Reaction-diffusion models of growing plant tips: bifurcations on hemispheres

We study two chemical models for pattern formation in growing plant tips. For hemisphere radius and parameter values together optimal for spherical surface harmonic patterns of index l = 3, the Brusselator model gives an 84% probability of dichotomous branching pattern and 16% of annular pattern, while the hyperchirality model gives 88% probability of dichotomous branching and 12% of annular pattern. The models are two-morphogen reaction-diffusion systems on the surface of a hemispherical shell, with Dirichlet boundary conditions. Bifurcation analysis shows that both models give possible mechanisms for dichotomous branching of the growing tips. Symmetries of the models are used in the analysis.     

A new species of Cycas (Cycadaceae) from Karnataka,India

Cycas swamyi Singh & Radha, sp. nov. (Cycadaceae) is described and illustrated from Karnataka, India. This new species has been confused with Cycas circinalis L., which is found in the Western Ghats. However, on the basis of its habit, characteristic isotomous‐type dichotomous branching, pinnae anatomy, mega‐ and microsporophyll morphology and seed anatomy, it has been segregated from C. circinalis and is described here as a new species. The distribution and conservation status are also discussed. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158 , 430–435     

DEVELOPMENTAL STUDY OF BRANCHED RHIZOPHORES IN THREE SELAGINELLA SPECIES

A morphogenetic investigation was made of the rhizophore of three large-sized tropical Selaginella species. The rhizophores of Selaginella delicatula, S. caudata, and S. plana arise exogenously at the points of branching of the main stems. In S. delicatula they are initiated at the junction of the second youngest branching. The rhizophore apical meristem has a tetrahedral apical cell and is capless. The rhizophores are usually three or four times dichotomously branched in S. delicatula and S. plana and four or five times in S. caudata. In S. delicatula, dichotomous branching of the rhizophore involves formation of two new apical cells subsequent to loss of an original apical cell. A pair of roots is formed endogenously from inner cells below the dermal layer at the apex of ultimate rhizophore branches. The finding that the rhizophore is an autonomously branched, leafless, and capless axis leads us to argue that Selaginella rhizophores, like lepidodendrid rhizomorphs, are fundamental axial organs that coordinate with the stem and root.     

HOMOPLOID RETICULATE EVOLUTION IN HELIANTHUS (ASTERACEAE): EVIDENCE FROM RIBOSOMAL GENES

Phylogenetic relationships among the 21 taxa comprising Helianthus sect. Helianthus and three outgroup species were assessed by restriction site mapping of the 18S-25S nuclear ribosomal RNA gene family. Wagner parsimony analysis of the 41 restriction site or length mutations observed produced a single 59-step most parsimonious tree. This tree was then compared to a cytoplasmic-based plastid phylogeny for this group. Several major discrepancies were observed between the two phylogenies suggesting both recent and ancient introgression. Furthermore, three cases of diploid hybrid speciation are unambiguously documented and a fourth case is suggested. These data are interpreted to suggest that evolution in Heliathus is reticulate rather than exclusively dichotomous and branching.     

Über den Verzweigungsvorgang beiPsilotum undSelaginella mit Anmerkungen zum Begriff der Dichotomie

After a critical evaluation of the concept of dichotomous branching in Cormophytes the shoot apical meristems ofPsilotum triquetrum andSelaginella speciosa are described. InPsilotum only the terminal meristems of the cryptophilic shoots have a three sided apical cell. Those of the photophilic shoots lack a typical apical cell.Selaginella has a two sided apical cell. The process of branching is independent from apical cells. It is due to an equal or unequal fractionation of the initial zone of the shoot apex which embraces all tissues above the leaf producing zone of the apical meristem.

Herrn Univ.-Prof. Dr.Walter Leinfellner zum 70. Geburtstag gewidmet.     

Developmental anatomy of the shoot apical cell,rhizophore and root ofSelaginella uncinata

The developmental anatomy of the shoot apex, rhizophore and root ofSelaginella uncinata was examined by the semi-thin section method. The shoot apex has a single, lens-shaped apical cell with two cutting faces. Rhizophore primordia are initiated exogenously at the branching point of the second youngest lateral shoot. The rhizophore apex has a tetrahedral apical cell with three cutting faces. A pair of root primordia is initiated endogenously from inner cells of the rhizophore apex, after the rhizophore apical cell becomes unidentifiable losing its activity, and subsequently a root cap is formed from the distal face of the root apical cell. During the course of successive root branching the apical cell in an original root apical meristem becomes unidentifiable and then a new apical cell is initiated in each of the bifurcated root apical meristems. The root branching mode seems to be equivalent to the described dichotomous branching mode of fern shoots. Our results demonstrate a distinct morphogenetical difference between the rhizophore and the root, and confirm the exogenous origin of the rhizophore, as described for other species ofSelaginella. This evidence indicates that the rhizophore is not an aerial root but a leafless, root-producing axial organ.     

Anomalous branching patterns in some fossilFilicales: Implications in the evolution of the megaphyll and the lateral branch,habit and growth pattern

From middle Carboniferous coal balls leaves and stems of structurally preserved Filicalean ferns (Psalixochlaenaceae, Botryopteridaceae) are described that deviate from the normal pattern of branching. From this, interpretations are made as to the origin and relationship of axillary branching and dichotomy in this line of ferns. Their megaphylls apparently have orginated from a three-dimensional dichotomous branching system. This is inferred from the widespread occurrence of short, leafy epiphyllous buds on their fronds and is related to their habit where the leaf often plays the dominant role and effects vegetative propagation.     

Development of appressoria on conidial germ tubes of <Emphasis Type="Italic">Erysiphe</Emphasis> species

Modes of branching of appressoria on conidial germ tubes of 36 Erysiphe spp. were studied. Only unlobed appressoria, termed alobatus pattern, were seen in E. lonicerae, E. magnifica and E. symphoricarpi. Viewed from above with light or scanning electron microscopes, other species had ± irregular lobing, but from below in the plane of contact with the substrate successive dichotomous branchings at 120° were seen to produce a five-lobed appressorium within 6 h. Each division produced a temporarily dormant outward-facing lobe and an inward limb that continued growth and division to form the axis of curved, hooked, single- or double-headed symmetrical or asymmetrical structures in a helicoid cyme-like pattern. Outlines of extracellular material after removal of germinated conidia confirmed this manner of branching. After 36 h some lobes re-divided forming botryose or jigsaw patterns even extending with extra appressoria to form candelabra-like structures. Conidia developed only one true germ tube; rarely secondary unswollen tubes emerged from spare shoulders or ends. The same true germ tubes developed initially on host surfaces, where secondary tubes and/or extensions from appressorial lobes grew into colony-forming hyphae. Lobed appressoria of Neoerysphe and Phyllactinia also branched at 120°. Podosphaera xanthii exhibited a simpler branching pattern.     

Astogenese vonAulopora cf.enodis Klaamann 1966Visby-Mergel, Silur von Gotland

This paper deals with bifurcation angle of a reptant, dichotomously branchingAulopora cf.enodis colony (Silurian, Gotland). It can be demonstrated, that during early astogenetic growth the branching angle between offsetting corallites decreases rapidly from 165° to 100° averagely during later growth stages. This growth pattern resembles development of similar dichotomous branching uniseral bryozoans, e.g. PaleozoicCorynotrypa species or MesozoicStomatopora species.     

Embryonic growth and trophotaenial development in goodeid fishes (Teleostei: Atheriniformes)

Embryonic growth and trophotaenial development are examined in two species of goodeid fish, Ameca splendens and Goodea atripinnis. During gestation of A. splendens, embryonic dry mass may increase from 0.21 mg at the onset of development to 31.70 mg at term. In G. atripinnis, embryonic dry mass ranges from 0.25 mg at the onset of development to 3.15 mg at term. Increase in mass is primarily due to the uptake of maternally derived nutrients by trophotaeniae, externalized embryonic gut derivatives. Trophotaenial development in both species is divisible into five phases. During the first phase, the anus is formed. The second phase involves dilation of the anus, enlargement of the perianal lips, differentiation of the hindgut absorptive epithelium, and formation of the trophotaenial peduncle. The third phase is characterized by a further marked hypertrophy and lateral expansion of the perianal lips that results in the formation of short trophotaenial processes. During the fourth phase, there is continued outward expansion of the inner mucosal surface of the trophotaenial peduncle that results in its eversion and lobulation. Placental function is established by this phase. Axial elongation and dichotomous branching of trophotaenial processes occurs during the fifth phase. Development of rosette and ribbon trophotaeniae differ in the degree of axial elongation during the fifth and final phase.     

Sympodial and monopodial branching inAcer (Aceraceae): Evolutionary trend and ecological implications

The evolutionary trend and its ecological implications in sympodial and monopodial branching patterns has been investigated in 20 JapaneseAcer spp. through comparison of shoot tip abortion and terminal bud formation. The genus is divided into two species groups according to its branching pattern, one (6 species) predominantly exhibiting sympodial branching with frequent monopodial branching in short shoots (sympodial species), and the other (14 species) exhibiting only monopodial branching (monopodial species). The early ontogeny of leaf and bud scales is described. Despite the difference in branching patterns, the bud scales of terminal buds are essentially the same in having a leaf base developed to function as a protecting organ. In all the sympodial species, during the abortion of a sympodium shoot tip, one or two pairs of primordia were found to occur on the apex, and later wither. These primordia resemble bud scales of terminal buds in their ontogeny and morphology, and appear to be rudimentary. It is suggested that a rudimentary terminal bud develops together with the establishment of sympodial branching, and that sympodial branching has originated from monopodial branching. Based on this proposed evolutionary trend, it is suggested thatAcer has moved from less shady habitats into shady habitats with monopodial branching (advantageous for vertical growth) changing into sympodial branching (advantageous for lateral spread).     

Species Diversity and Growth Forms in Tropical American Palm Communities

To advance our understanding of the processes that govern the assembly of palm communities and the local coexistence of numerous palm species, we here synthesize available information in the literature on species diversity and growth-form composition in palm communities across the Americas. American palm communities surveyed had 4–48 (median 16) species in study plots covering 0.09–7.2 ha. Climate, soils, hydrology, and topography are the main factors determining palm community species richness. Tropical lowland terra firme rain forests are the most species-rich whereas forests that are inundated or grow on sandy soils or in areas with seasonal climate have much fewer species. Palm communities in the central-western Amazon and in Central America are significantly richer than the average region and those in the Caribbean significantly poorer in species. As for branching, the 789 species of tropical American palms belong to Corner’s model (solitary, 268 species, 33%), Tomlinsons model (cespitose, 521 species, 66%) and Schoute’s model (dichotomous branching, three species, <1%). We assigned the species to eight different growth forms: (i) Large tall-stemmed Palms (102 spp), (ii) Large-leaved medium–short-stemmed Palms (31 spp), (iii) Medium-sized Palms (95 spp), (iv) Medium/Small Palms with Stout Stem (42 spp), (v) Small Palms (423 spp), (vi) Large acaulescent Palms (28 spp), (vii) Small acaulescent Palms (56 spp), and (viii) Climbing Palms (12 spp). The eight growth forms are differently represented in the palm communities, and the categories Small Palms and Large tall-stemmed Palms dominate the communities both in terms of species richness and in number of individuals.     

Two early mississippian seeds from the price formation of Southwestern Virginia

Lagenospermum imparirameum Arnold, originally described from a few specimens of cupulate seeds borne on two or three times dichotomous branches, is now shown to be borne on more complex branching systems. Details of the cupule and seed morphology are added and an emended diagnosis of the taxon is given. A new species,Gnetopsis hispida, is described as the third occurrence of this genus and the first occurrence in beds of Lower Mississippian Age in North America. The classification, evolutionary implications, and dispersal biology are discussed for each of the seeds     

A new species of <Emphasis Type="Italic">Rhodospatha</Emphasis> (Araceae), with a key to species from the Atlantic Rainforest,Brazil

A new species of Araceae, Rhodospatha arborescens, was found in two preservation areas in Minas Gerais state, Brazil, Caratinga Biological Station and Rio Doce State Park, both located in a semideciduous seasonal forest (Interior Atlantic Rainforest). The new species is helophytic and arborescent. It is described, illustrated, and compared with Rhodospatha species that occur in the Atlantic Rainforest, using a dichotomous key. Information is also presented on the geographic distribution, ecology, and phenology these species.     

A new euphyllophyte Kunia venusta gen. et sp. nov. from the Middle Devonian of Yunnan,South China

Abstract Kunia venusta gen. et sp. nov. is reported from the late Middle Devonian (Givetian) Haikou Formation near Kunming City, Yunnan Province, China. This plant has three orders of naked axes that divide pseudomonopodially. The second‐ and third‐order axes occur in a helix. Fertile appendages are distantly spaced and helically inserted to the third‐order axis; they comprise equally dichotomous branches terminated by two clusters of paired and fusiform sporangia. Sterile appendages are dichotomous and distally recurved. A comparison is made with the basal euphyllophytes including the trimerophytes, cladoxylopsids, zygopterids, stauropterids, and some relevant genera of uncertain affinity. The new plant resembles them in dichotomous appendages with terminal elongated sporangia, but differs mainly in the three orders of pseudomonopodial axes bearing helical laterals. It is thus placed in the Euphyllophytina as incertae sedis. It is suggested that an evolutionary divergence in the branching pattern and appendage morphology might have occurred in the Middle Devonian euphyllophytes, that is, maintaining three dimensions versus yielding more or less planation.     

BATRACHOSPERMUM HETEROCORTICUM SP. NOV. AND POLYSIPHONIA SUBTILISSIMA (RHODOPHYTA) FROM FLORIDA SPRING-FED STREAMS1

Polysiphonia subtilissima Mont. Is reported for the first time from a freshwater environment. The presence of four pericentral cells, subdichotomous branching, apical trichoblasts and rhizoids arising from pericentral cells combined with a lack of cortication and reproductive cells is consistent with marine populations of this species. The range of filament length is 1.4–4.7 cm. Branch diameters are 38–76 μm and pericentral cell lengths are 58–125 μm. Batrachospermum heterocorticum sp. nov. is distinguished primarily by a developmental change in cortical filaments from typical cylindrical cells (5.0–7.9 μm diam in initial stages to enlarged, elliptical cells (12.9–24.1 μm diam) in mature axes. Another unique feature of this species is carpogonia with cylindrical, pedicellate trichogynes on stringht carpogonial branches in mid to outer portions of lateral whorls. Other characteristics of B. heterocorticum include the following: olive-green color, 2–6 cm length, dichotomous to trichotomous fascicles in 4–7 tiers, 385–647 μm whorl diameters, 109–198 μm carpospore diameters and relatively small “chantransia” filaments.     

Interspecific patterns underlying variations in allometric relationship of sympatric Sterculiaceae species in a Bornean rainforest

We compared aboveground tree forms among closely related species in two genera of the Sterculiaceae (Scaphium and Heritiera) in a Bornean mixed dipterocarp forest. Two significant allometric patterns were detected: a negative correlation between the height at the onset of branching and the slope of the species-specific Cr (crown width)-D (stem diameter) allometric relationship for juveniles (D<10 cm), and a negative correlation between H _max (observed maximum height) and the Cr-D slope. The slope of the Cr-D allometric relationship of branched trees was significantly steeper than that of monoaxial (unbranched) trees in most species. These results suggest that the branching growth habit is better adapted than the monoaxial growth habit to crown expansion, and that the morphology of short species is better adapted to crown expansion than that of tall species. We did not detected significant correlations between the height at the onset of branching and the slope of the H (height)-D allometric relationship for juvenile trees, and between H _max and the H-D slope. In addition, the monoaxial and branched juvenile of most species did not differ significantly in the allometric slopes of the H-D relationship. Therefore, the study does not support the hypotheses that a monoaxial growth habit favors rapid height growth and that tall species have allometries better adapted to height growth.     

华北山地6个外生菌根树种的根属性及其与菌根侵染率的关系

该研究以共存于同一暖温带森林的6个外生菌根(ECM)树种为研究对象,测定分析不同根序(1～5级)和功能根系(吸收细根和运输细根)的主要形态和构型属性及ECM侵染率,探究不同外生菌根树种的根属性变异模式及其与菌根真菌侵染程度的关系。结果表明:(1)随着根序的增加,不同树种根直径和单根长度均增加,而比根长和根分支强度均降低;根属性在同一根序下均存在显著的种间差异,尤其是2个裸子植物(落叶松和油松)的根直径较其他4个被子植物大。(2)同一树种的所有根属性在吸收细根和运输细根之间均有显著差异;吸收细根和运输细根的根直径、比根长和根组织密度在树种间均存在显著差异,而其单根长度和根分支强度在树种间无显著差异。(3)ECM侵染率以落叶松最高,千金榆和白桦最低,且与根尖直径呈显著正相关关系,与根尖比根长呈显著负相关关系。研究发现,基于根序或者功能根系,根属性在种间的变异模式不完全一致,单根长度和根分支强度在两个功能根系中均没有表现出显著的种间差异;吸收细根的比根长和根分支强度的变异系数较大,对环境变化有较敏感的响应;古老树种的根直径相对较粗,对菌根真菌的依赖性更高。     

Fine root architecture, morphology, and biomass of different branch orders of two Chinese temperate tree species

We have limited understanding of architecture and morphology of fine root systems in large woody trees. This study investigated architecture, morphology, and biomass of different fine root branch orders of two temperate tree species from Northeastern China—Larix gmelinii Rupr and Fraxinus mandshurica Rupr —by sampling up to five fine root branch orders three times during the 2003 growing season from two soil depths (i.e., 0–10 and.10–20 cm). Branching ratio (R _b) differed with the level of branching: R _b values from the fifth to the second order of branching were approximately three in both species, but markedly higher for the first two orders of branching, reaching a value of 10.4 for L. gmelinii and 18.6 for F. mandshurica. Fine root diameter, length, SRL and root length density not only had systematic changes with root order, but also varied significantly with season and soil depth. Total biomass per order did not change systematically with branch order. Compared to the second, third and/or fourth order, the first order roots exhibited higher biomass throughout the growing season and soil depths, a pattern related to consistently higher R _b values for the first two orders of branching than the other levels of branching. Moreover, the differences in architecture and morphology across order, season, and soil depth between the two species were consistent with the morphological disparity between gymnosperms and angiosperms reported previously. The results of this study suggest that root architecture and morphology, especially those of the first order roots, should be important for understanding the complexity and multi-functionality of tree fine roots with respect to root nutrient and water uptake, and fine root dynamics in forest ecosystems.