Hideaki Ohba

Phylogenetic relationships inCrossostylis (Rhizophoraceae) inferred from restriction site variation of chloroplast DNA

Phylogenetic relationships among the nine species ofCrossostylis (Rhizophoraceae) were elucidated using cladistic analysis of restriction site variations of chloroplast DNA. As a result, this genus was found to comprise two pronounced monophyletic groups as follows:C. biflora, C. grandiflora, C. multiflora andC. sebertii; andC. cominsii, C. pachyantha, C. parksii, C. richii andC. seemannii. Moreover, the monophyly ofC. biflora, C. grandiflora andC. sebertii in the former group and the monophyly ofC. pachyantha, C. parksii, C. richii andC. seemannii in the latter group were also suggested. The molecular tree corresponded well with that inferred from morphological data and no discrepancy was recognized. Many of the floral morphological characters reflected lineage, but all seed coat characters were homoplasious. Evolutionary trends in some morphological characters were optimized on the cpDNA tree obtained. Species from New Caledonia and Polynesia were monophyletic, as were those from the Solomon Islands, Vanuatu and the Fiji Islands. All species endemic to the Fiji Islands made a cluster, and this suggests that speciation occurred from a single ancestral species on the Islands.

Is photosynthesis suppressed at higher elevations due to low CO2 pressure

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Chloroplast DNA phylogeny of subtribe Dendrobiinae (Orchidaceae): Insights from a combined analysis based onrbcL sequences and restriction site variation

Phylogenetic analyses using two chloroplast DNA data sets, derived from variation of the ribulose-bisphosphate carboxylase gene (rbcL) and restriction sites, were performed to examine relationships among 13 taxa in subtribe Dendrobiinae, one of the most taxonomically complicated groups in Orchidaceae, and its putative sister groups. Owing to a limited number of informative substitutions, therbcL data set did not provide conclusive evidence in itself. The data set combiningrbcL and restriction site mutations, however, provided the following insights: (1)Pseuderia belongs with tribe Podochileae rather than tribe Dendrobieae. (2) Subtribe Dendrobiinae is monophyletic ifPseuderia is excluded. (3) ExcludingPseuderia, Dendrobiinae comprises three major clades: Clade 1 (Dendrobium sectionSpatulata, Cadetia, Diplocaulobium, andFlickingeria); Clade 2 (Dendrobium sectionsDendrobium andCallista); and Clade 3 (Epigeneium). (4)Epigeneium diverged early from the lineage including Clades 1 and 2. (5) Relative toCadetia, Diplocaulobium, andFlickingeria, Dendrobium is shown to be para-/polyphyletic. (6)Diplocaulobium andFlickingeria constitute a monophyletic clade, from which cladeDendrobium sectionSpatulata andCadetia form succesive sister groups. Among these results, (1) and (5) are especially stable in view of the congruence between the separate and combined analyses as well as robust internal support.

Photosynthetic characteristics of a giant alpine plant, Rheum nobile Hook. f. et Thoms. and of some other alpine species measured at 4300 m, in the Eastern Himalaya, Nepal

The photosynthetic characteristics of a giant alpine plant, Rheum nobile Hook. f. et Thoms. and of some other alpine species were studied in situ at 4300 m, in the Eastern Himalaya, Nepal, during the summer monsoon season. Although rainy and overcast weather was predominant, the daytime photon flux density (400–700 nm) ranged from 300 to 500 μmol quanta m-2 s-1. Under such conditions, the temperature of leaves of R. nobile ranged from 10 to 14°C, and the rate of photosynthetic CO2 exchange ranged from 10 to 16 μmol CO2 m-2 s-1. The ratios of the maximum rate of photosynthetic CO2 fixation to leaf nitrogen content (defined as instantaneous nitrogen-use efficiency, NUE) for the Himalayan forbs that were examined in situ were similar to the NUE values reported for lowland herbaceous species examined under lowland conditions. In contrast to the common belief, theoretical calculations indicate that the decrease in the rate of photosynthesis due to low atmospheric pressure is small. These Himalayan forbs appeared to overcome this small disadvantage by increasing stomatal conductance. Suppression of photosynthesis caused by blockage of stomata by raindrops appeared to be avoided by either of two mechanisms: plants had large hypostomatous leaves that expanded horizontally or they had obliquely oriented amphistomatous leaves without bundle sheath extensions. All these observations indicate that the gas-exchange characteristics of alpine forbs in the Eastern Himalaya are adapted to the local wet and humid monsoon conditions and thus photosynthetic rates attained during the monsoon period are similar to those of lowland plants.

Ecological wood anatomy of NepaleseRhododendron (Ericaceae). 1. Interspecific variation

The relationship of selected wood anatomical characters of NepaleseRhododendron with stem diameter, plant height, altitude, and plant form was investigated. We studied one to three specimens each of 26 species: five species each of trees and subtrees I, three species of subtrees II, and 13 species of shrubs. Multiple regression analysis and actual distribution of character values show that pore characters and multiseriate ray ratio have a stronger correlation with stem diameter than altitude; that pore density, vessel element length, fiber-tracheid length, and multiseriate ray density and width are equally related to altitude and stem diameter, or to altitude and plant height; and that bar number, and multiseriate ray area and height have a stronger connection with altitude. Among the characters, average pore area is most strongly correlated with stem diameter and increases exponentially as diameter increases. For wood structure of NepaleseRhododendron, 17 to 63 % of the variation is affected by non-anatomical factors. The general trends in wood structure of NepaleseRhododendron show that trees and subtrees form one continuous unit whereas shrubs form another that often has wider ranges of variation.

Floral development and phyllotactic variation in Ceratophyllum demersum (Ceratophyllaceae).

The floral development of staminate and pistillate flowers of Ceratophyllum demersum was observed, with particular focus on the phyllotactic variation in staminate flowers, using scanning electronic microscopy (SEM). We discerned patterns of development of some important new morphological features, e.g., the difference and discontinuity between the organ initiation in stamens and that in bracts (or tepals) and the initial presence of a mucilaginous appendage on each pistil. Female flowers are considered to be very specialized through reduction. In male flowers stamen initiation changes between early and late floral development. The four or five stamens in the outermost whorl initiate first on the abaxial and lateral sides of the floral apex and only later on the adaxial side (unidirectional). Later the inner stamens initiate spirally, and this is the main pattern in the stamen initiation. Members of each whorl differ among themselves in time of initiation and in ultimate size. The phyllotactic variation in staminate flowers of Ceratophyllum, suggested by previous studies, is derived from the variation in stamen number and the difference of stamen initiation between the early and later stages. The development in Ceratophyllum has some similarities to those of ANITA plants except for Nymphaeales.

Insight into the basis of root growth in Arabidopsis thaliana provided by a simple mathematical model.

Plant organ growth changes under genetic and environmental influences can be observed as altered cell proliferation and volume growth. The two aspects are mutually dependent and intricately related. For comprehensive growth analysis, it is necessary to specify the relationship quantitatively. Here, we develop a simple mathematical model for this purpose. Our model assumes that the biological activity of a given organ is proportional to the cell number of the organ and is allocated into three aspects: cell proliferation, volume growth, and organ maintenance. We analyzed the growth of primary roots of Arabidopsis thaliana (L.) Heynh. in one tetraploid and four diploid strains using this model. The analysis determined various growth parameters, such as specific cost coefficients of cell proliferation and volume growth for each strain. The results provide insight into the basis of interstrain variations and ploidy effects in root growth.

Floral morphology and phylogenetic analysis inCrossostylis (Rhizophoraceae)

Floral morphology in all ten species ofCrossostylis, one of the inland genera of Rhizophoraceae and is distributed in the South Pacific Islands, was studied to increase our knowledge on floral features of individual species as well as on relationships among the species. Flowers ofCrossostylis, unlike those of the other Rhizophoraceae, always have semi-inferior ovaries and entire petals, but are diversified concerning the number and arrangement of stamens and carpels, the presence or absence of staminodia, sexuality and the structure of nectaries. Despite some doubt of the presence of apomorphies restricted to the whole genus, we tentatively definedCrossostylis by a combination of the presence of the semi-inferior ovary, entire petals, and arillate seeds, and then performed cladistic analysis on the basis of 24 floral and other morphological characters and withCarallia andGynotroches as outgroups. Our phylogenetic analysis suggested that the species ofCrossostylis are divided into two monophyletic groups: one comprising six species distributed in the Solomon Islands, Vanuatu and the Fiji Islands, and the other comprising four species distributed in New Caledonia and Polynesia.

The taxonomic status ofSedum telephium and its allied species (Crassulaceae)

The taxonomic status ofSedum Telephium and its allied species (Crassulaceae-Sedoideae) is discussed, and a new genus,Hylotelephium, is recognized. Under the genus, 27 new combinations are proposed and one new species,H. callichromum, from Central Asia is described.

New Taxa, Names, and Combinations in Saxifraga (Saxifragaceae) for the Flora of China

The following new species, new variety, new name, and four new combinations are published for the forthcoming account of Saxifraga L. in the Flora of China, Volume 8: S. epiphylla Gornall & H. Ohba, sp. nov., S. gemmigera Engler var. gemmuligera (Engler) J. T. Pan & Gornall, comb. nov., S. heterotricha Marquand & Airy-Shaw var. anadena (H. Smith) J. T. Pan & Gornall, comb. et stat, nov., S. hypericoides Franchet var. aurantiascens (Engler & Irmscher) J. T. Pan & Gornall, comb. nov., S. hypericoides var. rockii (Mattfeld) J. T. Pan & Gornall, comb. et stat. nov., S. sinomontana J. T. Pan & Gornall, nom. nov., and S. sinomontana var. amabilis H. Smith ex J. T. Pan, var. nov. In addition, the names S. mengtzeana Engler & Irmscher and S. mengtzeana var. cordatifolia Engler & Irmscher are lectotypified here.