Karyology of some Convolvulaceae species occurring in NE Brazil inselbergs

Eighteen species belonging to family Convolvulaceae occurring in northeastern Brazil were analyzed to identify the karyotypic variability among rupicolous and non-rupicolous species. The count of 2n = 56 for Evolvulus sp., is the first report of polyploidy for the genus. The similarities among the karyotypes of species of Ipomoea, Merremia, and Operculina suggest that x = 15 is the basic secondary number for these genera, while x = 13 has been observed in Evolvulus. The genus Jacquemontia, with 2n = 18 is karyologically distinct from the other genera of the family. Intraspecific numerical chromosomal variations were not detected, nor were any karyological variations related to the rocky habitat characteristic of inselbergs. The occurrence of other plant groups with polyploid forms linked to this type of habitat suggests that the family Convolvulaceae is karyologically stable. We discuss variations in chromosome numbers, base numbers, and their implications in the evolution of the principal groups within the Convolvulaceae.     

斑腿蝗科10属NOR定位及其细胞分类学意义

本文以银染技术对我国斑腿蝗科10个属的代表种类进行了核仁组织者区域(NOR)定位研究。结果表明:NOR位置在同属内不同种间显示出种间相似性,而不同属间则有差别,揭示了属内同源性。     

Molecular phylogeny of the genus Dahlia Cav. (Asteraceae, Heliantheae-Coreopsidinae) using sequences derived from the internal transcribed spacers of nuclear ribosomal DNA

Sequences of the internal transcribed spacers (ITS) of the 18S-26S nuclear ribosomal DNA were used to resolve phylogenetic relationships among 13 species of the genus Dahlia . Phylogenetic reconstruction from both parsimony analysis and pairwise distance data produced a single tree in which four clades could be distinguished, these broadly separating the species into the different chromosome numbers found in Dahlia ( x = 16, x = 17 and x = 18). Although species based on x = 16 were divided into two clades, there is the suggestion that this separation may be artificial and that these should be combined as a single clade. The phylogeny produced here has been discussed with reference to the existing taxonomic treatment of the genus. It currently appears that the genus Dohlia is monophyletic and it is evident that the different basic chromosome numbers withim the dysploid series in Dahlia have evolved only once. This proposed monophyly of the genus coupled with the successful production of hybrids withim the dysploid series (2 n = 32, 2 n = 34 and 2 n = 36) suggests that the species of Dahlia have evolved from a common ancestor.     

新疆、青海和四川等地区小麦族植物的细胞学观察

本文对采集于新疆、青海和四川等地的小麦族(Triticeae Dumortier)10属、52种、370份种子材料进行了细胞学观察。该地区小麦族各属种的染色体数目变化范围是从2n=14到2n=84,前者主要存在于大麦属(Hordeum)、新麦草属(Psathyrostachys)和黑麦属(Secale),而后者全部集中于赖草属(Leymus)。其中染色体数目为2n=28和2n=42的类型出现的频率很高,大多存在于鹅观草属(Roegneria)和披碱草属(Elymus)。除个别种内存在不同倍性的细胞型外,绝大多数种的染色体数目非常稳定。在所有的样本中均没有观察到具非整倍体和B-染色体的材料。     

Mechanisms of karyotype evolution in the Brazilian scorpions of the subfamily Centruroidinae (Buthidae)

The recently-revised subfamily Centruroidinae is part of the New World clade of buthid scorpions. In this study, we analyzed the cytogenetic characteristics of nine of the 10 Brazilian centruroidines, and one undescribed species of the genus Ischnotelson, using a phylogenetic approach to determine the chromosomal rearrangements responsible for the differentiation of karyotypes among the species. The cytogenetic data recorded in the present study supported the new taxonomic arrangement of the Centruroidinae, with all the species of the same genus sharing the same or similar diploid numbers, i.e., 2n?=?20 or 22 in Troglorhopalurus lacrau and T. translucidus, 2n?=?25 or 26 in Ischnotelson sp., I. guanambiensis and I. peruassu, and 2n?=?28 in Jaguajir agamemnon, J. pintoi and J. rochae. The karyotype modelling in the ChromEvol software indicated 2n?=?18 as the ancestral diploid number of the Centruroidinae. The differentiation of karyotypes among the centruroidine genera was based on increasing chromosome numbers resulting from progressive fission events. These changes probably occurred prior to the diversification of the genera Ischnotelson, Jaguajir, Physoctonus and Rhopalurus, and appear to have played a more important role in karyotype evolution at the intergeneric level than the interspecific one. However, the observed increase in diploid numbers was not accompanied by changes in the number or location of ribosomal genes or telomeric sequences. The identification of meiotic cells in female specimens also allowed us to discuss the mechanisms of achiasmatic meiosis in scorpions.     

Chromosome Numbers in the Genera Cousinia, Olgaea and Syreitschikovia (Compositae)

The scarce karyological data available for both the Arctium-Cousinia complex and the Onopordum group has led us to provide more data essential to understand the karyological evolution of these taxa. Chromosome counts were made on somatic metaphases using the squash technique. We report 20 chromosome number records for the genus Cousinia s. lat. from the area of Near East and Central Asia. Thirteen of them are first chromosome counts for the studied species, and the remaining seven records provide confirmation of scarce or uncertain previous data. We also present the first chromosome counts for three of the 13 sections of this genus. Our records for Arctioid species show karyological uniformity with 2n=36. In the Cousinioid group, 13 records agree with the three major numbers of its characteristic dysploidy series 2n=22, 24 and 26. We report first chromosome counts for the genera Olgaea and Syreitschikovia from Kazakhstan, being 2n=26 and 24, respectively. Our results confirm a hypothesis that the Arctioid and Cousinioid clades, although forming a monophyletic group, have followed different evolutionary paths. In the Onopordum group, our results confirm the existence of two lineages; the colonizing biennial taxa are characterized by n?=?17, while the perennial genera have n?=?12, 13. The evidence for recent polyploidization is absent in both the Arctium-Cousinia complex and the Onopordum group.     

Evolution of chromosome number in mealybugs (Pseudococcidae: Homoptera)

Chromosome numbers of over 90 species of mealybugs are presented (71 for the first time). The diploid chromosome number (2n) ranged from 8 to 64, but over 68% of the species had 2n=10, and 10 is considered to represent the ancestral 2n in this family. Since only 4 species had 2n<10,and 26 had 2n>10, it is concluded that in this family increases in 2n occurred much more often than decreases. The data are compared to those from two other coccid families, the Diaspididae and the Eriococcidae. Unexpectedly, in both the Pseudococcidae and the Diaspididae the frequency of species with the modal 2n is lowest among species from monotypic genera and from genera from which only a single species was examined, and increases with the increase in the number of species examined per genus.(died June 10, 1977)     

安徽黄山木本植物区系中一些种的细胞学研究（Ⅰ）

报道了黄山地区１８种木本植物的染色体数,分属于１５个科中的１８个属,其中１４种和２个属为首次报道;同时对Ａｐｈａｎａｎｔｈｅ,Ｆｏｒｔｕｎｅａｒｉａ,Ｌｏｒｏｐｅｔａｌｕｍ,Ｈｏｌｂｏｅｌｌｉａ,Ｐｌａｔｙｃａｒｙａ属的染色体数及其在分类上的意义作了简单讨论。     

两种木本植物染色体数目的研究

<正> 我国是区系植物十分丰富的国家,有许多特有种及优良用材树种,但其中大多数缺少细胞学研究,近年来我国植物学界虽作了大量的植物染色体的研究工作,但对于木本双子叶植物的染色体数目报导仍然不多。 作者对我国特产的喜树(Camptotheca acuminata Decne. )及优良树种香椿 (Toona sinensis(A. Juss. )Roem. )作了染色体计数的研究。该两种植物以前均未见有染色体数目的报导。     

Molecular phylogeny of the medaka fishes genus Oryzias (Beloniformes: Adrianichthyidae) based on nuclear and mitochondrial DNA sequences

The phylogenetic relationships among medaka fishes of 2 genera, Oryzias and Xenopoecilus, were studied using the nuclear tyrosinase and mitochondrial 12S and 16S rRNA genes. Of the 23 species currently described for these genera, 13 species of Oryzias and 2 species of Xenopoecilus were examined. The tree topologies obtained from the nuclear and mitochondrial data were consistent, indicating that Xenopoecilus is a polyphyletic genus nested within Oryzias. This result suggested the necessity for a systematic study and taxonomic revision of Xenopoecilus. The combined data analysis of all data partitions resulted in a well-resolved tree, with most internal branches supported by high statistical values. Based on our combined data phylogeny, we divided the Oryzias species into three major species groups, namely the latipes, javanicus, and celebensis groups. These three groups corresponded to the three chromosomal groups (biarmed, monoarmed, and fused chromosome groups) previously proposed from karyological analyses. The phylogeographic pattern suggests historical vicariance between Sulawesi Island and the continental shelf.     

Global stingless bee phylogeny supports ancient divergence,vicariance, and long distance dispersal

Stingless bees (Meliponini) are one of only two highly eusocial bees, the other being the well studied honey bee (Apini). Unlike Apini, with only 11 species in the single genus Apis, stingless bees are a large and diverse taxon comprising some 60 genera, many of which are poorly known. This is the first attempt to infer a phylogeny of the group that includes the world fauna and extensive molecular data. Understanding the evolutionary relationships of these bees would provide a basis for behavioural studies within an evolutionary framework, illuminating the origins of complex social behaviour, such as the employment of dance and sound to communicate the location of food or shelter. In addition to a global phylogeny, we also provide estimates of divergence times and ancestral biogeograhic distributions of the major groups. Bayesian and maximum likelihood analyses strongly support a principal division of Meliponini into Old and New World groups, with the Afrotropical+Indo‐Malay/Australian clades comprising the sister group to the large Neotropical clade. The meliponine crown clade is inferred to be of late Gondwanan origin (approximately 80 Mya), undergoing radiations in the Afrotropical and Indo‐Malayan/Australasian regions, approximately 50–60 Mya. In the New World, major diversifications occurred approximately 30–40 Mya. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 206–232.     

The Order Euplotida (Ciliophora): Taxonomy, with Division of Euplotes into Several Genera

ABSTRACT. The order Euplotida represents a monophyletic order of five families of hypotrich ciliates united by morphology, stomatogenesis, ultrastructure, cyst structure, and behavior. A review of variability of ciliation and nuclei among the 14 genera suggests that lines of evolution may have involved both the loss of cirri and nuclear simplification. We present a binary key to genera in the families Aspidiscidae ( Aspidisca and Euplotaspis ), Certesiidae n. fam. ( Certesia ), Gastrocirrhidae ( Cytharoides, Euplotidium , and Gas-trocirrhus ), Uronychiidae ( Diophryopsis, Diophrys, Paradiophrys , and Uronychia ), and Euplotidae. The latter family contains species formerly in the genus Euplotes. Based primarily on cortical structure, endosymbionts, data from morphometric analysis, and ecology, we recognize four different groups. The first group of species remains in Euplotes with Euplotes charon as type. We place a second group of species into the genus Moneuplotes Jankowski 1979 with Moneuplotes vannus (Müller, 1786) as type. We erect two new genera: Euplotoides n. g. and Euplotopsis n. g. with Euplotoides patella (Müller, 1773) n. comb. and Euplotopsis affinis (Dujardin, 1841) n. comb. as type species respectively. We discuss possible phylogenetic relationships within the order.     

New Chromosome Counts of Some Dicots in the Sino-Japanese Region and Their Systematics and Evolutionary Significance

New somatic chromosome numbers for nine species eight families and eight gen era in the Sino-Japanese Region are reported here as shown in Table 1. Data of six genera are previously unknown cytologically. The bearings of these new data on the systematics and evolution of the related species, genera or families are discussed as follows: (1) Platycarya strobilacea Sieb. et Zucc. (Juglandaceae). The chromosome number of this species is 2n=24, with a basic number of x=12, which deviates from 2n=32 occurred in Juglans, Carya, Pterocarya and Engelhardtia with the basic number x= 16. The Juglandaceae appears to be fundamentally paleotetraploid, with an original basic number of x = 6 in Platycarya and x-8 in the other four genera, although secondary polyploidy occurs in Carya. Based on the remarkable morphological differences between Platycarya and the rest seven genera of the family, Manning (1978) established two subfamilies: Platycaryoideae for Platycarya and Juglandoideae for the other genera. Iljinskaya (1990), however, recently established a new subfamily: Engelhardioideae for Engelhardtia. Lu (1982) points out that because of a great number of primitive characters occurring in Platycarya, the genus could not be derived from any other extant juglandaceous taxa but probably originated with the other groups from a common extinct ancestor. The present cytological data gives support to Manning′s treatment. We are also in favor of Lu′s supposition and suggest that basic aneuploid changes, both ascending and descending, from a common ancestor with the original basic number x=7, took place during the course of early evolution of the Juglandaceae and led to the origin of taxa with x=6 and 8. Subsequent polyploidy based on these diploids occurred and brought forth polyploids of relic nature today, whereas their diploid progenitors apparently have become extinct. (2) Nanocnide pilosa Migo (Urticaceae). The chromosome number of this Chinese endemic is 2n-24, with a basic number of x=12. An aneuploid series occurs in the Urticaceae, with x--13, 12, I1, 10, 9, 8, 7, etc. According to Ehrendorfer (1976), x = 14, itself being of tetraploid origin, is the original basic number of the whole Urticales, and descending aneuploid changes took place in the early stage of evolution of the Urticaceae and Cannabinaceae. In addition to Nanocnide, x= 12 also occurs in Australina, Hesperonide and Lecanthus, and partly in Chamabainia, Elatostema, Girardinia, Pouzolzia and Urtica. (3--4) Sedum sarmentosum Bunge and S. angustifolium Z. B. Hu et X. L. Huang (Crassulaceae). The former is a member of the Sino-Japanese Region, while the latter is only confined to eastern China. The chromosome number of Sedum is remarkably complex with n=4-12, 14-16…74, etc. S. angustifolium with 2n=72 of the present report is evidently a polyploid with a basic number of x =18 (9^?) Previous and present counts of S. sarmentosum show infraspecific aneupolyploidy: n = c. 36 (Uhl at al. 1972) and 2n=58 (the present report). These two species are sympatric in eastern China and are morphologically very similar, yet distinguishable from each other (Hsu et al. 1983) S. sarmentosum escaped from cultivation in the United States gardens exhibited high irregularity in meiosis (Uhl et al. 1972). Uhl (pets. comm. ) suspected strongly that it is a highly sterile hybrid. R. T. Clausen (pets. comm.) found that plants of S. sarmentosum naturalized in the American Gardens propagated by means of their long stolons and broken stem tips, and could not yield viable seeds. Hsu et al. (1983) found that some of the plants of S. sarmentosum and S. angustifolium did yield a few seeds, but other did not. These species are, therefore, by the large vegetatively apomictic. (5) Glochidion puberum (L. ) Hutch. (Euphorbiaceae). The genus Glochidion includes about 300 species, but only eigth species from the Himalayas have been studied cytologically, with n= 36 and 2n= 52, having a basic number of x= 13. The present count for the Chinese endemic G. puberum establishes the tetraploid chromosome number 2n= 64, and adds a new basic number x= 16 to the genus. (6) Orixa japonica Thunb. (Rutaceae). Orixa is a disjunct Sino-Japanese monotypic genus. Out of the 158 genera of the Rutaceae, chromosome numbers of 65 genera have hitherto been investigated, of which 42 genera are with x=9 (66.61%), some with x=7, 8 and 10, and rarely with x=13, 15, 17 and 19. The present count of 2n=34 for O. japonica may have resulted from a dibasic tetraploidy of n=8+9. (7) Rhamnella franguloides (Maxim.) Weberb. (Rhamnaceae). The chromosome number of this member of the Sino-Japanese Region is 2n= 24. with a basic number of x= 12. The basic number x= 12 also occurs in Hovenia, Paliurus, Sageretia, Ceanothus and Berchemia. Hong (1990) suggested that x= 12 in Rhamnaceae may be derived from descending aneuploidy of a paleotetraploid ancestor. (8) Sinojackia xylocarpa Hu (Styracaceae). The chromosome number of this rare Chinese endemic is 2n= 24, with a basic number of x =12, which is identical with that in Halesia and Pterostyrax, but deviates from that in Styrax (x=8). The basic number x=8 in the Styracaceae may be derived from the original basic number x=7 by ascending aneuploidy in the early stage of evolution of the family, and x=12 may be derived from polyploidy. (9) Thyrocarpus glochidiatus Maxim. (Boraginaceae). The chromosome number of this Chinese endemic species is 2n=24, with a basic number of x=12. An extensive aneuploid sequence of x = 4-12 occurs in the Boraginaceae, of which x = 8, 7 and 6 are the most common. The basic number x=12 also occurs in Cynoglossum and Mertensia. It is evident that aneuploid changes, both descending and ascending, from an ancestor with x = 7, have taken place in the primary phase of evolutionary diversification of the Boraginaceae, and subsequent polyploidy has given rise to x=15, 17 and 19 in a few genera (e. g. Amsinskia and Heliotropium). The origin of x=12 is not certain. Either it be a result of ascending aneuploidy, or a product of polyploidy on the basis of x = 6. The present authors are in favorof the latter.     

Study of the evolutionary relationships among Limonium species (Plumbaginaceae) using nuclear and cytoplasmic molecular markers

The genus Limonium, due to the patchiness of the natural habitats of its species as well as the high frequency of hybridization and polyploidy and the possibility of reproduction by apomixis, provides an example of all the principal mechanisms of rapid speciation of plants. As an initial study of evolution in this genus, we have analyzed intra- and interspecific variability in 17 species from section Limonium, the largest in the genus, based on RFLPs of cpDNA and nuclear rDNA ITS sequences. In the cpDNA analysis, 21 restriction enzymes were used, resulting in 779 fragments, 490 of which were variable and 339 parsimony informative. L. furfuraceum exhibited two relatively divergent cpDNA haplotypes. The relationships found among the species based on cpDNA restriction fragments were coincident using different methods of phylogenetic analysis. Due to the presumed reticulate evolution in the genus Limonium, the comparison of these results with data from the nuclear DNA was necessary; ITS sequences were analyzed. The final alignment contained 488 characters, of which 198 were variable and 156 parsimony informative. Two relatively divergent ITS types were present at the intraindividual level in L. delicatulum, a triploid species. Each type was related to ITS from different groups of diploid Limonium species, one with a base haploid chromosome number n = 8 (represented by L. cossonianum) and the other with n = 9 (represented by L. minutum). The different phylogenetic inference methods used for the analysis of ITS sequences rendered very similar topologies. In general, the relationships among the species studied were coincident with those obtained with the chloroplast genome. Both nuclear and cytoplasmic markers support the polyphyly of section Limonium, with at least two species, L. narbonense and L. vulgare, clearly divergent from the rest. Moreover, the remaining subsections into which section Limonium is currently divided seem to be artificial.     

Chromosome numbers of Panamanian Lecythidaceae and their use in subfamilial classification

Nine species of Lecythidaceae subfamily Lecythidoideae in four genera whose chromosome numbers were previously unknown, have 17 as their basic chromosome number:Eschweilera pittieri, three other unidentified species ofEschweilera, Grias cauliflora, Gustavia dubia, G. superba, Lecythis minor, andL. tuyrana. All are diploid exceptGustavia superba, which is tetraploid.Couroupita guianensis, which was previously—and probably incorrectly—reported to have a gametic chromosome number of 18, also hasn = 17. The known chromosome numbers support recognizing at least three of Niedenzu’s subfamilies: Planchonioideae withx = 13, Napoleonaeoideae withx = 16, and Lecythidoideae withx = 17. His fourth subfamily, Foetidioideae, with one genus of five species, has not been counted. Cytological data have been and probably will be useful in indicating to what subfamily problematic genera belong and in showing interesting phytogeographic patterns within the family. On the other hand, cytological data provide no recognizable clues relating the Lecythidaceae to other families.     

23种伞形科植物果实形态及其分类学意义

该实验采用徒手切片法对伞形科17属23种植物的果实进行了外部形态和解剖特征的观察,结果表明:伞形科果实有背腹压扁、两侧压扁和不压扁3种类型;侧棱有宽、有窄;油管的分布有棱槽单油管型和棱槽多油管型;花柱基多数为圆锥状,少数种的花柱基为扁平垫状;萼齿明显或不明显。通过进一步对属间和属内果实解剖特征的比较得出:(1)果实表面被钩刺或刚毛及果棱特征在属间差异明显,在属内表现出一致性,可作为伞形科属间分类的依据。(2)果实横切面的形状、胚乳腹面的凹凸以及萼齿的形态特征在属内种间的分类研究中有重要的意义。基于果实形态特征,编制了17属23种植物的分种检索表。     

Molecular Systematics and Evolution of Arabidopsis and Arabis

Abstract: We provide a phylogenetic analysis of the genera Arabidopsis and Arabis based on nuclear ribosomal DNA sequences. We show that traditional taxonomical concepts within tribe Ara-bideae, which includes these genera, are highly artificial. Arabis and Arabidopsis are paraphyletic and consist of several different independent lineages. The genus Capsella, originally placed in tribe Lepideae, is related to North American Arabis and the Arabidopsis thaliana lineage. Other genera, including East Asian Yin-shania, North American Halimolobus, cosmopolitan Barbarea and Cardamine, and European Aubrieta are positioned among different Arabis lineages. One Arabis species, Arabis pauciflora, is only distantly related to tribe Arabideae. Base chromosome number reduction from n = 8 to n = 5 to 7 occurred several times, suggesting that lower base chromosome numbers than n = 8 are derived in tribe Arabideae. Current knowledge on the evolution and systematics of the genera Arabis and Arabidopsis and relationships within the mustard family are summarized and discussed in the light of convergent evolution and transfer of knowledge from Arabidopsis thaliana as a molecular model plant to other species of the Cruciferae.     

Comparative karyotype analysis and chromosome evolution in the genus Aplastodiscus (Cophomantini, Hylinae, Hylidae)

ABSTRACT: BACKGROUND: The frogs of the Tribe Cophomantini present, in general, 2n?=?24 karyotype, but data on Aplastodiscus showed variation in diploid number from 2n?=?24 to 2n?=?18. Five species were karyotyped, one of them for the first time, using conventional and molecular cytogenetic techniques, with the aim to perform a comprehensive comparative analysis towards the understanding of chromosome evolution in light of the phylogeny. RESULTS: Aplastodiscus perviridis showed 2n?=?24, A. arildae and A. eugenioi, 2n?=?22, A. callipygius, 2n?=?20, and A. leucopygius, 2n?=?18. In the metaphase I cells of two species only bivalents occurred, whereas in A. arildae, A. callipygius, and A. leucopygius one tetravalent was also observed besides the bivalents. BrdU incorporation produced replication bands especially in the largest chromosomes, and a relatively good banding correspondence was noticed among some of them. Silver impregnation and FISH with an rDNA probe identified a single NOR pair: the 11 in A. perviridis and A. arildae; the 6 in A. eugenioi; and the 9 in A. callipygius and A. leucopygius. C-banding showed a predominantly centromeric distribution of the heterochromatin, and in one of the species distinct molecular composition was revealed by CMA3. The telomeric probe hybridised all chromosome ends and additionally disclosed the presence of telomere-like sequences in centromeric regions of three species. CONCLUSIONS: Based on the hypothesis of 2n?=?24 ancestral karyotype for Aplastodiscus, and considering the karyotype differences and similarities, two evolutionary pathways through fusion events were suggested. One of them corresponded to the reduction of 2n?=?24 to 22, and the other, the reduction of 2n?=?24 to 20, and subsequently to 18. Regarding the NOR, two conditions were recognised: plesiomorphy, represented by the homeologous small-sized NOR-bearing pairs, and derivation, represented by the NOR in a medium-sized pair. In spite of the apparent uniformity of C-banding patterns, heterogeneity in the molecular composition of some repetitive regions was revealed by CMA3 staining and by interstitial telomeric labelling. The meiotic tetravalent might be due to minute reciprocal translocations or to non-chiasmatic ectopic pairing between terminal repetitive sequences. The comparative cytogenetic analysis allowed to outline the chromosome evolution and contributed to enlighten the relationships within the genus Aplastodiscus.     

Karyomorphology of four species in Ancylostemon,Briggsiopsis and Lysionotus (Gesneriaceae)

Reported in the present paper are chromosome numbers and karyotypes of three genera of the Gesneriaceae, i.e. Ancylostemon Craib. , Briggsiopsis (Franch.) K. Y. Pan and Lysionotus D. Don. The former two genera are endemic to China. The karyotype of Ancylostemon aureus (Franch.) Burtt is formulated as 2n = 34 = 20m(1sat) + 14sm, with the same chromosome number as its allied species A. convexus Craib. This species is characterized by the interphase nucleus of complex chromocenter type and the proximal type of chromosomes in the mitotic prophase. The chromosome number of the monospecific genus Briggsiopsis is 2n = 34, the same as the lowest chromosome number reported in Briggsia. The karyotype of Briggsiopsis, which is formulated as 2n = 25m + 6sm + 3st, also seems to be primitive among the species of the two genera. Briggsiopsis is characterized by the interphase nucleus of simple-complex chromocenter type and the interstitial-gradient type of chromosomes in the mitotic prophase. The chromosome number of Lysionotus carnosus Hemsl. is the lowest reported in this genus. Its karyotype is formulated as 2n= 30 = 21m + 5sm + 3st + lt. Lysionotus serratus var. pterocaulis, with the karyotype being formulated as 2n= 32 = 2lm + 10sm + lt, has the same chromosome number as var. serratus. These two species show a remarkable differentiation of karyotypes and are characterized by the interphase nuclei of simple-complex chromocenter type and the gradient type of chromosomes in the mitotic prophase. _ .     

Chromosome studies in southern species of Mimosa (Fabaceae,Mimosoideae) and their taxonomic and evolutionary inferences

In this work, chromosome numbers and karyotype parameters of 36 taxa of the genus Mimosa were studied, especially from the southern South America center of diversification. Results support that x = 13 is the basic chromosome number in the genus. Polyploidy is very frequent, ca. 56 % of the total of the studied species here are polyploid, confirming that polyploids are more frequent at higher latitudes. The most common ploidy levels found are 2x and 4x, but some species studied exhibit 6x and 8x. In different groups, several ploidy levels were found. Parameters of chromosome size show statistically significant differences between close species, and asymmetry index A ₂ exhibited low variation between them. It is possible to infer variations of chromosome size between diploids and tetraploids and between basal and derived taxa. The present studies confirm or reveal polyploidy in several groups of South America which are highly diversified in the southernmost area of distribution of the genus, such as sect. Batocaulon ser. Stipellares and sect. Calothamnos. Our data are discussed in a taxonomic context, making inferences about the origin of some polyploid taxa. Polyploidy could be an important phenomenon that increases the morphologic diversity and specific richness in southern South America. On basis of our data, it is possible to hypothesize hybridization between same-ploidy level or different ploidy level taxa. As already shown in the literature, our results confirm the importance of the polyploidy in the speciation of the genus.