A new species of Polemanniopsis (Apiaceae) from Namibia

A new species of woody Apiaceae, Polemanniopsis namibensis B-E. Van Wyk, A. Burke & C. Mannheimer, is described. The species is allied to Polemanniopsis marlothii but differs in the much smaller habit of (up to 0.6 m vs 1.5–4 m in Polemanniopsis marlothii), the white or greyish colour of the twigs (brown in Polemanniopsis marlothii), the 3-foliolate leaves (predominantly 5-foliate in Polemanniopsis marlothii), the smaller inflorescences with persistent involucral bracts (caducous in Polemanniopsis marlothii) and anatomical details of the leaves. The species is endemic to Namibia and is known only from a localised area in the southern Namib desert near Lüderitz, where it is relatively common.     

Systematic and phylogenetic value of wood anatomy in Heteromorpheae (Apiaceae,Apioideae)

The wood anatomy of all four woody genera of the tribe Heteromorpheae (Apiaceae, subfamily Apioideae) has been described and compared, based on 40 wood samples (representing nine species of Anginon, one species of Glia, three species of Heteromorpha and two species of Polemannia). The four genera were found to be relatively similar in their wood anatomy. Helical thickenings on the vessel walls occur in all species investigated and appear to represent an ancestral character state and a symplesiomorphy for the tribes Bupleurieae and Heteromorpheae. Each of four genera has a diagnostically different combination of character states relating to the diameter of vessels, size of intervessel pits, length of fibres, presence and arrangement of banded axial parenchyma, size of rays and ray cells, and presence of septate fibres and crystals in the ray cells. The occurrence of marginal axial parenchyma in Anginon and Glia may be an additional synapomorphy for these taxa. Variation in the wood anatomy of 31 samples from nine species of Anginon is not correlated with habitat (Fynbos or Succulent Karoo Biomes), but instead appears to reflect adaptations to seasonal aridity found in both ecosystems. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158 , 569–583.     

Size structure and dynamics of some woody perennials along elevation gradient in Wadi Gimal, Red Sea coast of Egypt

The population structure of 10 common woody perennials was investigated in terms of size distribution, height, diameter and density in Wadi Gimal along the Red Sea coast of Egypt. It was attempted to assess the effect of elevation on the size, distribution and density of the studied species. These species are: five trees (Acacia tortilis subsp. raddiana, Acacia tortilis subsp. tortilis, Balanites aegyptiaca, Tamarix aphylla, and Tamarix nilotica), two shrubs (Leptadenia pyrotechnica and Nitraria retusa) and three shrublets (Pulicaria undulata, Zilla spinosa, and Zygophyllum coccineum). The size estimations were then used to classify population into six size classes: 20-80 cm for shrublets, 100-500 cm for shrubs, and 2-10 m for trees. The absolute and relative frequency of individuals and mean height, diameter and height to diameter ratio per individual in each size class were determined. Density of occurrence of most species, except B. aegyptiaca, decreased as elevation increased. The height-to-diameter ratio was less than unity for most of the recorded species except T. nilotica. Several forms - including, positively and negatively skewed, inverse J-shaped, bell shaped and more or less J-shaped distributions - were recognized along the different elevations. The size structure of some species was positively related with soil variables, such as T. nilotica with sulphate, while some others were negatively significant related to the substrate characteristics, such as Z. spinosa with salinity.     

Seasonal dynamics of non-structural carbohydrates in two species of mediterranean sub-shrubs with different leaf phenology

The seasonal dynamics of non-structural carbohydrates in the woody organs of two co-existing mediterranean sub-shrubs were analyzed. The two species show different leaf phenology during summer: Linum suffruticosum, maintains many of its green leaves, while Lepidium subulatum sheds most of its leaves. These different leaf phenologies are related to different strategies with regard to summer stress. The maintenance of leaves in Linum is related to its stress tolerance while Lepidium avoids stress by shedding its leaves. The main objectives were to: (1) determine the differences in the seasonal dynamics of non-structural carbohydrates among the main woody organs of both species; (2) verify if differences in the leaf phenology, and hence in the strategy with regard to summer drought, lead to different seasonal patterns of carbohydrate storage and use between the two species; (3) compare the seasonal dynamics of carbohydrates of the two studied sub-shrubs with those of mediterranean trees and shrubs previously reported in the literature. The concentration of soluble sugars (SS), starch and total non-structural carbohydrates (TNC) were assessed monthly, over 17 months, in the main roots, stems and the transition zone between root and shoot systems of both species. Starch storage capacity and SS, starch and TNC pools were calculated. The seasonal pattern of carbohydrate accumulation was similar among the woody organs analyzed, but it differed with those reported for mediterranean trees and shrubs. The two species showed different pools and seasonal patterns of non-structural carbohydrate concentrations in its woody organ, which corresponded to their different extent of leaf shedding. The stress-avoider Lepidium accumulated starch during spring shoot growth as a carbon store for summer respiration and had low pools of SS, whereas the stress-tolerant Linum increased SS during summer drought to maintain photosynthetic activity during summer and had low starch pools and storage capacity. However, irrespective of their different leaf shedding patterns, both species had a similar relative variation of their TNC concentration, which contrasts with previous results on deciduous and evergreen woody species.     

Variability in water use efficiency at the leaf level among Mediterranean plants with different growth forms

Assessing natural variability of leaf water use efficiency in plants adapted to extreme conditions of the Mediterranean climate represents an important step in the evaluation of the usefulness of some plant ecophysiological traits under water stress. Eleven Mediterranean species naturally inhabiting the Balearic Islands and corresponding to different growth forms (herbs, semi-deciduous shrubs, woody evergreen shrubs and woody evergreen semi-shrubs) were subject to progressive soil water depletion. Leaf intrinsic water use efficiency was measured by gas exchange at four different degrees of water stress. Under well watered conditions, differences in leaf intrinsic water use efficiency (A _N/g _s) among growth forms were limited to woody evergreen semi-shrubs, which presented the highest values. Under water stress conditions, differences became more evident, with a trend for an increase in A _N/g _s from woody evergreen shrubs, through semi-deciduous shrubs and herbaceous to woody evergreen semi-shrubs. The observed variation in A _N/g _s correlated with several physiological (leaf water potential, soil to leaf hydraulic conductance and stomatal conductance) and morphological (stomatal density) parameters, displaying a general relationship for all growth forms. This suggests that the capacity for withstanding water limitation is adaptive for all Mediterranean species. However, when A _N/g _s was related to leaf mass area, this relationship was not generally applicable, and depended on growth forms, suggesting that different growth forms display specific morphological adjustments in response to water shortage.     

Myxobacteria (Myxobacteriales) on leaf surfaces

140 leaf samples were examined, 73 of which (= 52.1%) contained myxobacteria. Three species of the genus Myxococcus, M. virescens, M. fulvus and M. coralloides, could be found more or less frequently in the phyllosphere of woody plants and annuals. Archangium gephyra was observed only once. There was no significant difference in the occurrence of myxobacteria between evergreen leaves and leaves from deciduous trees and shrubs. Fruit-trees yielded the best results.     

Phenology of glucosinolate concentrations in roots,stems and leaves of Cardamine cordifolia

Total concentrations of isothiocyanate-yielding glucosinolates (IYG) were measured in roots, stems, basal leaves and cauline leaves of the herbaceous perennial Cardamine cordifolia (bittercress, Cruciferae), sampled at three sites in the Colorado Rockies during 1981. Significant variation in quantity was partitioned among plant parts, among sampling dates throughout the growing season, and among the three sites. Roots and basal leaves maintained high and similar concentrations of IYG through the season, while cauline leaves and stems showed seasonal declines, associated partly with flowering. Roots also consistently produced oxazolidinethione-yielding glucosinolates (hydroxylated analogues of IYG), whereas above-ground parts were variable for the presence of these compounds. Seasonal and plant-part variability in glucosinolate content and spatial patchiness of glucosinolate phenotypes contribute to the variation in herbivore occurrence and damage documented in previous studies of this native crucifer.     

End of season carbon supply status of woody species near the treeline in western China

As trees and shrubs approach the high elevation tree limit, it is often assumed that they fall short in photosynthate (source limitation). Alternatively, low temperature may restrict carbon investment (growth, sink limitation). The content of mobile non-structural carbohydrates (NSC) in tissues is considered a measure of the carbon source–sink balance. To test the source vs. sink limitation hypothesis, we compared late-season NSC concentrations of various woody taxa across altitudinal gradients from the subalpine forest to the treeline at the eastern edge of the Tibetan Plateau. Since we were interested in the generality of trends, we present “community” trends across four taxa, namely Quercus aquifolioides, Abies faxoniana, Rhododendron fabri subsp. prattii and Sorbus rufopilosa. NSC concentrations increased significantly with altitude in branch wood, current-year and last-year leaves, while there were no significant trends in stem sapwood and root xylem. The sugar to starch ratio was roughly 1:1 in branches and evergreen leaves, while stems and roots showed a higher starch fraction. Analyses of total nitrogen in leaves and wood tissues indicated no change in the trees’ nitrogen supply with elevation. The overall altitudinal trends of NSC in this group of woody plant species revealed no depletion of carbon reserves near the tree limit, suggesting that sink limitation predominates woody plant life across this treeline ecotone community.     

A new species of Ionactis (Asteraceae: Astereae) from Southern Nevada and an overview of the genus

Ionactis caelestis Leary & Nesom is a new species known from a single population that occurs on the Aztec Sandstone near Bridge Mountain in the Spring Mountains of Clark County, Nevada. It is placed in the genus Ionactis (=Aster subg. Ianthe) on the basis of its crowded, multicipital crown, lack of persistent basal leaves and presence of densely arranged cauline ones, strongly carinate phyllaries, blue rays, disc style branches with linear-lanceolate appendages, asymmetric carpopodia, double pappus, and chromosome number of 2n = 9 II. A key to the four species of the genus emphasizes the distinction of the new species in its taproot, the abundant, large, glandular trichomes on its stems and leaves, and disc flowers with sterile ovaries. Ionactis is more similar to the goldenaster (Heterotheca) lineage than to Aster, with which it has been allied formerly. The core of the goldenaster genera differ from Ionactis primarily in their yellow-rayed heads, the crystal complement within cells of their disc corollas, and their primarily multinerved achenes.     

西藏毛茛属二新种

该文描述了发现自中国西藏南部的毛茛科毛茛属二新种,即隆子毛茛(Ranunculus longziensis W.T. Wang)和单根毛茛(R. uniradicatus W. T. Wang)。隆子毛茛(新种)与睫毛毛茛(R. densiciliatus W. T.Wang)在亲缘关系上甚为相近,两者不同的是此新种(隆子毛茛)的茎无毛,叶也无毛,基生叶不分裂,多具5条脉,茎生叶呈披针状条形;单根毛茛(新种)与聂拉木毛茛(R. nyalamensis W. T. Wang)在体态上稍微相似,两者不同的是此新种(单根毛茛)为一年生草本植物,只具一条须根,茎无毛,花瓣呈狭倒卵形,子房被短柔毛。     

Leafing patterns and leaf traits of four evergreen shrubs in the Patagonian Monte, Argentina

We assessed leafing patterns (rate, timing, and duration of leafing) and leaf traits (leaf longevity, leaf mass per area and leaf-chemistry) in four co-occurring evergreen shrubs of the genus Larrea and Chuquiraga (each having two species) in the arid Patagonian Monte of Argentina. We asked whether species with leaves well-defended against water shortage (high LMA, leaf longevity, and lignin concentration, and low N concentration) have lower leaf production, duration of the leafing period, and inter-annual variation of leafing than species with the opposite traits. We observed two distinctive leafing patterns each related to one genus. Chuquiraga species produced new leaves concentrated in a massive short leafing event (5–48 days) while new leaves of Larrea species emerged gradually (128–258 days). Observed leafing patterns were consistent with simultaneous and successive leafing types previously described for woody plants. The peak of leaf production occurred earlier in Chuquiraga species (mid September) than in Larrea species (mid October–late November). Moreover, Chuquiraga species displayed leaves with the longest leaf lifespan, while leaves of Larrea species had the lowest LMA and the highest N and soluble phenolics concentrations. We also observed that only the leaf production of Larrea species increased in humid years. We concluded that co-occurring evergreen species in the Patagonian Monte displayed different leafing patterns, which were associated with some relevant leaf traits acting as plant defenses against water stress and herbivores. Differences in leafing patterns could provide evidence of ecological differentiation among coexisting species of the same life form.     

Potential of Sahelian Native Shrub Materials to Suppress the Spiral Nematode Helicotylenchus dihystera

Pearl millet (Pennisetum glaucum) is a drought-tolerant cereal commonly grown for grain and fodder in arid areas throughout the world. Senegalese millet fields are infested with Helicotylenchus. The native evergreen woody shrub Piliostigma reticulatum is widely distributed in sub-Saharan Africa. Its coppiced residues are used by small farmers as mulch in crop fields. The shrub’s nematicidal effect on the spiral nematode Helicotylenchus dihystera was evaluated in a pearl millet pot experiment. The abundance of nematodes decreased by 64% after application of either leaf powder or a pulverized mixing of leaves and stems, suggesting the use of aboveground materials of P. reticulatum as a potential nematicide. The results show promise for use of a local resource by subsistence farmers in the Sahel. Further research is needed on application to fully develop this approach as a biopesticide.     

Patterns of wood carbon dioxide efflux across a 2,000-m elevation transect in an Andean moist forest

During a 1-year measurement period, we recorded the CO₂ efflux from stems (R _S) and coarse woody roots (R _R) of 13–20 common tree species at three study sites at 1,050, 1,890 and 3,050 m a.s.l. in an Andean moist forest. The objective of this work was to study elevation changes of woody tissue CO₂ efflux and the relationship to climate variation, site characteristics and growth. Furthermore, we aim to provide insights into important respiration–productivity relationships of a little studied tropical vegetation type. We expected R _S and R _R to vary with dry and humid season conditions. We further expected R _S to vary more than R _R due to a more stable soil than air temperature regime. Seasonal variation in woody tissue CO₂ efflux was indeed mainly attributable to stems. At the same time, temperature played only a small role in triggering variations in R _S. At stand level, the ratio of C release (g C m^?2 ground area year^?1) between stems and roots varied from 4:1 at 1,050 m to 1:1 at 3,050 m, indicating the increasing prevalence of root activity at high elevations. The fraction of growth respiration from total respiration varied between 10 (3,050 m) and 14% (1,050 m) for stems and between 5 (1,050 m) and 30% (3,050 m) for roots. Our results show that respiratory activity and hence productivity is not driven by low temperatures towards higher elevations in this tropical montane forest. We suggest that future studies should examine the limitation of carbohydrate supply from leaves as a driver for the changes in respiratory activity with elevation.     

Shoot growth phenology of co-existing evergreen and deciduous species in an oak forest

Shoot growth phenology was compared for the saplings of evergreen and deciduous woody species sharing the same microsite. Growth initiation occurred earlier in evergreens (among co-stratal species) while deciduous species completed their growth earlier. Shoot growth rate was significantly greater (P<0.01) for deciduous trees than evergreen trees. The amount of shoot elongations and shoot diameter was also significantly greater (P<0.01) for deciduous trees than evergreens. On the other hand, among shrubs the amount of shoot elongation and shoot diameter was greater for evergreens but the rate of elongation and diameter was more or less similar for both. The duration of shoot elongation and shoot diameter was significantly longer in evergreens than the deciduous species. Leaf packing (number of leaves per shoot) was significantly more dense in evergreen trees (P<0.01) than in deciduous tree species. Leaf packing was more dense in evergreen than deciduous shrubs but the difference was not significant. Leaf area (per individual leaf) at full expansion was significantly greater (P<0.01) in deciduous species. Leaf dry mass and specific leaf mass in the initial stage was significantly greater for evergreen species than for deciduous species. The number of buds/10 cm of shoot was higher in evergreens. However, the per cent mortality was also higher in them.     

Patterns of nitrogen conservation in shrubs and grasses in the Patagonian Monte,Argentina

We analysed the main plant strategies to conserve nitrogen in the Patagonian Monte. We hypothesized that the two main plant functional groups (xerophytic evergreen shrubs and mesophytic perennial grasses) display different mechanisms of nitrogen conservation related to their structural and functional characteristics. Evergreen shrubs are deep-rooted species, which develop vegetative and reproductive growth from spring to late summer coupled with high temperatures, independently from water inputs. In contrast, perennial grasses are shallow-rooted species with high leaf turnover, which display vegetative growth from autumn to spring and reproductive activity from mid-spring to early-summer, coupled with precipitation inputs. We selected three evergreen shrubs (Larrea divaricata Cav., Atriplex lampa Gill. ex Moq. and Junellia seriphioides (Gilles and Hook.) Moldenke) and three perennial grasses (Stipa tenuis Phil., S. speciosa Trin. and Rupr. and Poa ligularis Nees ex Steud.), characteristic of undisturbed and disturbed areas of the Patagonian Monte. N concentration in expanded green and senesced leaves was estimated in December 1997 (late spring) and June 1998 (late autumn). Deep-rooted evergreen shrubs displayed small differences in N concentration between green and senesced leaves (low N-resorption efficiency), having high N concentration in senesced leaves (low N-resorption proficiency). Shallow-rooted perennial grasses, conversely, showed high N-resorption efficiency and high N-resorption proficiency (large differences in N concentration between green and senesced leaves and very low N concentration in senesced leaves, respectively). The lack of a strong mechanism of N resorption in evergreen shrubs apparently does not agree with their ability to colonize N-poor soils. These results, however, may be explained by lower N requirements in evergreen shrubs resulting from lower growth rates, lower N concentrations in green leaves, and lower leaf turnover as compared with perennial grasses. Long-lasting N-poor green tissues may, therefore, be considered an efficient mechanism to conserve N in evergreen shrubs in contrast with the mechanism of strong N resorption from transient N-rich tissues displayed by perennial grasses. Evergreen shrubs with low N-resorption efficiency provide a more N-rich substrate, with probably higher capability of N mineralization than that of perennial grasses, which may eventually enhance N fertility and N availability in N-poor soils.     

A new species of Combretum section Ciliatipetala (Combretaceae) from southern Africa, with a key to the regional members of the section

Combretum stylesii O.Maurin, Jordaan & A.E.van Wyk, a liana or slender tree with scrambling branches from the Tugela River Valley (KwaZulu-Natal), South Africa, is described. Molecular data supports its placement in subgenus Combretum section Ciliatipetala with its closest relative Combretum edwardsii. The new species differs from C. edwardsii in having, amongst others, a single mature leaf form, leaves softly textured, with whitish hairs, often with drooping habit, shorter leaf petioles (less than 5 mm), and less complex 8-celled leaf scales. A key to the species and infraspecific taxa of section Ciliatipetala in the Flora of southern Africa region is provided.     

Occurrence of endodermis with a casparian strip in stem and leaf

It is well known that an endodermis with casparian strip always occurs in roots, but few people are aware that it also occurs in stems and leaves of some vascular plants. The rather sparse literature on endodermis in aerial organs was last included in a review in 1943. The present compilation, which does not consider hydathodes, nectaries, or other secretory structures, emphasizes distribution of cauline and foliar endodermis with casparian strip. It occurs unevenly among major taxa: quite common in rhizomes and leaves among pteridophyte groups, with exceptions; absent in gymnosperm stems but found in leaves at least among some conifers; in stems of at least 30 mostly herbaceous angiosperm families, but far less common in leaves, where it is mostly reported from petioles. Etiolation can induce casparian strips in stems and petioles of some herbaceous plants, but results from leaf blades are questionable. There are recent reports of an endodermis with casparian strip in leaves of both woody and herbaceous taxa. The physiological function, if any, of a casparian strip in aerial organs remains unknown.     

Comparative protective strategies of Cistus albidus and Quercus ilex facing photoinhibitory winter conditions

The role of structural photoprotection under photoinhibitory winter conditions was evaluated in two Mediterranean woody species: Cistus albidus (semideciduous) and Quercus ilex (evergreen). Shoots were manipulated in order to modify the light load naturally received by the leaves throughout the cold season, and monitored for changes in maximum photochemical efficiency of PSII, phenology, and leaf morphology. Naturally steep leaves of C. albidus were restrained to a horizontal position, and compared with control leaves (naturally horizontal, or steeply inclined). Fully exposed leaves of Q. ilex were artificially protected through partial shading, and compared with control leaves (not shaded). During the cold season, the most exposed (either naturally or artificially) leaves were always more photoinhibited (had lower maximal photochemical efficiency of PSII) than the photoprotected ones. The differences disappeared at the beginning of spring. Winter photoinhibition was not more pronounced in older than in younger leaves of C. albidus, indicating that inclination rather than age affected their photochemical efficiency. Leaf chlorophyll contents were not significantly affected by the manipulations. Leaf thickness decreased slightly in the least exposed shoots of the evergreen species, but no changes were detected in leaf morphological traits of the semideciduous one. The increased photoinhibitory pressure led only to slight and non-significant changes in phenology and growth.     

Oberholzeria (Fabaceae subfam. Faboideae), a New Monotypic Legume Genus from Namibia

Oberholzeria etendekaensis, a succulent biennial or short-lived perennial shrublet is described as a new species, and a new monotypic genus. Discovered in 2012, it is a rare species known only from a single locality in the Kaokoveld Centre of Plant Endemism, north-western Namibia. Phylogenetic analyses of molecular sequence data from the plastid matK gene resolves Oberholzeria as the sister group to the Genisteae clade while data from the nuclear rDNA ITS region showed that it is sister to a clade comprising both the Crotalarieae and Genisteae clades. Morphological characters diagnostic of the new genus include: 1) succulent stems with woody remains; 2) pinnately trifoliolate, fleshy leaves; 3) monadelphous stamens in a sheath that is fused above; 4) dimorphic anthers with five long, basifixed anthers alternating with five short, dorsifixed anthers, and 5) pendent, membranous, one-seeded, laterally flattened, slightly inflated but indehiscent fruits.