BackgroundThe picturesque limestone karsts across the Sino-Vietnamese border are renowned biodiversity hotspot, distinguished for extremely high endemism of calciphilous plants restricted to caves and cave-like microhabitats that have functioned as biological refugia on the otherwise harsh habitats. To understand evolutionary mechanisms underlying the splendid limestone flora, dated phylogeny is reconstructed for Asian Begonia, a species-rich genus on limestone substrates represented by no less than 60 species in southern China, using DNA sequences of nrITS and chloroplast rpL16 intron. The sampling includes 94 Begonia species encompassing most major Asian clades with a special emphasized on Chinese species.ResultsExcept for two tuberous deciduous species and a species with upright stems, a majority of Sino-Vietnamese limestone Begonia (SVLB), including sect. Coelocentrum (19 species sampled) and five species of sect. Diploclinium, Leprosae, and Petermannia, are rhizomatous and grouped in a strongly supported and yet internally poorly resolved clade (Clade SVLB), suggesting a single evolutionary origin of the adaptation to limestone substrates by rhizomatous species, subsequent species radiation, and a strong tendency to retain their ancestral niche. Divergence-time estimates indicate a late Miocene diversification of Clade SVLB, coinciding with the onset of the East Asian monsoon and the period of extensive karstification in the area.ConclusionsBased on our phylogenetic study, Begonia sect. Coelocentrum is recircumscribed and expanded to include other members of the Clade SVLB (sect. Diploclinium: B. cavaleriei, B. pulvinifera, and B. wangii; sect. Leprosae: B. cylindrica and B. leprosa; sect. Petermannia: B. sinofloribunda). Because species of Clade SVLB have strong niche conservatism to retain in their ancestral habitats in cave-like microhabitats and Begonia are generally poor dispersers prone to diversify allopatrically, we propose that extensive and continuous karstification of the Sino-Vietnamese limestone region facilitated by the onset of East Asian monsoon since the late Miocene has been the major driving force for species accumulation via geographic isolation in Clade SVLB. Morphologically species of Clade SVLB differ mainly in vegetative traits without apparent adaptive value, suggesting that limestone Begonia radiation is better characterized as non-adaptive, an underappreciated speciation mode crucial for rapid species accumulations in organisms of low vagility and strong niche conservatism.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-55-1) contains supplementary material, which is available to authorized users.

Ludwigia sect. Microcarpium, which consists of 14 species distributed mainly in the southeastern United States, is the second-largest section in the genus, the largest being the phylogenetically central sect. Myrtocarpus of South America.Plants of Ludwigia sect. Microcarpium are morphologically diverse; they form a polyploid complex of four diploids, eight tetraploids, two hexaploids, and one octoploid. They are facultatively autogamous herbaceous plants capable of reproducing both sexually and asexually (forming stolons late in the flowering season). Based on extensive crossing experiments as well as field and herbarium studies, the relationships among species of this section have been clarified. Internal genetic barriers between species are nonexistent, and natural hybridization is fairly common. Among the diploid species, L. linifolia and L. linearis have very narrow leaves, petaliferous flowers, and elongate capsules. The two species, however, differ chromosomally by one reciprocal translocation. Y x hybrids between them are vigorous, have ca. 50% stainable pollen, and produce moderate quantities of viable seeds. Ludwigia stricta, the Cuban endemic, is apparently most closely allied to L. linifolia, based on morphological evidence, but has not yet been studied biosystematically. Ludwigia microcarpa, in contrast, has spatulate-obovate leaves, small, apetalous flowers, and minute obconical capsules. Artificial hybrids between L. microcarpa and either L. linearis or L. linifolia form neither stainable pollen nor seeds; for the most part, the chromosomes of these hybrids do not pair in meiosis. Ludwigia microcarpa probably evolved relatively early from outcrossing ancestors.Although the nine tetraploid members in sect. Microcarpium are sharply distinct morphologically, they can be crossed in any direction in the experimental greenhouse and form fertile F, offspring. Natural hybrids in plants of this group are also fairly common and in some cases blur the boundaries of the species. Somewhat surprisingly, none of the extant diploid species are considered to be direct ancestors of the tetraploids, based on cytogenetic studies.The two hexaploid species, L. alata and L. simpsonii, are not closely related to each other. The affinity of L. alata is definitely with the tetraploid species group. Hybrids between L. alata and any other tetraploid species consistently exhibit a modal configuration of 16 II and 8 I in meiosis. Based on its morphology and the cytology of hybrids involving it, L. alata may have originated through hybridization between a tetraploid species, possibly L. lanceolata, and the diploid L. microcarpa, or populations ancestral to each of these species.Ludwigia simpsonii 9 on the other hand, is closely related to L. curtissii, which is the only octoploid in sect. Microcarpium. The two species are unique in sect. Microcarpium in having loculicidal capsules and, together with the diploid L. microcarpa, in having spatulate-obovate cauline leaves. Cytogenetic and morphological studies suggest that the octopl...

No abstract

In this study, we investigated the genetic structure and phylogeographic pattern of the genus Cunninghamia, a member of the Cupressaceae restricted to mainland China and Taiwan, based on sequences of the trnD-trnT noncoding spacer of the chloroplast DNA. Maternal inheritance of chloroplasts was determined experimentally. No paternal leakage was detected. Both parsimony and neighbor-joining analyses revealed the polyphyly of Cunninghamia konishii, populations of which were nested in clades of C. lanceolata from mainland China. The nucleotide diversity of chloroplast DNA sequences within C. konishii (0.0118) was higher than that between species (0.0104), which agrees with a previous allozyme investigation. Based on mutational differences between sequences, a minimum spanning network consisting of five clades was constructed. Significant genetic differentiation (phiST = 0.130, P < 0.001) was detected between the clades based on AMOVA analyses. We infer several possible refugia in the Yunnan, Zhejiang, and Guangdong provinces of south China, all located in the minimum network as interior nodes. We also infer possible migration routes of Cunninghamia populations. The phylogeographic pattern shown in the reconstructed network suggests that the present-day Cunninghamia populations in Taiwan were derived from six different sources in continental Asia via long-distance seed dispersal. A migrant-pool model explains the heterogeneous composition of the organelle DNA in Taiwan's populations and the low differentiation between populations of Taiwan and China (phiCT = 0.012, P = 0.454). In contrast with the genetic heterogeneity within geographic populations, many local populations have attained coalescence at the trnD-trnT alleles, which has led to significant differentiation at the population level.

The conservation of Acacia with an Australian type has been perhaps the most controversial issue to have been dealt with under the International Code of Botanical Nomenclature in many years. Before, during and since the vote on the matter at the Seventeenth International Botanical Congress in Vienna, strong opinions have been expressed in print, on the web and in the popular media. Opponents of the Vienna decision are currently focusing on details of the process by which the vote was conducted, rather than on the merits or otherwise of the original proposal. They have signalled an intention to challenge and to try to overturn the Vienna decision at the Melbourne Congress. We are a group of taxonomists, from a range of backgrounds and with a range of opinions on the original proposal, who believe that the Vienna process was fundamentally sound, and that continuance of this argument in its current form is damaging to the international nomenclatural consensus. We provide this paper as, we hope, an objective, non‐partisan summary of the issue and conclude with the recommendation that the international taxonomic community should accept the retypification of Acacia and move on.