Cytology and embryology of the pompom weed,Campuloclinium macrocephalum (Eupatorieae,Asteraceae)

Campuloclinium macrocephalum (Less.) DC. is a perennial herb widely distributed in the New World, but introduced to South Africa, where it is commonly called “pompom weed”. This species is considered one of the most important weeds from Brazil and it has been included among the plant invaders of South Africa. Results of the meiotic and embryological analyses of six populations of C. macrocephalum are reported in this paper. The microsporogenesis analysis revealed five triploid (2n = 3x = 30) and one diploid (2n = 2x = 20) populations with a basic chromosome number x = 10. The diploid specimens showed regular meiotic behavior, but the triploid plants presented irregular chromosome pairing which result in the formation of univalents, bivalents and trivalents at diakinesis. In consequence, laggard chromosomes, unbalanced nuclei and micronuclei were observed in subsequent phases of meiosis. The embryological analysis showed that the triploid specimens of C. macrocephalum have embryo sac development from a nucellar cell (apospory), which indicates that these specimens are apomictic. Almost all cases of apomixis found in tribe Eupatorieae are diplosporous apomixis. Campuloclinium macrocephalum constitutes the second species of the tribe and the first of the genus with apospory as reproductive system. The aposporous apomixis combined with the presence of xylopodium would be two important factors responsible for the invasiveness of C. macrocephalum.     

Pollen morphology and its relation with meiotic irregularities in ten species of Campuloclinium (Eupatorieae,Asteraceae)

Pollen grains of ten species of Campuloclinium (Eupatorieae, Asteraceae) are described and illustrated using light and scanning electron microscopy. The species included in this study are C. burchelli, C. campuloclinioides, C. chlorolepis, C. hirsutum, C. irwinii, C. macrocephalum, C. megacephalum, C. parvulum, C. purpurascens and C. riedelli. Pollen grains of Campuloclinium are typically radially symmetric, echinate, tectate, oblate-spheroidal to prolate-spheroidal (P/E ratio: 0.94–1.10). Pollen is mostly triaperturate, but tetraaperturate or biaperturate pollen also occurs in some species. The pollen diameter was highly variable ranging from 10.54 µm to 36.18 μm. The significance of the variation in type and size of pollen is discussed in relation to diverse meiotic abnormalities and possible reproductive apomictic processes within the polyploid species.     

Taxonomy ofCarminatia (Asteraceae,Eupatorieae)

A taxonomic study of the largely Mexican genusCarminatia is rendered. It is comprised of three closely related species:C. tenuiflora, C. recondita andC. anomala spec. nova. Illustrations, dot maps, keys to species and complete synonymy are presented.     

Mating interactions between coexisting dipoloid, triploid and tetraploid cytotypes ofHieracium Echioides (Asteraceae)

Experimental crosses between diploids, triploids and tetraploids ofHieracium echioides were made to examine mating interactions. Specifically, cytotype diversity in progeny from experimental crosses, intercytotype pollen competition as a reproductive barrier between diploids and tetraploids, and differences in seed set between intra- and intercytotype crosses were studied. Only diploids were found in progeny from 2x × 2x crosses. The other types of crosses yielded more than one cytotype in progeny, but one cytotype predominated in each cross type: diploids (92%) in 2x × 3x crosses, tetraploids (88%) in 3x × 2x crosses, triploids (96%) in 2x × 4x crosses, triploids (90%) in 4x × 2x crosses, tetraploids (60%) in 3x × 3x crosses, pentaploids (56%) in 3x × 4x crosses, triploids (80%) in 4x × 3x crosses and tetraploids (88%) in 4x × 4x crosses. No aneuploids have been detected among karyologically analyzed plants. Unreduced egg cell production was detected in triploids and tetraploids, but formation of unreduced pollen was recorded only in two cases in triploids. Triploid plants produced x, 2x and 3x gametes: in male gametes x (92%) gametes predominated whereas in female gametes 3x (88%) gametes predominated. Cytotype diversity in progeny from crosses where diploids and tetraploids were pollinated by mixture of pollen from diploid and tetraploid plants suggested intercytotype pollen competition to serve as a prezygotic reproductive barrier. No statistically significant difference in seed set obtained from intra- and intercytotype crosses between diploids and tetraploids was observed, suggesting the absence of postzygotic reproductive barriers among cytotypes.     

Cytogenetics, geographical distribution, and pollen fertility of diploid and tetraploid cytotypes of Santolina pectinata Lag. (Asteraceae: Anthemideae)

A cytogenetic study of 62 populations of Santolina pectinata in Spain shows the existence of two ploidy levels. The diploid cytotypes with 2 n  = 18 occupy the eastern Betic mountains, and the tetraploid cytotypes with 2 n  = 36 are located on the spurs of the Iberian System. The former show a much wider ecological spectrum than the latter. Mixed cytotypes were observed in two diploid populations, with one tetraploid in each, showing different karyotypes. Three trisomic individuals were detected, one in a diploid population and the other two in a tetraploid population. Also, three hypotetraploid individuals were detected in a tetraploid population. Polyploidy is shown to be spontaneous and recurrent, promoting partial sterility in the pollen. Structural chromosomal changes, principally translocations, and local speciation through autopolyploidy are the principal factors in the evolution and diversification of this species.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 657–667.     

Hybrid genera in Liatrinae (Asteraceae: Eupatorieae)

Liatrinae is a small subtribe of Eupatorieae that occurs in North America with a center of generic-level diversity in the southeastern United States. Molecular phylogenetic data were sought to assess whether two monotypic genera, Garberia and Hartwrightia, are accurately placed in the subtribe, and to resolve questions of the generic-level classification of Carphephorus. Phylogenetic analyses of nuclear ITS/ETS and plastid DNA data indicated that Garberia is the basalmost diverging lineage, and that Hartwrightia is phylogenetically embedded in the subtribe. There was significant incongruence between the ITS/ETS and plastid DNA datasets in the placement of Hartwrightia and another monotypic genus, Litrisa, suggesting that both are of original hybrid origin. The results also showed that Carphephorus s.l. is not monophyletic, and even after removal of the two species of Trilisa, it is still paraphyletic to Liatris. The apparent hybrid origin of Hartwrightia, which is morphologically transgressive relative to its inferred parental lineages, suggests that reticulation between phylogenetically distinct lineages may be a recurrent problem for phylogenetic estimation in Asteraceae.     

Liothrips tractabilis sp.n. (Thysanoptera: Phlaeothripinae) from Argentina, a potential biocontrol agent of Weedy Campuloclinium macrocephalum (Asteraceae) in South Africa

A new species, Liothrips tractabilis, is described from northern Argentina. Feeding by this thrips causes severe damage to the leaves of Campuloclinium macrocephalum, a plant that has been introduced to South Africa where it is a serious weed of grasslands. A key is provided to the four species of the genus Liothrips recorded from Argentina.     

Meiotic behaviour and pollen fertility in three species of Zephyranthes (Amaryllidaceae)

Studies on meiotic behaviour and pollen fertility have been carried out in Zephyranthes candida, Z. grandiflora and Z. flava. Maximum meiotic abnormalities in chromosome behaviour were observed in Z. candida and Z. grandiflora. There were variations in the number of bivalent formation, multivalents and anaphasic separation. All types of abnormalities were found to be associated with low percentage of pollen fertility. In Z. flava, chromosomal aberrations were low and pollen fertility was high. This revised version was published online in July 2006 with corrections to the Cover Date.     

Coexistence of diploid, triploid and tetraploid crucian carp (Carassius auratus) in natural waters

Background

Crucian carp (abbreviated CC) belongs to the genus of Carassius within the family of Cyprinidae. It has been one of the most important freshwater species for Chinese aquaculture and is especially abundant in the Dongting water system of Hunan province. CC used to be considered as all diploid forms. However, coexistence of diploid (abbreviated 2nCC), triploid (abbreviated 3nCC) and tetraploid crucian carp (abbreviated 4nCC) population of the Dongting water system was first found by our recently researches.

Results

We examined the ploidy level and compared biological characteristics in different ploidy CC. In reproductive mode, 2nCC was bisexual generative and 4nCC generated all-female offspring by gynogenesis. However, 3nCC generated progenies in two different ways. 3nCC produced bisexual triploid offspring fertilized with 3nCC spermatozoa, while it produced all-female triploid offspring by gynogenesis when its ova were activated by heterogenous spermatozoa. The complete mitochondrial DNA of three different ploidy fishes was sequenced and analyzed, suggesting no significant differences. Interestingly, microchromosomes were found only in 3nCC, which were concluded to be the result of hybridization. Allogenetic DNA fragments of Sox genes were obtained in 3nCC and 4nCC, which were absent in 2nCC. Phylogenetics analysis based on Sox4 gene indicated 3nCC and 4nCC formed a separate group from 2nCC.

Conclusions

In summary, this is the first report of the co-existence of three types of different ploidy crucian carps in natural waters in China. It was proved that the coexistence of different ploidy CC was reproductively maintained. We further hypothesized that 3nCC and 4nCC were allopolyploids that resulted from hybridization. The different ploidy CC population we obtained in this study possesses great significance for the study of polyploidization and the evolution of vertebrates.     

Meiotic behavior and pollen morphology variation in Centaurium pulchellum (Gentianaceae)

Centaurium pulchellum is an annual herb native to Europe, but introduced in South America, where it is widely used in the preparation of digestive infusions and bitter drinks. In this species, a wide variation in the aperture pattern of pollen grains was reported and has been attributed to environmental factors or irregularities at meiosis. For this reason, cytological and palynological studies have been undertaken on two different populations. The pollen grain analysis showed that some types are more frequent within each population, but the most common forms were the typical 3-colporate and 4-colporate. The cytological analysis revealed that the analyzed populations of C. pulchellum have chromosome number 2n = 36. The presence of tetravalents at meiosis strongly suggests that these populations are autotetraploid based on x = 9. The meiotic behavior showed a significant percentage of irregularities in different phases: off-plate bivalents, precocious segregation, laggard chromosomes, bridges, and cytomixis. However these irregularities are not related to the variation in the aperture pattern of pollen grains. The heteromorphism in the pollen grains observed in C. pulchellum could be a normal condition to which the species is well adapted.     

Response of the invasive pompom weed,Campuloclinium macrocephalum (Asteraceae), to feeding by the foliage-deforming thrips Liothrips tractabilis (Phlaeothripidae) under outdoor conditions in South Africa

The foliage-deforming thrips Liothrips tractabilis Mound and Pereyra (Thysanoptera: Phlaeothripidae) was recently released in South Africa as the first classical biological control agent against the invasive South American herb, Campuloclinium macrocephalum (Less.) DC. (Asteraceae). The impact of the thrips on young plants and regrowth of C. macrocephalum was assessed under outdoor conditions, and the results were compared to those of earlier laboratory trials that were conducted while the agent was still under investigation in quarantine. The outdoor trials revealed that feeding by L. tractabilis reduced the growth and biomass accumulation of C. macrocephalum, particularly in young plants and to a lesser extent in regrowth, which was largely consistent with the results of the earlier laboratory trials. Thrips-infested young plants were significantly shorter, produced fewer leaves and displayed significantly lower wet root masses and lower below- and above-ground dry masses, compared to the control plants. Although thrips-infested regrowth were significantly shorter, produced fewer leaves and displayed significantly lower above-ground dry masses than the control plants, the differences in wet root masses and below-ground dry masses were not significant. Although laboratory-based impact assessments are not necessarily an accurate reflection of field impact, in this instance the results were largely validated by the outdoor assessments. The results suggest that L. tractabilis will have a negative impact on C. macrocephalum populations in the field and thus contribute towards the weed’s biological control. The establishment of L. tractabilis has recently been confirmed in South Africa, providing the opportunity to verify these predictions.     

Geographical distribution of Eupatorieae (Asteraceae) in South-eastern and South Brazilian Mountain Ranges

This study deals with the geographical distribution of Eupatorieae species in South-eastern and Southern Brazilian mountain ranges, with special emphasis on the Mantiqueira range (Serra da Mantiqueira). In the Mantiqueira range, five localities were sampled for two years during the flowering period of the plants. Species composition in the Mantiqueira localities was then compared to data from a central range (the Espinhaço) and a southern coastal range. Cluster and ordination analyses showed clear floristic differences among the three ranges. Nearer localities were more similar floristically only within the Espinhaço range and across all ranges, as shown by Mantel tests. The dendrogram in the Mantiqueira range clustered Itatiaia and Campos do Jordão, two non-adjacent localities with similar environment, landscape and topography. Different processes may be influencing the structure and composition of the Eupatorieae flora at different geographical scales. Historical and biogeographical processes may be more important in determining community composition of different mountain ranges, whereas factors such as climate and human impact may be determining differences among localities within each mountain range.     

Unreduced gametes and neopolyploids in natural populations of Achillea borealis (Asteraceae)

Polyploidy is a major mechanism of speciation and adaptation, yet little is known about the origins of polyploids in natural species. I investigated gametic nonreduction and neopolyploid formation in natural tetraploid populations of Achillea borealis (Asteraceae), an autopolyploid complex consisting of tetraploid and hexaploid cytotypes. Cytological analyses of tetraploid populations revealed the occurrence of reduced (n=2x) as well as unreduced 'big' (2n=4x) and 'jumbo' (4n=8x) pollen grains, which were clearly distinguished by size. Production of unreduced pollen was monitored in two tetraploid populations in 1997 and 1998. Mean population-level frequencies of unreduced pollen ranged from 0.030 to 0.538%, with as few as one-third and as many as one-half of sampled plants producing unreduced grains. Eight individuals were found to produce >1% unreduced pollen, with highest observed frequencies of 7.0, 13.2 and 15.8%. Experimental crosses using high unreduced pollen producers as male parents generated viable seeds. However, the frequency of neohexaploids in the progeny of experimental crosses (0.388%) was similar to that observed in progeny of randomly selected, open-pollinated control parents (0.465%). These results suggest that unreduced eggs are the most likely source of new polyploids. In spite of the inefficiency of unreduced pollen in unilateral sexual polyploidization, the overall rate of neohexaploid formation (one in 233) was several orders of magnitude greater than estimates of genic mutation rates.     

Meiotic behavior and pollen viability in Moringa oleifera (Moringaceae) cultivated in southern Brazil

Although originally from India, Moringa oleifera is now cultivated throughout most of the tropics, including Brazil. Despite its multipurpose value for food and traditional medicine, little is known about the meiotic behavior and pollen viability of M. oleifera. We evaluated microsporogenesis and pollen viability in eleven plants grown in southern Brazil (Maringá, Paraná). Bud flowers were collected in different stages of development. All plants that we analyzed presented 2n = 28 chromosomes, as previously reported for this species. Chromosomes paired as bivalents. Meiotic abnormalities were rare and metaphase I was the most affected phase. Pollen viability was superior to 88%. Tripolar spindles in metaphase II, leading to the formation of unreduced gametes, were recorded in some plants at a low frequency.     

A new species of Ageratina (Asteraceae: Eupatorieae) from northwestern Oaxaca

Fieldwork in connection with the project to document the flora of the Mixteca Alta region, northwestern Oaxaca, Mexico, has resulted in the discovery of a new species, Ageratina pendula.