Papers by Alexei Oskolski
Bot. Zh, 2009
The anatomical structure of bark, leaves and fruits of Myrica gale and M. tomentosa have been exa... more The anatomical structure of bark, leaves and fruits of Myrica gale and M. tomentosa have been examined. Both species show very similar anatomical structure, but M. gale is distinctive from M. tomentosa by occurrence of small glandules and fewer hairs on the leaf epidermis. Our results confirm specific rank of M. tomentosa. Diagnostic features for identification of the M. gale plant material have been distinguished.
South African Journal of Botany, Mar 1, 2017
fundamental source of income but comes at an expense to the environment. Most plants traded at th... more fundamental source of income but comes at an expense to the environment. Most plants traded at the market are harvested from wild resources resulting in noticeable levels of species depletion. Adulteration, trade using vernacular names and morphological similarities of plants or the lack thereof, makes identifying samples on a taxonomic level challenging. In this study, DNA barcoding was implemented to rapidly identify the plants, more specifically bulbous plants, traded at the Faraday market. Sixty samples were collected and sequenced for the core barcoding regions (rbcLa and matK). BLAST results were ambiguous for rbcLa whereas matK results were more specific, permitting samples to be identified to species level. Overall, 85% of the samples were identified to species level. Two additional approaches, the tree-based and character-based methods were followed to validate matK samples to species level. Results from this study reveal a noticeable increase in the number of species traded with the majority of sought-after species of Least Concern. However, 10% of the species are Declining or Near Threatened in the wild posing a serious conservation issue. Prolonged unsustainable trade of these plants could lead to more Critically Endangered species in the future. An important outcome of the project is a new collaboration with the Department of Environmental Affairs to address these problems. Results and the consequences of illegal trade will be discussed.
South African Journal of Botany, Mar 1, 2018
fundamental source of income but comes at an expense to the environment. Most plants traded at th... more fundamental source of income but comes at an expense to the environment. Most plants traded at the market are harvested from wild resources resulting in noticeable levels of species depletion. Adulteration, trade using vernacular names and morphological similarities of plants or the lack thereof, makes identifying samples on a taxonomic level challenging. In this study, DNA barcoding was implemented to rapidly identify the plants, more specifically bulbous plants, traded at the Faraday market. Sixty samples were collected and sequenced for the core barcoding regions (rbcLa and matK). BLAST results were ambiguous for rbcLa whereas matK results were more specific, permitting samples to be identified to species level. Overall, 85% of the samples were identified to species level. Two additional approaches, the tree-based and character-based methods were followed to validate matK samples to species level. Results from this study reveal a noticeable increase in the number of species traded with the majority of sought-after species of Least Concern. However, 10% of the species are Declining or Near Threatened in the wild posing a serious conservation issue. Prolonged unsustainable trade of these plants could lead to more Critically Endangered species in the future. An important outcome of the project is a new collaboration with the Department of Environmental Affairs to address these problems. Results and the consequences of illegal trade will be discussed.
Iawa Journal, 1995
The wood anatomy of 31 Schefflera species from Indochina, Australia, Oceania, Africa, and South A... more The wood anatomy of 31 Schefflera species from Indochina, Australia, Oceania, Africa, and South America, 3 species of Didymopanax from South America, and Tupidanthus calyptratus and Scheffleropsis hemiepiphytica from Indochina (Araliaceae) are described. Seven groups of species can be recognised. Tupidanthus and Scheffleropsis are very similar to the Schefflera speeies from sections Schefflera (subseetions Octophyllae and Heptapleurum) and Brassaia (subsection Actinophyllae). These taxa have characteristic vessel-ray and vessel-axial parenchyma piuing formed by solitary large pits among numerous distinctly smaller ones. Didymopanax cannot be separated from the South American Schefflera species with respect to wood anatomy. Seetion Agalma of Schefflera differs from other studied taxa by the presence of helical thickenings on the vessel walls. The relationships of the examined species is discussed. The presence of radial canals in Schefflera and allied taxa is regarded as a primitive feature. The mountain species tend to have more distinct growth rings, more numerous and narrower vessels, and wider and (or) higher rays than those in the lowland. Helical thickenings and abundant vascular tracheids are restricted to mountain species. Schefflera digitata from New Zealand, the only temperate Schefflera species, shows these features in the most pronounced form, but lacks helical thickenings. It also has the shortest vessel elements in the genus.
Botanicheskiĭ Zhurnal, 2009
Abstract The anatomical structure of bark, leaves and fruits of Myrica gale and M. tomentosa have... more Abstract The anatomical structure of bark, leaves and fruits of Myrica gale and M. tomentosa have been examined. Both species show very similar anatomical structure, but M. gale is distinctive from M. tomentosa by occurrence of small glandules and fewer hairs on the leaf epidermis. Our results confirm specific rank of M. tomentosa. Diagnostic features for identification of the M. gale plant material have been distinguished.
Botanica Pacifica
Bark structure of Polylepis incana (Sanguisorbeae, Rosaceae) is described and compared with that ... more Bark structure of Polylepis incana (Sanguisorbeae, Rosaceae) is described and compared with that in related genera Cliffortia and Leucosidea. Tribe Sanguisorbeae shows an extraordinary diversity of bark abscission patterns. The outermost bark portions are peeling off along the non-conducting secondary phloem (Leucosidea, Cliffortia ruscifolia), or along the periderm (C. strobilifera). The protective function is performed by phellem (Leucosidea), or by sclerified secondary phloem (Cliffortia). In Polylepis, the separation layers occur in phellem and non-sclerified phloem, while a prominent protective layer is absent: its function is performed by multiple uniseriate layers of suberized phellem cells. Such pattern of peeling bark has not been reported yet elsewhere. Lenticels lack in Polylepis, but its phellem is similar in its structure (probably, also in some functions) to stratified filling lenticular tissue. Smooth surface of Polylepis bark is maintained by permanent abscission of ...
Plants
The bark fulfils several essential functions in vascular plants and yields a wealth of raw materi... more The bark fulfils several essential functions in vascular plants and yields a wealth of raw materials, but the understanding of bark structure and function strongly lags behind our knowledge with respect to other plant tissues. The recent technological advances in sampling and preparation of barks for anatomical studies, along with the establishment of an agreed bark terminology, paved the way for more bark anatomical research. Whilst datasets reveal bark’s taxonomic and functional diversity in various ecosystems, a better understanding of the bark can advance the understanding of plants’ physiological and environmental challenges and solutions. We propose a set of priorities for understanding and further developing bark anatomical studies, including periderm structure in woody plants, phloem phenology, methods in bark anatomy research, bark functional ecology, relationships between bark macroscopic appearance, and its microscopic structure and discuss how to achieve these ambitious ...
National Science Review
Fossil wood of Chinese white pine (Pinus armandii Franch.) from the Late Pleistocene deposits of ... more Fossil wood of Chinese white pine (Pinus armandii Franch.) from the Late Pleistocene deposits of Maoming Basin of South China provides the first megafossil evidence for glacial expansion of the range of a cold-tolerant species in low latitudes.
Journal of Palaeogeography
Fusion between floral organs or their parts is believed to have played key roles in the origin an... more Fusion between floral organs or their parts is believed to have played key roles in the origin and subsequent diversification of angiosperms. Two types of fusion can be recognized: postgenital and congenital. Postgenital fusion is readily observable during flower development: primary morphological surfaces of contacting structures meet and join during this process. After perfect postgenital fusion, no trace of the original epidermal layers can be recognized, but these remain visible, often in modified form, after imperfect postgenital fusion. Congenital fusion cannot be directly observed and takes place due to differential growth. In the case of complete congenital fusion, free parts of fused organs cannot be seen at any developmental stages. Incomplete congenital fusion implies the presence of free organ parts on the common (united) base; it can be divided into early and late congenital fusion depending on whether the common base precedes or follows the initiation of free parts during development. Phenomena related to congenital fusion are the development of free organs from common primordia, hybridization of developmental pathways, loss of organ individuality, heterotopies and fasciation. Differences between congenital and postgenital fusion are much more unequivocal than those between the presence and absence of fusion. There is no abrupt boundary between imperfect postgenital fusion and transient contact between organs during development. Structures assumed to be congenitally fused clearly develop as a unit, but it is necessary to demonstrate that these structures indeed belong to different merged organs (instead of being parts of the same organ or two distinct organs on a common base). This only can be done in the framework of comparative morphology. Analyses of both types of fusion involve arbitrary decisions, so it is not appropriate to discard the existence of any type. Conventional interpretations of morphological concepts lie at the base of analyses of character evolution, even if they are performed using maximum parsimony or model based methods and molecular phylogenetic data. Patterns of organ fusion are discussed here using three case studies.
Asian species of the genus Schefflera represent a monophyletic group well supported by molecular,... more Asian species of the genus Schefflera represent a monophyletic group well supported by molecular, morphological and geographical data. This group, also known as Asian Schefflera Clade, comprises more than 300 species, i.e. about one fourth of the family Araliaceae. The formal infrageneric system of the Asian Schefflera Clade is so far lacking and classifications developed for the regional accounts of the genus Schefflera are out of date. We have performed mapping of nine morphological characters onto our extended molecular phylogenetic tree which comprises 71 species of Asian Schefflera Clade in order to evaluate phylogenetic relationships among the species and to find morphological features which can be used for characterization of infrageneric subgroups of the Clade.
Papers in Palaeontology, 2021
A new species, Tetradium nanningense sp. nov. (Rutaceae), is described on the basis of well‐prese... more A new species, Tetradium nanningense sp. nov. (Rutaceae), is described on the basis of well‐preserved mummified wood from the upper Oligocene Yongning Formation of Nanning Basin, Guangxi Province, South China. This species represents the most ancient fossil evidence of the genus Tetradium in Asia, the region of its modern distribution. Its occurrence in the late Oligocene is consistent with the diversification age of the modern Asian species within this genus as estimated by molecular dating: T. nanningense could be closely related to an ancestor of extant Tetradium species. The fossil record of Tetradium suggests that this genus migrated from North America to eastern Asia in the Oligocene. The presence of (semi‐)ring‐porous wood and helical thickenings on vessel walls in T. nanningense provides new evidence for the independent gains of these traits in the course of evolution among different plant groups from eastern and south‐eastern Asia in the Oligocene. These wood features might...
Botanical Journal of the Linnean Society, 2021
As Proteaceae subfamily Proteoideae are richly represented in the Cape Floristic Region of southe... more As Proteaceae subfamily Proteoideae are richly represented in the Cape Floristic Region of southern Africa and in south-western Australia, it is a convenient group for comparative studies of evolution and adaptation of plants in widely separated areas with a Mediterranean-type climate. Although species of Proteoideae attract considerable attention of researchers, the structural diversity of wood in this group remains under-explored. The wood structure of 51 species of 14 African and Australian genera of Proteoideae (Proteaceae) has been studied. These taxa are uniform in their wood structure; the diversity patterns are more related to plant stature, climatic factors and fire-survival strategies than to the taxonomy or phylogeny of the subfamily. Increases in length and diameter of fibres and diameter of pits in fibre walls are associated with a shift from a semi-arid winter-dry climate to a milder climate with winter rainfall. These trends may imply the transition from non-conductin...
IAWA Journal, 2021
A new species, Syzygium guipingensis sp. nov. (Myrtaceae), is described based on mummified fossil... more A new species, Syzygium guipingensis sp. nov. (Myrtaceae), is described based on mummified fossil wood from the Miocene Erzitang Formation of Guiping Basin, Guangxi, South China. This species represents the most ancient reliable fossil record of the genus Syzygium in eastern Asia, showing the greatest similarity to the extant species S. buxifolium Hook. et Arnott. Its occurrence in the Miocene is consistent with the diversification age of the Asian lineage within Syzygium as estimated by molecular dating (11.4 Ma). The fossil record of Syzygium suggests that this genus migrated from Australia to eastern Asia in the Miocene, coincidently with the formation of island chains between these continents.
Botanical Journal of the Linnean Society, 2021
Pseudomonomerous gynoecia with three (or four) carpels are unknown in the species-rich core group... more Pseudomonomerous gynoecia with three (or four) carpels are unknown in the species-rich core group of Apiales, but this condition is shared by three species-poor families (Pennantiaceae, Torricelliaceae, Griseliniaceae) that form the basal grade of the order. Testing a hypothesis on the ancestral nature of carpel dimorphism in Apiales requires comparative data for all three lineages in this grade. We provide the first detailed description of flowers, including floral vasculature and gynoecium development, in a member of Pennantiaceae (Pennantia corymbosa). In contrast to many other Apiales, the inflorescence of Pennantia is paniculate and therefore has an unstable number of phyllomes in axes terminated by flowers. All phyllomes in the inflorescence are shifted onto lateral branches they subtend exhibiting recaulescence, a pattern that has not been reported elsewhere in Apiales. Plants are dioecious with functionally unisexual flowers. There are normally five stamens alternating with ...
Asymmetry in Plants, 2019
Botanical Journal of the Linnean Society, 2020
Astropanax and Neocussonia are two recently resurrected genera of Araliaceae that had long been c... more Astropanax and Neocussonia are two recently resurrected genera of Araliaceae that had long been considered as an Afro-Malagasy lineage of Schefflera. The wood structure of 11 Neocussonia spp. and eight Astropanax spp. has been studied. Neocussonia shows a higher average length of vessel elements (1319 µm) and number of bars on perforation plates (up to 66) than any other Araliaceae examined to date. Neocussonia is distinct from Astropanax by its smaller diameter and higher frequency of vessels, rare occurrence of simple perforation plates, more numerous bars on scalariform perforation plates and smaller intervessel pits. The interspecific variation in percentage of simple perforation plates, bar number on scalariform perforation plates, vessel frequency and uniseriate ray number is affected by seasonality in temperature and precipitation. The sharp distinction in wood structure between samples of A. abyssinicus from Cameroon and Burundi suggests that the populations from different p...
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Papers by Alexei Oskolski