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Dioscorea buchananii Benth. subsp. undatiloba vegetative and reproductive morphology A Habit of male plant with axillary inflorescences B Apical part of male inflorescence showing tepal shape and habit and bud shape C Rehydrated male flower with apical part of pedicel showing stamen morphology (NB tepal and stamen habit influenced by specimen preparation) D Fully opened out rehydrated male flower from above showing tepal shape, torus and pistillode E Female flower with ovary at late anthesis, tepals ascending F Female flower with 3 tepals removed showing torus, staminodia and gynoecium G Immature capsule with pedicel, floral bract and persistent tepals at apex H Leaf of KwaZuluNatal form of Dioscorea buchananii Benth. subsp. undatiloba. Scale bar: A, H 3 cm; B 7 mm; C, D, E 5 mm; F 3 mm; G 2 cm. From Breyer in TM 23387 (A), Junod 2182 (B, G), Medley Wood 11673 (C, D) Gerrard & McKen 1617 (E, F) Medley Wood 12969 (H). Drawn by Lucy Smith.
Source publication
The Dioscorea
buchananii complex is shown to comprise three species, one of which is divided into two subspecies, based on morphological data. Two species, Dioscorea
rupicola Kunth and Dioscorea
multiloba Kunth, are endemic or subendemic to South Africa and of widespread occurrence in KwaZulu Natal. They differ markedly from each other in infloresc...
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Researchers and policymakers have called on the South African National Biodiversity Institute (SANBI), in its role as the statutory biodiversity organisation of South Africa, to develop a coordinated and integrated biodiversity informatics hub. While biodiversity information is increasingly available from several providers, there is no platform thr...
Citations
... La gran diversidad morfológica, su naturaleza dioica, el tamaño pequeño de las flores, así como la plasticidad fenotípica en algunas especies de Dioscorea, dificultan su delimitación Raz, 2016). Esto llevó a que se reportaran complejos taxonómicos sin límites específicos, tornándose en un desafío para su sistemática (Couto et al., 2014;Wilkin y Muasya, 2015;Fraga et al., 2019). ...
Background and Aims: The great variability of characters in Dioscorea makes it difficult to define the species, therefore additional studies are necessary to identify them. Dioscorea ayardei, a recently described endemic species from the Sierras de Calilegua (Jujuy, Argentina), differs by the particularity of the androecium of its staminate flowers which consists of a navicular structure with a single anther in the center and three erect dendriform appendages. The aim of this paper was to carry out an ensemble study of its chromosomal and palynological characters that, added to the morphological ones, provide complementary information for its correct delimitation. Methods: The studied material was identified according to the classic methods in taxonomy and deposited in the LIL Herbarium, of the Fundación Miguel Lillo. For study of meiosis, young flower buds were randomly selected, which were fixed in Farmer for 24 hours and preserved in 70° to -4°C ethyl alcohol. For chromosome staining, 2% propionic hematoxylin was used. Fertility of pollen grains was estimated using the Mützing and DAPI techniques. For the pollen morphology description the material was processed according to the conventional techniques of acetolysis and natural pollen; photographs were taken with light microscope (LM) and scanning electron microscope (SEM). Key results: Dioscorea ayardei presented a gametophytic number n=20II. Meiotic behavior was generally regular. The techniques to estimate viability and fertility of the pollen grain revealed a value of 90-93%, respectively. The morphology showed a small (16-24 µm) to medium (25-30 µm) sized disulcate grain with microreticulate tectum. Conclusions: The basic chromosome number for the genus x=10 is reaffirmed. Dioscorea ayardei is a tetraploid with n=20, with normal meiotic behavior consistent with the potential viability of the pollen grain. The exine ornamentation and chromosome number relates with the New World II clade.
... Hills et al. (2018) gave D. hurteri a provisional IUCN conservation status of Vulnerable which would consequently increase the proportion of threatened species of Dioscorea in South Africa. This new species is related to the D. buchananii species complex (summarised in Wilkin and Muasya (2015)) which would suggest that D. hurteri is an Africa clade species, but molecular studies would need to be undertaken to confirm this. ...
... Species richness of Dioscorea is also high in the east of South Africa, throughout KwaZulu-Natal and into Mpumalanga where the distributions of species such as D. multiloba, D. rupicola and D. sylvatica overlap. From georeferencing herbarium specimens, it was found in this study that D. rupicola has a wider distribution than was previously stated in Wilkin and Muasya (2015), with its range now known to extend from Pirie Mission, King William's Town in the Eastern Cape to the Wonderkloof Nature Reserve in Mpumalanga. Through comparisons of the ER, ED and EDGE diversity maps with SR ( Fig. 3) there was congruence in the distribution of these indices. ...
In an era of increasing threat most species of plant still lack an assessment of extinction risk or an understanding of priority for conservation. Evolutionary distinctiveness (ED) has been used in conjunction with extinction risk to prioritise species for conservation. We apply this approach to an economically important group of plants in Africa; South African Dioscorea (yams), focusing on the Africa clade that contains species used mainly medicinally with a distinct evolutionary history. The results of IUCN Red List assessments for these species were used in subsequent EDGE (Evolutionary Distinct and Globally Endangered) analysis. Species distribution models were produced for Africa clade species using MaxEnt, which were then combined together with the EDGE scores to produce species richness (SR), extinction risk (ER), ED and EDGE diversity maps. Five out of the 15 South African Dioscorea species (all nested in the Africa clade) were found to be in a Red List threat category, and this category was shown to be the main determinant of its EDGE ranking. The spatial distribution of SR, ER, ED and EDGE were compared, and we use these maps to prioritise important areas for conservation in South Africa with hotspots identified as priorities for future conservation of Africa clade Dioscorea.
... minute dioecious flowers and notorious phenotypic plasticity (Raz 2016). Consequently, many taxonomic complexes and assemblages are reported for the genus (Wilkin & Muasya 2015). ...
Based on reproductive characters, two taxa are segregated from D. triangularis (Griseb.) R. Knuth: D. piperifolia var. triangularis and D. galiiflora, the latter previously known only by its type collection. Dioscorea galiiflora is here described, new occurrences are reported and its conservation status is assessed. We also provide nomenclatural notes and circumscribe D. piperifolia var. triangularis, D. galiiflora and D. moyobambensis.
... One of these is the first Dioscorea clade to be studied here via a species level phylogeny, the Africa clade of Viruel et al. [7]. It is also the only clade to have diversified exclusively in Africa and comprises 13 species, as listed in [1] with minor taxonomic changes made in [8]. Nine are South African (sub)endemic species, two extend from South Africa into southern tropical Africa (D. buchananii Benth. ...
... Representatives of all known African perennial-tubered Dioscorea (Dioscoreaceae) were sampled (Table 1). These included five pachycaul species, three Cape species, three species of the D. buchananii subclade (as defined by Wilkin and Muasya [8]), two species of the southern African members of the CL clade, and two species from the Enantiophyllum clade as well as two species from the East Africa subclade. We also included representatives from all known Dioscorea lineages [6]: four from the Mediterranean clade, D. tentaculigera and D. prazeri from South-East Asia and two New World taxa (D. brachybotrya and D. galeottiana), respectively belonging to the New World I (NWI) and II clades (NWII); and Tacca and Stenomeris (Dioscoreaceae) were selected as outgroups. ...
... The only significant variation in floral form is found in D. rupicola, which has only 3 stamens and a discoid torus (as opposed to 6 and a thin, bowl-shaped torus); it also has narrower tepals than those in D. buchananii or D. multiloba and the flower is held pendent. However, these changes are probably linked to the shift to a different pollinator within the forest biome in which this species, principally found the Drakensberg and high elevations in the Eastern Cape [8]. ...
Background
Dioscorea is a widely distributed and highly diversified genus in tropical regions where it is represented by ten main clades, one of which diversified exclusively in Africa. In southern Africa it is characterised by a distinct group of species with a pachycaul or “elephant’s foot” structure that is partially to fully exposed above the substrate. In contrast to African representatives of the genus from other clades, occurring mainly in forest or woodland, the pachycaul taxa and their southern African relatives occur in diverse habitats ranging from woodland to open vegetation. Here we investigate patterns of diversification in the African clade, time of transition from forest to more open habitat, and morphological traits associated with each habitat and evaluate if such transitions have led to modification of reproductive organs and mode of dispersal.
Results
The Africa clade originated in the Oligocene and comprises four subclades. The Dioscorea buchananii subclade (southeastern tropical Africa and South Africa) is sister to the East African subclade, which is respectively sister to the recently evolved sister South African (e. g., Cape and Pachycaul) subclades. The Cape and Pachycaul subclades diversified in the east of the Cape Peninsula in the mid Miocene, in an area with complex geomorphology and climate, where the fynbos, thicket, succulent karoo and forest biomes meet.
Conclusions
Diversification out of forest is associated with major shifts in morphology of the perennial tuber (specifically an increase in size and orientation which presumably led them to become pachycaul) and rotation of stem (from twining to non-twining). The iconic elephant's foot morphology, observed in grasslands and thicket biomes, where its corky bark may offer protection against fire and herbivory, evolved since mid Miocene. A shift in pollination trait is observed within the forest, but entry into open habitat does not show association with reproductive morphology, except in the seed wing, which has switched from winged all round the seed margin to just at the base or at the apex of it, or has been even replaced by an elaiosome.
Electronic supplementary material
The online version of this article (doi:10.1186/s12862-016-0812-z) contains supplementary material, which is available to authorized users.
... The abbreviation "herb. Luc." refers to the private collection of A.F. Lucae, deposited in KIEL (Wilkin & Muasya 2015). See also D. cephalocarpa for elaboration on the Wright 1712 problem. ...
A synopsis of the West Indian Dioscoreaceae is presented. The genus Rajania L. is reduced to a section of Dioscorea L., requiring six new names, 11 new combinations, and reestablishment of two names. Explanations are provided in cases where mixed specimens or otherwise inadequate type material has led to the historical misapplication of names. Lectotypes are designated for 26 names and updated synonymy is provided for all native members of the West Indian Dioscoreaceae. Of the 121 names cited at species level and below, 26 species, one subspecies and a single variety are recognized.
Morphological character data are used to show that a distinct morphotype of Dioscorea L. from KwaZulu-Natal in South Africa is an undescribed species, related to the D. buchananii Benth. species complex but differing in its inflorescence and floral morphology from all other taxa. It is described as Dioscorea hurteri R. Hills & Wilkin, illustrated and a distribution map and ecological information provided. It is known from four localities, just two of which may be protected, within a heavily developed region of South Africa and with an extent of occurrence (EOO) of 9,872 km². Thus, its provisional IUCN conservation status is vulnerable (VU).
