Botanical Journal of the Linnean Society
ISSN / EISSN : 0024-4074 / 1095-8339
Published by: Oxford University Press (OUP) (10.1093)
Total articles ≅ 4,979
Latest articles in this journal
Published: 14 June 2021
Botanical Journal of the Linnean Society; doi:10.1093/botlinnean/boab032
Factors influencing diversification rates may be of intrinsic (e.g. morphological novelties) or extrinsic (e.g. long-distance dispersal, availability of ecological niches) nature. Growth habit may influence diversification rates because herbaceous plants often have shorter generation times and a more pronounced r reproductive strategy than their woody relatives. We examined life history and habit evolution, wood anatomy and biogeographical history of Apiaceae tribe Apieae in conjunction with diversification rate analysis to explore which factors may have affected clade species richness and to elucidate the constraints on the evolution of secondary woodiness in this group. We demonstrate that diversification rates are similar in morphologically homogeneous and diverse clades and in herbaceous and woody lineages. The only clade with a significantly elevated diversification rate is Southern Hemisphere Apium, in which diversity probably resulted from several long-distance dispersal events. We also show that wood anatomy in herbaceous and woody species does not differ considerably regardless of their continental or insular origin, but it is affected by stem architecture and plant reproductive strategy. As the taxonomy of Apieae suffers from inflation with numerous monotypic genera, we propose to include Canaria in Rutheopsis, and Foeniculum, Schoenoselinum, Ridolfia and Pseudoridolfia in Anethum.
Published: 14 June 2021
Botanical Journal of the Linnean Society; doi:10.1093/botlinnean/boab034
Faramea is characterized by white or blue, tetramerous corollas and blue-black, fleshy fruits with a single, large pyrene. Both infrageneric relationships and species boundaries are poorly understood in the genus. This study represents the first broad-scale phylogenetic study of Faramea, with 80 of the c. 170 species sampled, 24 by two or more specimens. We aimed to include specimens representing the entire geographical, morphological and ecological ranges of the genus. Morphological characters historically utilized to delimit infrageneric sections in Faramea (e.g. bract and pyrene forms) were also evaluated. Only one of the currently accepted infrageneric sections was recovered as monophyletic (within a complex of species from other sections) and none of the morphological features traditionally utilized to determine infrageneric relationships in the genus was found to be uniquely diagnostic of a larger clade. Some Faramea lineages appear to be geographically isolated, with several clades containing solely specimens collected in the Atlantic Forest biomes. Of the 24 species represented by at least two specimens, 11 were supported as monophyletic, ten as non-monophyletic and three were not resolved as either monophyletic nor non-monophyletic. The results of the present study constitute a good basis for future studies of taxonomy, biogeography and ecology of Faramea.
Published: 14 June 2021
Botanical Journal of the Linnean Society; doi:10.1093/botlinnean/boab035
Recent radiations provide excellent models to gain more insights into evolution, speciation and adaptation. To this end, a well-resolved phylogenetic tree is needed. However, resolving phylogenetic relationships within recent radiations has been difficult as traditional phylogenetic markers failed to provide enough information. We here use plastome data to test their capacity in resolving phylogenetic relationships among a recent rapidly diverging group, Rhodiola, on the Qinghai-Tibetan Plateau. We reconstructed a robust phylogenetic backbone of Rhodiola using 23 plastomes representing all subgenera and sections in previous taxonomic treatments. Based on the backbone, we inferred the spatio-temporal pattern of diversification of the genus. We also traced evolution of five important morphological characters of Rhodiola, including sexual system, inflorescence type and flowering stem, based on the maximum likelihood and the threshold models. Two well-supported clades were revealed in Rhodiola, and the two clades were distinguished by sexual system: species in clade I are mostly hermaphrodite (except R. stapfii and R. integrifolia), and those in clade II are all dioecious. Biogeographic analysis showed that Rhodiola probably originated in the Qinghai-Tibetan Plateau and the Hengduan Mountains. The two major clades diverged c. 6.34 Mya, corresponding to a period of rapid uplift of the Hengduan Mountains and intensification of the Asian monsoon. Character evolution analysis confirmed parallel evolution of dioecy and other adaptive traits, such as marcescent flowering stems, in the genus. We demonstrate that plastome data could significantly improve phylogenetic resolution in plant groups resulting from recent radiations. Our results not only shed new light on the evolutionary history of Rhodiola, but also indicate that more plastome data should be used in resolving phylogenetic relationship in plant groups that have undergone recent radiations.
Botanical Journal of the Linnean Society; doi:10.1093/botlinnean/boab030
Some tree species have distributions on both sides of the Strait of Gibraltar and the Strait of Sicily. It is a challenge to determine whether such distributions result from the Tertiary or Pleistocene or from more recent dispersal related to human activities. Tetraclinis articulata (Cupressaceae) is a gymnosperm that offers an ideal model to deal with this problem because it has a limited area of distribution and has been used only moderately by humans. Three hundred and twenty-three individuals from 30 populations covering the entire distribution of the species were analysed. A multiple approach was developed: (1) by assessing the genetic structure through two molecular techniques, AFLP and nSSR markers, which were used to evaluate the genetic diversity of these populations and the relationships among them and (2) by estimating past distributions. Four lineages of populations that are geographically intermixed to a certain extent are documented here. Results obtained are discussed in the context of palaeontological records and climatic models. There is evidence of an ancient widespread distribution, including Europe, and the subsequent appearance of four isolated lineages that, nowadays, are partially intermixed. Nevertheless, the origin of the current populations could not be fully ascertained through this work, although logical deductions are discussed that consider human activities or, much less probably, wind dispersal of seeds out of refugia in northern Africa-southern Europe during the Quaternary, including shore connections.
Botanical Journal of the Linnean Society; doi:10.1093/botlinnean/boab038
We analysed gynostemium development and morphology of 13 species of Spiranthinae to understand the structure and homology of this organ. Flowers and flower buds in different developmental stages were examined with scanning electron and light microscopy. Gynostemium ontogeny is similar in the early stages among the analysed species, and most of the differences arose at later developmental stages. Gynostemium development starts with the appearance of the anther primordium, followed by the median carpel and finally by the lateral carpel apices. The last emerges as two congenitally united, crescent-shaped prominences located between the median carpel apex and the labellum, eventually forming a rim of tissue on the proximal margin of the stigma. The rim can be receptive or not. The base of the median carpel apex contributes mostly to the receptive stigmatic zone and its apical region develops into the viscidium. The entrance of the stylar canal is located between the two partially non-receptive lateral carpel apices and the receptive base of the median carpel apex, refuting the idea that in Sarcoglottis it is located above the stigmatic area. There are no staminodal primordia, and the membranaceous appendages at each side of the column apex represent extensions of the clinandrium margins.
Botanical Journal of the Linnean Society; doi:10.1093/botlinnean/boab031
The floral anatomy and development of species belonging to all sections of Xyris (Xyris, Nematopus and Pomatoxyris) were investigated comparatively to elucidate gynoecium evolution in the genus, because placentation has been one of the key characters in recognizing its taxonomic sections. In species of section Pomatoxyris (axile placentation), the tricarpellate syncarpous ovary consists of a fertile synascidiate zone, whereas the symplicate zone is fertile only in its lower portion. In species of section Xyris (parietal placentation), the ovary has a short almost sterile synascidiate zone, whereas the more extensive symplicate zone is fertile. In species of section Nematopus (free-central or basal placentation), there is an extremely short and sterile trilocular, completely septate zone at the ovary base. Such differences are related to different patterns of gynoecium development. The ancestral character state reconstruction of placentation types shows that axile placentation is the most likely ancestral condition in Xyris, from which parietal and free-central placentation were derived by shortening of the septa during the evolution of the genus. Basal placentation evolved from free-central placentation and appeared independently several times in section Nematopus. Because the phylogenetic position of X. ptariana and X. teinosperma (section Nematopus) is unknown, either the axile placentation in these species is a reversal or highlights the need for a revised infrageneric classification.
Botanical Journal of the Linnean Society; doi:10.1093/botlinnean/boab033
Cypripedium subtropicum is the only known winter-green species in the genus Cypripedium, whereas the other nearly 50 species keep their leaves for less than half the year. Life form has an important effect on carbon acquisition and adaptation of plants. However, the physiological mechanism behind it remains unclear. In this study, we investigated vegetative anatomy and photosynthetic performance of C. subtropicum across with its leaf ages. These anatomical and photosynthetic traits were also compared with typical Cypripedium spp. and other members of subfamily Cypripedioideae. The obtained results confirmed that this species exhibited many characters of shade plants, such as thin leaves, extremely low photosynthetic rate and light saturation point and high chlorophyll content. Unlike the strategy adopted by typical Cypripedium spp. that quickly achieve annual carbon gain with a high assimilation rate in a short growing season, C. subtropicum obtains its carbon through a low assimilation rate but a much longer leaf lifespan. The local climate and favourable light condition guaranteed the comparable carbon income in winter to compensate for its low photosynthetic capacity. The long-lived, thin leaves of C. subtropicum, differing from the long-lived, thick leathery leaves in conduplicate-leaved genera, represent a distinct adaptive strategy in subfamily Cypripedioideae. Our findings shed light on the divergent and convergent evolution in slipper orchids, and we hope these findings will contribute to the conservation of such an endangered orchid.
Botanical Journal of the Linnean Society; doi:10.1093/botlinnean/boab028
The jewel orchids (Goodyerinae), named after their often colourful leaves, have a pantropical distribution with a clear Asian centre of diversity. However, the Nearctic and Neotropical America together form a second centre of diversity, with one-third of known species of Goodyerinae. Previously, only a few American samples have been included in phylogenetic studies, and their putatively Asian origins and American divergence times were poorly known. To elucidate these topics, we inferred phylogenetic trees, performed molecular dating and reconstructed biogeographic history using nuclear ribosomal ITS and plastid matK sequences for 34 species of Goodyerinae from the New World and 76 previously published accessions of Cranichideae. Our well-supported phylogenetic topology suggests two independent dispersal events to the New World from the Indomalesian region during the Miocene. The first inferred dispersal of a Neotropical clade diverged c. 11 Mya from their most recent common ancestor (MRCA), comprising three highly supported subclades that do not match the limits of Aspidogyne, Kreodanthus and Microchilus as previously circumscribed. The second dispersal involved a largely Nearctic clade of Goodyera s.l. diverging c. 8.4 Mya from the MRCA and exhibiting a complex biogeographic history with subsequent dispersals between the Nearctic and Indomalesia. The occurrence of these species in gallery forests putatively prevented vicariance events imposed by the expansion of the Chacoan region as previously detected for epiphytic Orchidaceae. Eighty-nine nomenclatural combinations and three new names in Microchilus are proposed.
Botanical Journal of the Linnean Society; doi:10.1093/botlinnean/boab012
Environmental heterogeneity across the landscape can cause lineage divergence and speciation. The Geonoma macrostachys (Arecaceae) species complex has been proposed as a candidate case of ecological speciation in Amazonia due to evidence of habitat partitioning and pre-zygotic reproductive barriers between co-occurring morphotypes at a local scale. In this study, we provide a continent-wide perspective of the divergence patterns in G. macrostachys by integrating data from morphological traits, target sequence capture, climate, soil and reproductive biology. A morphometric analysis revealed four morphogroups, defined by traits related to leaf shape. A coalescence-based phylogenetic analysis did not recover the morphogroups as monophyletic, indicating independent evolution of leaf shape across geographical space. We demonstrate scale-dependent habitat differentiation for two of the morphogroups, in which segregation driven mostly by climate was complete at the regional scale but incomplete at the continental scale. Contrary to previous evidence of reproductive isolation in the form of different pollinators and flowering times between sympatric G. macrostachys forms in Peru and Ecuador, these were not found in Colombia, suggesting reproductive barriers have evolved multiple times across its geographical range. Taken together, our findings suggest that ecological divergence and local adaptation is driving diversification in G. macrostachys, and that hyperdiverse regions such as Amazonia are probable arenas for ecological divergence in sympatry.
Published: 28 April 2021
Botanical Journal of the Linnean Society; doi:10.1093/botlinnean/boab024
The Eocene–Oligocene transition period was marked by one of the most abrupt and severe global environmental changes in the Cenozoic record, and this had a marked influence on the evolution of a number of animal and plant groups and entire ecosystems. This study documents continental palynomorphs recovered from the sedimentary rocks of the Dabaa Formation (Qattara area, North-Western Desert, Egypt) located on the southern shore of the Tethys Ocean and dated as Late Eocene–Early Oligocene. The botanical affinities, (phyto)ecology and distribution of the vegetation during the Eocene–Oligocene of the study area are discussed. The recorded assemblages are well preserved and comprise diverse lineages of algae, spores and pollen. They were identified, illustrated and assigned to 46 families encompassing chlorococcalean algae, lycopods, ferns, gymnosperms and angiosperms. The studied assemblages demonstrate the development of tropical vegetation, including tropical deciduous forest, grassland and (semi-)arid tropical shrubland, in which angiosperms were one of the main representatives; additionally open, drier habitats might have existed in the hinterland. Our data have been combined with previous megafossil and palynological evidence to assess and refine vegetation changes during the Early Oligocene time window in Egypt and across North Africa. Vegetation was a mosaic of different vegetation belts that ran more-or-less parallel to the coastline of the Tethys Ocean under the variable geographical influence of lagoons and streams. It is assumed that the belt of tropical forest along the coast of the Tethys Ocean narrowed during the Oligocene in parallel to climatic deterioration following the Eocene–Oligocene boundary, which may have also led to the fractionation of forest habitats.