded large and small subunit ribosomal RNAs and chloroplast-encoded rbcL and psbC). Also included in the new phylogenies is Glyphodesmis. The phylogenies suggest that the Plagiogrammaceae is composed of two major clades: one consisting of Talaroneis, Orizaformis and Psammoneis, and the second of Glyphodesmis, Psammogramma, Neofragilaria, Dimeregramma and Plagiogramma. In addition, we describe three new species within established genera: Psammoneis obaidii, which was collected from the Red Sea, Saudi Arabia; and Neofragilaria stilus and Talaroneis biacutifrons from the Mozambique Channel, Indian Ocean, and illustrate two new combination taxa: Neofragilaria anomala and Neofragilaria lineata. Our observations suggest that the biodiversity of the family is strongly needed to be researched, and the phylogenetic analyses provide a useful framework for future studies of Plagiogrammaceae.     

TAXONOMY OF ADAMSIELLA L.E. PHILLIPS ET W.A. NELSON,GEN. NOV. AND EPIGLOSSUM KÜTZING (RHODOMELACEAE,CERAMIALES)1

In a taxonomic/phylogenetic study of the genus Lenormandia, several species were found to differ significantly from the type species, L. spectabilis Sonder, in apical morphology, blade‐surface pattern, medullary construction, the presence of pseudopericentral cells, and the position of reproductive structures. These species constitute two groups that differ morphologically, a finding largely supported by analysis of 18S rRNA sequences, as reported previously. The two putative Lenormandia species from New Zealand, along with two previously undescribed species also from New Zealand, comprised one such group, designated here by the new genus name Adamsiella L.E. Phillips et W.A. Nelson, gen. nov. and including A. melchiori L.E. Phillips et W.A. Nelson, sp. nov., A. lorata L.E. Phillips et W.A. Nelson, sp. nov., A. angustifolia (Harvey) L.E. Phillips et W.A. Nelson, comb. nov., and A. chauvinii (Harvey) L.E. Phillips et W.A. Nelson comb. nov. Adamsiella differs from Lenormandia by incurved apices, a chevron surface pattern, and reproductive structures on dorsi‐ventrally flattened apically incurved polysiphonous branchlets usually produced at the margins. Two species endemic to Australia formed the second group designated by the resurrected generic name Epiglossum and also characterized by a strongly incurved apex and chevron surface pattern but with reproductive structures produced on terete polysiphonous branchlets found either on the midrib or elsewhere on the blade surface but not the margins. Epiglossum contains E. smithiae (J.D. Hooker et Harvey) Kützing and E. proliferum (C. Agardh) L.E. Phillips, comb. nov.     

亚轮生奇异蕨(Adoketophyton subverticillatum)在贵州都匀泥盆系蟒山群的发现及其意义

Adoketophyton subverticillatum (Li et Cai) Li et Edwards (亚轮生奇异蕨)是云南早泥盆世坡松冲植物群中颇具代表性的、研究较为详细的一种植物, 目前对其整体形态特征和解剖结构都有较深入的认识。本文通过系列针修法, 将采自贵州都匀包阳剖面蟒山群下段的一块植物化石新材料归入A. subverticillatum。基于目前对 Adoketophyton时空分布的认识, 认为该属可作为早泥盆世植物群的代表分子, 并据此推断蟒山群下段的时代应为早泥盆世。Adoketophyton subverticillatum在都匀的发现, 表明贵州都匀蟒山群中的植物与云南坡松冲植物群在属、种一级上存在扩散与交流现象。Adoketophyton以及其他相关植物的研究表明, 在高大气CO₂浓度的早泥盆世, 叶性结构如孢子叶、苞片、枝叶复合体等已广泛分布于华南板块。     

Morphology of Laurencia clavata and L. elata (Ceramiales,Rhodophyta) in relation to generic circumscription in the Laurencia complex

Laurencia Lamouroux (Rhodophyta) was recently separated into three genera–Laurencia, Chondrophycus (Tokida et Saito) Garbary et Harper and Osmundea Stackhouse – each of which was newly defined based on vegetative and reproductive structures. In this study, the previously unknown vegetative and reproductive morphology of two Australian endemic species of Laurencia, L. clavata Sonder and L. elata (C. Agardh) Harvey, was studied, particularly in the context of the revised generic delineation. These species exhibit vegetative axes with four pericentral cells and trichoblast-type spermatangial development. Tetrasporangia are abaxially produced from the existing third and fourth pericentral cells. L. clavata has terete thalli with distinctive verticillate branching and is similar to Chondria C. Agardh, rather than to Laurencia, in having an unusually marked constriction at the base of the branches and starch accumulation in subcortical and medullary cells. Compared to Laurencia, apical cells of this species exhibit a less oblique division ; the resulting recognizable axial cell rows extend somewhat below the branches, and particularly at a young stage they are also clear throughout branchlets. However, other vegetative and spermatangial structures show that L. clavata is more closely allied to Laurencia than to Chondria, and it is placed in Laurencia. By contrast, L. elata exhibits morphology typical of Laurencia and is characterized by large, robust, compressed thalli with fastigiately distichous branching and an extensive secondary cortex. Furthermore, it appears to be distinct from similar species in sometimes having a parasitic species of Janczewskia Solms-Laubach (Rhodophyta). Taxonomy of Laurencia is discussed on the basis of these and previous studies.     

ON PHENOTYPIC EXPRESSION,MORPHOGENETIC PATTERN AND SYNANGIUM EVOLUTION IN PSILOTUM

Both the typical form and the appendageless variant of Psilotum nudum produce terminal synangia at the ultimate tips of the aerial axes. One clone in particular of the typical appendaged form produced synangia entirely at the tips of the aerial branches, as in the appendageless variant, and also developed occasional lateral transitional entities on the upper aerial axis displaying appendagelike and axislike morphological qualities. A developmental comparison of synangium development at the ultimate tips of aerial branches and of unusually elongating and normal sized fertile-appendages showed that the morphogenetic pattern of synangium development was similar. Anatomical and morphological evidence showed the synangium to be derived from terminal subdivisions or bifurcations of the apical meristem of each structure studied. This supports the phyletic concept that the synangium of the Psilotaceae is basically terminal to an axis or an axis homologue, and that it probably evolved from terminal bifurcative branching. Occasional multiple sporangium lobes may be formed on a P. nudum synangium which may not be represented by vascular bundles. Two hypothetical phyletic models of synangium evolution are proposed that could be used to explain this phenomenon and which should be tested by further evidence. Typical and appendageless P. nudum were compared in their morphogenetic pattern developed at the upper axis vegetative apical meristem, and a reconciliation was made between the structuring of the apparently disparate forms, which involved the presence or absence of serial ordering in apical derivatives. It is suggested that this could serve as a model for appendage evolution in the family Psilotaceae.     

Afrocymbella barkeri sp. nov. (Bacillariophyta), a common phytoplankton component of Lake Challa,a deep crater lake in East Africa

A new freshwater diatom, Afrocymbella barkeri Cocquyt & Ryken sp. nov., is described from Lake Challa, a deep and unproductive crater lake near Mt Kilimanjaro in equatorial East Africa, based on light and electron microscopic observations. This tropical diatom is a representative of the rather small genus Afrocymbella with only 12 known species and with a distribution restricted to the African Rift. Taxa belonging to this genus are heteropolar and characterized by dorsiventral valves curved along the pervalvar axis and the presence of small pseudosepta and septa on the open girdle bands. Afrocymbella barkeri was common only towards the end of the dry and windy season corresponding to northern hemisphere summer, when deep water-column mixing caused upwelling of nutrient-rich water from the hypolimnion. This taxon was observed free living in the water column during mixing, but the presence of a small apical pore field at the foot pole, along with some cells with mucilage stalks, suggests that its primary habitat probably involves attachment to a substrate.     

Primary Root Growth and the Pattern of Root Apical Meristem Organization are Coupled

Root apical meristems (RAMs) in dicotyledonous plants have two organizational schemes; closed (with highly organized tiers) and open (tiers lacking or disorganized). These schemes are commonly believed to remain unchanged during the growth of the root axis. Individual roots are commonly thought to have indeterminate growth. We challenge these two generalizations through the study of five species with closed apical organization: Clarkia unguiculata L., Oxalis corniculata L., Dianthus caryophyllus L., Blumenbachia hieronymi Urb., and Salvia farinaceae Benth. cv. “Strata”. These roots have phased growth patterns where early growth is followed by deceleration, after which the initial cells stop dividing, elongation ceases, and the root reaches its determinate length. At or before reaching determinacy, the root apical meristem stops maintaining its closed organization and becomes less organized. These observations will be placed in context with observations from the literature to suggest two new generalizations, namely, that apical organization does change over the growth phases of roots, and that roots are determinate.     

Morphology of Chondrophycus undulata and C. parvipapillata and its implications for the taxonomy of the Laurencia (Ceramiales,Rhodophyta) complex

Laurencia Lamouroux subgenus Chondrophycus Tokida et Saito was recently raised to generic status as Chondrophycus (Tokida et Saito) Garbary et Harper (Ceramiales, Rhodophyta). The previously unknown morphology and anatomy of two Chondrophycus species, C. undulata (Yamada) Garbary et Harper and C. parvipapillata (C.K. Tseng) Garbary et Harper, were studied in specimens from Korea, Japan and Hawaii. These species share some features, such as a strongly compressed thallus, vegetative axes with two pericentral cells, tetrasporangial production from pericentral cells and spermatangial development of the trichoblast type. However, they differ from each other in the position of the first pericentral cell relative to the trichoblast in axial segments and in the position of the tetrasporangial pericentral cell. In C. undulata, the first pericentral cell is always produced at one side of the basal cell of a trichoblast, whereas in C. parvipapillata it is formed underneath this cell. While tetrasporangia in C. undulata are produced only from three (occasionally four) additional pericentral cells, in C. parvipapillata they are formed by the existing second pericentral cell and two (occasionally three) additional pericentral cells, so the resulting tetrasporangial axial segment has only one sterile pericentral cell rather than two as in C. undulata. C. undulata produces spermatangial branches from two laterals on the suprabasal cell of trichoblasts but one of the two remains partly sterile, whereas in C. parvipapillata a spermatangial branch develops from only one of the two laterals. These two species also differ distinctly from each other in some vegetative features, such as presence or absence of (1) secondary pit connections between epidermal cells, (2) a palisade structure of epidermal cells with conical projections and (3) corps en cerise. The taxonomic implications of these vegetative and reproductive features of Chondrophycus and those of other genera of the Laurencia complex necessitate changes to the generic delineations of Osmundea Stackhouse, Laurencia and Chondrophycus. The required new combinations in Chondrophycus are made, mainly for species from the western Pacific. An infrageneric classification scheme is also proposed for Chondrophycus including Kangjaewonia subgen. nov., Palisada (Yamada) subgen. stat. nov., Yuzurua subgen. nov. and Parvipapillatae sect. nov.     

Coremiella cuboidea (Sacc. et Ell.) Cif. et Car. n. comb. isolata da feci umane

Riassunto Sono studiati nelle loro caratteristiche morfo-culturali e biologiche quattro ceppi omogenei diCoremiella isolati da feci umane. Questo genera è simile aGeotrichum ma oltre a cellule miceliche clamidosporo-simili presenta formazione apicali miceliche di tipo coremioide reptante.L'artrosporulazione è un processo endogeno come inGeotrichum, e come inGeorichum si hanno artrospore clamidosporioidi fertili opache e artrospore usuali non fertili e jaline, ma meno differenziate.I ceppi vengono riferiti aC. ulmariae e le caratteristiche vengono paragonate anche con le culture su legno diSpirea ulmaria.Il primo esemplare diCoremiella è stato pubblicato comeOospora cuboidea Sacc. etEll. come è stato accertato studiando l'esemplare autentico diEllis.In conclusione il genereCoremiella Bub. etKrieg. è stato emendato ed è stata creata la combinazioneC. cuboidea (Sacc. etEll.).

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Summary Four homogeneous strains ofCoremiella from human feces were studied from morpho-cultural and biological standpoint. This genus is likeGeotrichum, but in addition to some mycelial, chlamydospore-like cells, coremioid mycelial, reptant strands are formed.The arthrosporulation is an endogeneous process, and, likeGeotrichum, there are usual hyaline and duller chlamydosporioid, fertile arthrospores, but less differentiated.The strains are referred toC. ulmariae, and the characteristics were compared also on timber and woody European Meadowsweet cultures. But the first binomial ofCoremiella has been published asOospora cuboidea Ell. etSacc., as ascertained by the study of the authenticEllis specimen.In conclusion, the genusCoremiella Bub. etKrieg. has been emended, and the combinationC. cuboidea (Sacc. etEll.) established.

     

rbcL gene sequences reveal relationships among north-east Pacific species of Porphyra (Bangiales, Rhodophyta) and a new species, P. aestivalis

Phylogenetic analyses of the rbcL (chloroplast Rubisco large subunit) gene from 23 newly sequenced species of Porphyra, primarily from the north‐east Pacific, one Bangia and previously published sequences from both genera resolve relationships among most species of Porphyra and reveal five clades of species with Porphyra‐type morphologies among a number of Bangia lineages: (1) P. papenfussii V. Krishnam; (2) P. mumfordii S. C. Lindstrom et K. M. Cole and P. rediviva Stiller et Waaland together with a group of north Atlantic species, including the type of the genus, P. purpurea (Wahl‐enb.) C. Agardh; (3) P. cuneiformis (Setch. et Hus) V. Krishnam., P. occidentalis Setch. et Hus, P. schizo‐phylla Hollenb., and P. variegata (Kjellm.) Kjellm. and their Atlantic sibling species, all distromatic; (4) P. aestivalis sp. nov. and its north Atlantic sibling, P. birdiae C. D. Neefus et A. C. Mathieson; and (5) a speciose clade containing both Pacific and Atlantic representatives. Close relationships are confirmed between sibling species previously identified by iso‐zymes, morphology and chromosomal features. The morphologically similar dioecious P. pseudolanceolata V. Krishnam., P. conwayae (S. C. Lindstrom et K. M. Cole) stat. nov., and P. lanceolata (Setch. et Hus) G. M. Smith occur in a strongly supported subclade in clade 5 together with the monoecious P. fallax S. C. Lindstrom et K. M. Cole. Results presented here highlight the need for intensive taxon sampling and for examination of different parts of the genome to understand more fully relationships among species and higher level taxa in the Bangiales.     

FRESHWATER HYPHOMYCETES OF THE NORTHERN APPALACHIAN HIGHLAND INCLUDING NEW ENGLAND,AND THREE COASTAL PLAIN STATES

Twenty-seven species of freshwater Hyphomycetes from two five-state areas in the northern Appalachian Highland, New England, and three Coastal Plain states were collected, isolated, and identified. The spores of three fungi which are probably aquatic Moniliales were also studied. Sigmoidea, a new Hyphomycete genus, includes submerged aquatic fungi which produce phialides laterally along the mycelium and sigmoid, multicellular phialospores. Varicosporium giganteum sp. n. produces terminal, hyaline, branched, and multiseptate aleuriospores. The main spore axis has one to four lateral branches which arise successively on one side of this axis. Tricladium marylandicum sp. n. is similar to T. splendens in that the lateral branches are constricted where each branch joins the main spore axis. It differs from this species in that the spore has a blunt apical cell on the main axis and on each of the lateral axes. Three possible methods of dispersal are presented to explain the cosmopolitan distribution of freshwater Hyphomycetes.     

Ultrastruttura della cellula apicale di Halopteris scoparia (L.) Sauvageau (Phaeophyceae,Sphacelariales)

Abstract

Ultrastructure of the apical cell of Halopteris scoparia (L.) Sauvageau (Phaeophyceae, Sphacelariales). - The ultrastructure of resting apical cells of Halopteris scoparia (L.) Sauvageau from material collected in December is described. The cytoplasm is higly vacuolated with lipids, poliphenolic substances and polisaccharides occurring inside the vacuoles (the classic « physodes »).

Two cell organelles are prominently active at this stage: conspicuosly hypertrophic dictyosomes and the budding endoplasmic reticulum. Both light and electron microscope observations show that the cell wall has an outer stratification and inner discontinuous thickenings, the constituent material of which is uniformerly dispersed.

The above observations point out that the apical cell of Halopteris scoparia at this stage of its life cycle is engaged in an elaboration of vacuolar and parietal substances which will be therefore readly available at the outset of the growing season.     

PARMALES (CHRYSOPHYCEAE) FROM THE GULF OF TEHUANTEPEC,MEXICO, INCLUDING THE DESCRIPTION OF A NEW SPECIES,TETRAPARMA INSECTA SP. NOV., AND A PROPOSAL TO THE TAXONOMY OF THE GROUP1

There are few studies dedicated to species of the Order Parmales all over the world. All 12 taxa described are part of the marine ultraplankton (less than 5 μm). Analysis of filtered samples from the Gulf of Tehuantepec yielded specimens of two taxa of the group. One is a new species, belonging to the genus Tetraparma. Tetraparma insecta sp. nov. is solitary and spherical (2.8–3.8 μm diameter), and all plates lack ornamentations or knobs, the walls are smooth, and only the plate junctions are seen. The shield plates are convex and show a conspicuous rim, some of them with an indentation. This species shows superficial similarities with Tetraparma pelagica, the other species described of the genus, and is very similar to siliceous forms, previously found, with no formal name. The other species is the taxon Triparma laevis form mexicana (Kosman) stat. nov., earlier described for Mexican waters, which has an irregular ala, the shield plates have knobs at the center, the triradiate plates show a “Y”‐shaped keel, and the walls of plates and ala show minute granules. Tetraparma insecta was distributed widely in the study area and was relatively abundant, reaching a density of 4 × 10⁴·L^?1, with an evident preference for subsurface waters (10–20 m depth), whereas T. laevis form mexicana was rare and scarce. Both species seem to be restricted to tropical–subtropical waters. We discuss the taxonomy of Parmales, especially concerning the category of subspecies within the group. Parmales is a widespread group in cold and tropical waters.     

Primary Root Growth and the Pattern of Root Apical Meristem Organization are Coupled

Root apical meristems (RAMs) in dicotyledonous plants have two organizational schemes; closed (with highly organized tiers) and open (tiers lacking or disorganized). These schemes are commonly believed to remain unchanged during the growth of the root axis. Individual roots are commonly thought to have indeterminate growth. We challenge these two generalizations through the study of five species with closed apical organization: Clarkia unguiculata L., Oxalis corniculata L., Dianthus caryophyllus L., Blumenbachia hieronymi Urb., and Salvia farinaceae Benth. cv. Strata. These roots have phased growth patterns where early growth is followed by deceleration, after which the initial cells stop dividing, elongation ceases, and the root reaches its determinate length. At or before reaching determinacy, the root apical meristem stops maintaining its closed organization and becomes less organized. These observations will be placed in context with observations from the literature to suggest two new generalizations, namely, that apical organization does change over the growth phases of roots, and that roots are determinate.     

Morphology and life history of Scytosiphon canaliculatus comb. nov. (Scytosiphonales,Phaeophyceae) from Japan*

Morphology of field material and life history in culture were studied in Scytosiphon canaliculatus (Setchell et Gardner) comb. nov. from northern Japan. Erect gametophytes of S. canaliculatus are cylindrical, tubular, up to 7 mm wide and 40 cm long, and without regular constrictions. S. canaliculatus has pronounced anisogamy and ascocysts accompanied with plurilocular gametangia. The life history of S. canaliculatus showed an alternation between erect gametophytes and crustose prostrate sporophytes bearing unilocular sporangia. Since field sporophytes of S. canaliculatus were found to be identical with Hapterophycus canaliculatus Setchell et Gardner (Ralfsiaceae, Phaeophyceae), it is proposed to transfer H. canaliculatus to the genus Scytosiphon. In the field, gametophytes with plurilocular gametangia appeared in spring and disappeared in summer. Sporophytes with unilocular sporangia were collected in late autumn and winter. Unilocular sporangia were produced at 15°C in short-day culture conditions and unispores developed into erect gametophytes at 5–15°C. It is suggested that the seasonal Occurrence of gametophytes in the field is due to the seasonal formation of unilocular sporangia, which is regulated by temperature and photoperiod.     

STRUCTURE AND HISTOGENESIS OF THE EMBRYO OF ACER SACCHARINUM. I. EMBRYO SAC AND PROEMBRYO

Structure of the embryo sac and development of the proembryo of Acer saccharinum L. are described from paraffin sections. The embryo sac is monosporic and identical to the 8-nucleate Polygonum type in all respects. Cell, nuclear, and nucleolar sizes are constant within a narrow range and sharply distinctive for all components of the mature sac. Polar nuclei fuse before double fertilization. The longitudinal axis of symmetry of the egg, zygote, and proembryo is variously oriented with respect to the longitudinal axis of the embryo sac and is determined by the point of attachment of the presumptive egg cell to the sac wall. Subsequent development of the young embryo is responsive to aligning factors within the embryo sac and is collateral with the longitudinal axis of the sac. The first segmentation is transverse to the longitudinal axis of the zygote; the second and third are transverse in the basal cell and longitudinal in the apical cell. Descendants of ci form a short irregular suspensor; ca and m give rise to the apical and basal halves respectively of the embryo proper. The contribution of the proembryonic tiers to the older embryo differs in embryos of different initial orientation. Distribution and orientation of mitosis in the proembryo are shown in two accumulation maps.     

A model system to study the effect of SO2 on plant cells. III. Effects of sulfite on the ultrastructure of fern protonemal cells

The mechanism of the toxic effects on plant cells of sulfite, a product of the air pollutant sulfur dioxide, is not well understood. Therefore, changes in the fine structure and organization of microtubules and microfibrils induced by sulfite were studied by electron and light microscopy in the protonemata of the fernAdiantum capillusveneris L. Under red-light conditions, growing protonemata fumigated with 0.05 or 0.1 μ1/1 SO₂ for 1 to 4 days showed abnormalities, such as apical swelling, and they sometimes burst at the apex. The incidence of abnormalities seemed to be correlated with the concentration of the sulfite dissolved in the culture medium. At an appropriate concentration (3.3–6.6. mM) of sulfite (applied as K₂SO₃), cell swelling at the apical region of protonema was also induced. When the concentration of sulfite was as high as 6.6 mM, more than 60% of protonemata burst at the tip. During the apical swelling, no distinct changes were observed in the fine structure of organelles, such as the chloroplasts, mitochondria, microbodies, Golgi bodies and nucleus. However, the arrangement of cortical microtubules and that of the innermost layer of microfibrils around the subapical region of protonemata were changed from transverse to the cell axis (i.e., circular) to random and the cell wall was thickened. These observations suggest that sulfite may influence the mechanisms that maintain the transverse orientation of microtubules in the subapical region of a protonema and that the resultant random arrangement of microtubules induces the random arrangement of microfibrils and leads to apical swelling.     

Fine structure and 18S rDNA phylogeny of a marine araphid pennate diatom Plagiostriata goreensis gen. et sp. nov. (Bacillariophyta)

A marine araphid pennate diatom Plagiostriata goreensis is described from the sand grains of Goree Island, Dakar, Republic of Senegal, based on observations of fine structure of its frustule. The most striking feature of the species is its striation, which is angled at approximately 60° across the robust sternum. The other defining features of the species are its one highly reduced rimoportula and apical pores located at both ends of the valve margin. In the 18S rDNA phylogeny, the species appears as a member of a ‘small‐celled clade’ of araphid pennate diatoms that consist of Nanofrustulum, Opephora and Staurosira. The results of the phylogenetic analyses suggest that the distinct characters of the diatom; namely, oblique striae and apical pores, may have been acquired independently. However, it remains unclear whether the rimoportula of P. goreensis is a reduced state or P. goreensis acquired its morphologically curious rimoportula independently after the loss of an ancient rimoportula at the root of the small‐celled clade.     

Corynoplastis japonica gen. et sp. nov. and Dixoniellales ord. nov. (Rhodellophyceae,Rhodophyta) based on morphological and molecular evidence

A new unicellular red alga, Corynoplastis japonica gen. et sp. nov., is described from Tobishima, Japan. Cells are spherical, 18–33 µm in diameter, pale purple to brownish red and surrounded by a mucilaginous sheath. A single chloroplast with many lobes extends from the cell periphery to the cell center. A peripheral thylakoid is present. A pyrenoid occurs at each innermost chloroplast lobe end and one or two thylakoids are present in the pyrenoid matrix. The nucleus is eccentric to peripheral and Golgi bodies are scattered throughout the cell and associated with endoplasmic reticulum. Cells have a slow random gliding motility. The low molecular weight carbohydrate mannitol is present in the cells. Molecular phylogenetic analysis indicates that this alga is closely related to members of the genus Rhodella. A new order, Dixoniellales, is established for Dixoniella, Neorhodella and Glaucosphaera based on molecular and ultrastructural evidence (Golgi bodies associated only with the nucleus). The redefined order Rhodellales in which Rhodella and Corynoplastis are placed is characterized ultrastructurally by Golgi bodies scattered throughout the cytoplasm and associated with endoplasmic reticulum.