Three new species of Senecio (Asteraceae) from Mexico

Senecio moranii, Senecio martirensis, andSenecio semperamatae, all from Mexico, are described as new.     

Two new species of Senecio section Palmatinervii (Asteraceae) from eastern Mexico

Two closely related new species,Senecio grimesii andS. marquezii, belonging to the sectionPalmatinervii are described, illustrated, and compared to their nearest relative,S. heterogamus. An erratum to this article is available at .     

Two new species of Senecio section Palmatinervii (Asteraceae) from northeastern Mexico

Two new species ofSenecio,S. sundbergii andS. neogibsonii, belonging to the sectionPalmatinervii are described, illustrated, and compared to their nearest relatives,S. aschenbornianus andS. lanicaulis.     

Pollen competition among two species of Senecio (Asteraceae) that form a hybrid zone on Mt. Etna, Sicily

Hybridization between interfertile, sympatric or parapatric, plant species can be reduced significantly by conspecific pollen advantage (CPA), whereby conspecific pollen has an advantage over heterospecific pollen in terms of ovule fertilization. We examined CPA in two interfertile species of Senecio, S. aethnensis, and S. chrysanthemifolius (Asteraceae), which form a hybrid zone on Mt. Etna, Sicily. Individuals of both species were pollinated with pollen mixtures containing 0, 25, 50, 75, or 100% heterospecific pollen, and offspring were genotyped to determine if they were products of conspecific or heterospecific pollen fertilizing the ovules. The mean proportion of hybrid offspring produced on S. aethnensis plants was not significantly different to that expected based on the proportion of heterospecific pollen applied to the flower head. However, S. chrysanthemifolius mother plants showed moderate CPA, with the proportion of hybrid offspring significantly less than expected. Seed set or seed germination was not reduced, hence the CPA found for S. chrysanthemifolius acts before ovule fertilization. The consequences of asymmetry in CPA on the reproductive isolation of S. aethnensis are briefly discussed, along with other mechanisms that may play a role in the maintenance of the hybrid zone on Mt. Etna.     

Recurrent origin of peripheral,coastal (sub)species in Mediterranean Senecio (Asteraceae)

Background: It is argued that coastal endemic taxa may evolve in parallel at the periphery of the distributional range of a widespread species.

Aims: We tested this hypothesis for the origins of three peripheral, coastal isolates of Senecio, S. glaucus ssp. glaucus (Israel), S. g. ssp. coronopifolius p.p. (Sicily), and S. hesperidium (Morocco), from widespread S. glaucus ssp. coronopifolius. We also determined the relative roles of selection vs. genetic drift in shaping phenotypic divergence in ssp. glaucus and S. hesperidium, using Lande’s test of neutral morphological change.

Methods: We surveyed morphological and/or allozyme variation in the three peripheral isolates and mainly inland populations of S. g. ssp. coronopifolius.

Results: Genetic data supported independent origins of the coastal taxa from nearby populations of ssp. coronopifolius. These descendant and ancestral populations showed pronounced morphological but weak genetic differentiation. Phenotypic similarities between ssp. glaucus (Israel) and S. hesperidium (Morocco) in plant height and floral traits may have resulted from parallel divergent selection from ssp. coronopifolius, though drift remains an alternative cause in S. hesperidium.

Conclusions: Our results indicate parallel ecotype formation and (sub)speciation in Senecio in which primarily selective vs. neutral determinants promoted the recurrent origin of coastal types in, respectively, Israel and Morocco.     

Reproductive fitness of hybrids between Senecio jacobaea and S. aquaticus (Asteraceae)

Natural hybridization is increasingly recognized as an important process for the ecology and evolution of natural plant populations and species. There is a great need to initiate more studies based on natural populations in order to elucidate the possible role of hybrids in nature. The reproductive success of early generation hybrids can make or break hybrid lineages and may determine the genetic structure of hybrid swarms or the potential for gene flow through future generations, but studies of hybrid reproductive success are lacking. Here we measured components of male and female reproductive success in Senecio jacobaea and S. aquaticus (Asteraceae) species and F(1) hybrids between these species under laboratory conditions, and we measured reproductive output from crosses producing F(1), F(2), and backcross (BC) generation hybrids. F(1) hybrids were readily produced, and on average, the success of crosses producing subsequent generations (F(2), BC) decreased (though remained substantial), but the success of crosses was highly dependent on the genotypes involved. Also, F(1) hybrids were bigger, produced more flowers, and therefore produced more pollen than parental plants. Finally, crosses between parents were asymmetrical, such that S. aquaticus produced more and larger F(1) seeds than did S. jacobaea.     

Population decline despite high genetic diversity in the new allopolyploid species Senecio cambrensis (Asteraceae)

Senecio cambrensis (Welsh groundsel) is a new allohexaploid species, which originated in Wales, UK, in the early part of the 20th century following hybridization between the native tetraploid groundsel (Senecio vulgaris) and the introduced diploid Oxford ragwort (Senecio squalidus). A survey of the number of populations and flowering individuals per population of S. cambrensis in Wales was conducted at peak flowering time in June 2002, 2003 and 2004. The results show a dramatic decrease in both population number and population size of the species since the 1980s when the last population census was conducted. A survey of amplified fragment length polymorphism (AFLP) variation showed that this decline has occurred despite the fact that S. cambrensis contains a high level of genetic diversity with each individual screened possessing a unique multilocus phenotype. The level of variance within the species was similar to that found in one parent (S. vulgaris) and slightly greater than that among samples of the other parent (S. squalidus). Only a small proportion (5%) of AFLP diversity was partitioned among populations indicating a lack of population structure and possibly high levels of gene flow via seed dispersal in what is predominantly a selfing species. Senecio cambrensis showed closer similarity in AFLP phenotype to S. vulgaris than to S. squalidus. Possible causes of this and also the high level of AFLP diversity found in S. cambrensis are discussed. It is suggested that intergenomic recombination following occasional multivalent formation during meiosis in S. cambrensis is likely to be an important cause of both phenomena, although other causes are not ruled out.     

Recent hybrid origin and invasion of the British Isles by a self-incompatible species, Oxford ragwort (Senecio squalidus L., Asteraceae)

Senecio squalidus is a diploid hybrid species which originated in the British Isles following the introduction of material collected from a hybrid zone on Mount Etna, Sicily, approximately 300 years ago. Introduced hybrid material was cultivated in the Oxford Botanic Garden and gave rise to the stabilized diploid hybrid species, which later spread throughout much of the UK and into some parts of Ireland. Unusually for an invasive species, S. squalidus has a strong system of sporophytic self-incompatibility (SSI) that may have become modified as a result of its recent hybrid origin and spread. First, S. squalidus contains relatively few S alleles (between 2 and 6 S alleles within individual UK populations) compared to other species with SSI (estimates average ~17 S alleles per population). This most probably reflects the population bottleneck experienced by introduced hybrid material. Second, dominance relationships among S. squalidus S alleles are more extensive than those reported in other species with SSI. Third, although pseudo-self-compatibility occurs sporadically in S. squalidus, it is not widespread, indicating that SSI is maintained in the species despite potential mate availability restrictions imposed by low numbers of S alleles. Surveys of other forms of genetic diversity in S. squalidus show that allozyme variation is reduced relative to that within the progenitor species, but Randomly Amplified Polymorphic DNA variation is relatively high. Both types of genetic variation show little or no pattern of isolation-by-distance between populations in keeping with the recent range expansion of the species. During its spread in the British Isles, S. squalidus has hybridized with the native self-compatible (SC) tetraploid species, S. vulgaris, which has led to the origin of three new SC hybrid taxa: a radiate form of S. vulgaris (var. hibernicus), a tetrapoid hybrid species (S. eboracensis) and an allohexaploid (S. cambrensis).     

Natural hybrids in Senecio (Asteraceae): new records from Argentina

Abstract

Hybridisation is very common within Senecio. It is considered a fundamental mechanism of speciation and also a major feature causing systematic complexity. Morphological features are the preliminary characteristics used to identify hybrids; however this approach is usually not sufficient when this is the case chromosome studies represent a valuable tool for reinforcing the observations. Two natural homoploid interspecific hybrids are reported here: Senecio × lulioi M. G. López et Xifreda (S. brasiliensis (Spreng.) Less. × S. grisebachii Baker) and Senecio × piepaloensis M. G. López et Xifreda (S. ragonesei Cabrera × S. sectilis Griseb.). Classic cytogenetic analysis and pollen stainability were performed to evaluate hybrid origins and to designate the putative parents. S. × lulioi presented a low frequency of quadrivalents and heteromorphic bivalents, both strong evidences of hybridisation between closely related species. S. × piepaloensis exhibited a high frequency of meiotic irregularities, and reduced pollen stainability, certain characteristics of hybrids. This analysis is discussed in relation to the role of hybridisation in the evolution of the genus, and its systematic significance.     

Chromosome numbers and meiotic studies in species of Senecio (Asteraceae) from Argentina

Meiotic chromosome counts, chromosomal behaviour and meiotic configurations of ten taxa of Senecio from Argentina were examined. Most counts are original: S. crepidifolius DC., S. francisci Phil. and S. octolepis Griseb. var. saltensis (Hicken) Cabrera & Zardini have 2 n  = 40, and S. chrysolepis Phil., 2 n  = 80 + 8B. We confirmed previous reports for S. deferens Griseb. (2 n  = 40 + 4B), S. filaginoides DC. var. filaginoides (2 n  = 40), S. hieronymi Griseb. (2 n  = 40 + 7B), S. pampeanus Cabrera (2 n  = 40) and S. rudbeckiifolius Meyen & Walp. (2 n  = 40 + 7B). In S. bracteolatus Hook. & Arn. var. bracteolatus , we found a new number (2 n  = 40) that differs from the one cited previously. In four species, numerical polymorphisms for B-chromosomes were observed. Several of the analysed species presented secondary bivalent association. This phenomenon, together with other evidence, supports x  = 5 as the basic chromosome number. The number of chiasmata and their positions were also surveyed, with the finding that open bivalents were the most frequent meiotic figures and terminal chiasmata the preferential position. These features are related to recombination rate, and the success and persistence of these polyploids. We discuss some systematic and evolutionary aspects in the light of cytogenetic data and conclude that polyploidy is the major force modelling the chromosome evolution within this genus.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 148 , 465–474.     

Jalcophila boliviensis,a new species of South American Asteraceae (Gnaphalieae)

The new species, Jalcophila boliviensis (Asteraceae: Gnaphalieae) is described and illustrated. A discussion of the systematic position of Jalcophila Dillon & Sagást. and a key to the three species of the genus are presented.     

A new species of Brickellia,subgenus Phanerostylis (Asteraceae)

Brickellia nesomii, a new species from northeastern Mexico, is described. It belongs to the subgenus Phanerostylis, which Gray originally placed in Eupatorium; King and Robinson elevated the taxon to generic rank; it is herein kept at the subgeneric level but transferred to Brickellia. Reasons for this transfer are given. Barroetea glutinosa, positioned by King and Robinson in Phanerostylis, is excluded.     

Origins, establishment and evolution of new polyploid species: Senecio cambrensis and S. eboracensis in the British Isles

Two new polyploid species of Senecio have originated in the British Isles in recent times following hybridization between native S. vulgaris (2 n  = 40) and introduced S. squalidus (2 n  = 20). One of these is the allohexaploid S. cambrensis (2 n  = 60), the other is the recombinant tetraploid S. eboracensis (2 n  = 40). We review what is known about when and how each species originated, and their reproductive isolation from parents due to high selfing rates. We also review evidence that suggests S. cambrensis may have undergone rapid genome evolution since its origin, and comment on the risks of extinction to each species due to chance factors operating during the early establishment phase. The discovery of both species soon after their origin provides an unparalleled opportunity to examine two different but related forms of speciation following hybridization between the same parent species. Further detailed study of the ecology and genomics of S. cambrensis and S. eboracensis will help improve our understanding of the process of polyploid speciation in plants.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 467–474.     

Lopholaena festiva, a new species from the Transvaal, South Africa (Asteraceae)

A new species of Lopholaena, L. festiva , is described from the northern Transvaal, South Africa. It's affinities are discussed. A distribution map is presented. The tribal disposition of the genus Lopholaena is reviewed.     

A new species of Scorzonera (Asteraceae) from Khorasan, Iran

Scorzonera joharchii sp. nov. is described from the Khorasan, east of Birjand, Iran. It is similar to S. tuberosa from which it mainly differs in its tomentose indumentum, longer pappus and villous and longer achenes.     

A new species of Scorzonera (Asteraceae) from Anatolia, Turkey

Scorzonera aytatchii sp. nov. is described from the Aydos Mountain (C4: Konya) in Turkey. It is related to S. rigida , from which it mainly differs in its hairy achene.     

Two new species of Grindelia (Astereae,Asteraceae) from Uruguay

Taxonomic revision of South American species ofGrindelia Willd. has revealed two new species from Uruguay:G. rupestris, an erect subshurb with crowded obovate denticulate leaves, subsessile heads, and pappus composed of numerous awns, andG. linearifolia, a prostrate shrublet with small entire linear leaves. Both species are described and illustrated. A key for the UruguayanGrindelia species is provided.