A CYTOTAXOXOMIC SURVEY OF MELAMPODIUM (COMPOSITAE-HELIANTHEAE)

Turner , B. L.. and R. M. King . (U. Texas, Austin.) A cytotaxonomic survey of Melampodium (Compositae-Heliantheae). Amer. Jour. Bot. 49(3): 233–26. Illus. 1962.—Chromosome counts are reported for individuals from 89 populations of Melampodium representing 26 species The genus is multibasic with x = 9, 10, 11, 12, 16 and 23. Chromosome numbers on a base of x = 10 characterize the section Melampodium while basic numbers of x = 23, 16, 12, 11 and 9 occur in the section Zarabellia. Melampodium camphoratum (n = 16) differs from all other species examined in having relatively small meiotic chromosomes. Only 6 of the 23 species are polyploid or have polyploid races. Melampodium leucanthum and M. cinereum have both diploid and tetraploid populations; the latter occur without any apparent morphological or geographical correlation and are probably autoploid in origin. A survey of the basic chromosome numbers known for other genera of the subtribe Melampodinae (12 of 22 genera) is presented. and it is suggested that x = 10 is the most probable basic number of the genus and subtribe.     

Molecular phylogenetic analyses of nuclear and plastid DNA sequences support dysploid and polyploid chromosome number changes and reticulate evolution in the diversification of Melampodium (Millerieae, Asteraceae)

Chromosome evolution (including polyploidy, dysploidy, and structural changes) as well as hybridization and introgression are recognized as important aspects in plant speciation. A suitable group for investigating the evolutionary role of chromosome number changes and reticulation is the medium-sized genus Melampodium (Millerieae, Asteraceae), which contains several chromosome base numbers (x = 9, 10, 11, 12, 14) and a number of polyploid species, including putative allopolyploids. A molecular phylogenetic analysis employing both nuclear (ITS) and plastid (matK) DNA sequences, and including all species of the genus, suggests that chromosome base numbers are predictive of evolutionary lineages within Melampodium. Dysploidy, therefore, has clearly been important during evolution of the group. Reticulate evolution is evident with allopolyploids, which prevail over autopolyploids and several of which are confirmed here for the first time, and also (but less often) on the diploid level. Within sect. Melampodium, the complex pattern of bifurcating phylogenetic structure among diploid taxa overlain by reticulate relationships from allopolyploids has non-trivial implications for intrasectional classification.     

CHROMOSOME NUMBERS IN THE COMPOSITAE. X. NORTH AMERICAN SPECIES

Chromosome counts from 132 plant populations representing 124 taxa (in 67 genera) are reported. These include previously unreported counts for over 70 species and 5 new generic counts (Hofmeisteria, x = 19; Oxypappus, x = 10; Pterocaulon, x = 10; Stenocarpha, x = 8; and Urbinella, x = 8). Two new base numbers are reported for specieis of Perityle (P. californica, x = 13 and P. palmeri, x = 17), and previously unreported n numbers have been found for species of the genera Bidens (n = 17) and Hymenostephium (n = 21). Several gametic cells with differing meiotic configurations were found in the same head of Stevia viscida (n = 11 pairs; 11 pairs and 11 univalents; 33 univalents). When appropriate, the chromosomal information has been related to systematic problems, especially for genera of the subtribes Flaverinae, Coreopsidinae, Galinsoginae and Peritylinae.     

Chromosome numbers and generic relationships in subtribe Stephanomeriinae (Compositae: Ichorieae)

Chromosome numbers are reported from over 230 populations representing species in eight genera. First counts are reported for three species ofStephanomeria, five species ofLygodesmia, and one species ofPinaropappus. Base chromosome numbers,x = 6, 7, 8, and 9 are known in the subtribe;x = 9 is found in six of the 12 genera and presumably is the ancestral base number for the subtribe. Two phyletic lines, aMalacothrix line and aStephanomeria line are recognized on morphological grounds. A key to the 12 genera is provided.     

Molecular Phylogeny of Eupatorieae (Asteraceae) Estimated from cpDNA RFLP and its Implication for the Polyploid Origin Hypothesis of the Tribe

Neomirandea (x=17 and 25), Ageratina (x=17) and Sclerolepis (x=15) with the higher chromosome base numbers, and the other includes Mikania (x=17) and the remaining genera with lower chromosome base numbers (x=10–11). However, the monophyly of the former clade is supported with a low bootstrap value. In the latter clade, Mikania (x=17) diverged first, then Stevia (x=11), and finally eight genera with x=10 diverged in succession. This result supports the hypothesis that the genera in the tribe Eupatorieae with x =10 evolved from an ancestor with a higher base number, and the tribe is of polyploid origin. Received 13 September 1999/ Accepted in revised form 20 January 2000     

Cytotaxonomy of the apocynaceae

At present there is karyological information on ca 10% of the species and ca 30% of the genera of the Apocynaceae. Basic numbers of x = 6, 8, 9, 10, 11, 12, 16, 18, 20, 21 and 23 have been assessed. Of these x = 11 is primitive, occurring in ca 60% of the genera. Those of x = 6, 8, 9 and 10 have evolved by reduction, and x = 12 by increase from x = 11. In the subtribe Secondatiinae however, x = 12 is most likely the result of doubling x = 6. The numbers x = 16, 18 and 20 are likewise doubles of x = 8, 9 and 10 respectively. Those of x = 21, 23, and in one case, x = 20 are probably aneuploid products of doubles of x = 11. The two larger subfamilies, Plumerioideae and Apocynoideae have the basic numbers x = 8, 9, 10 and 11 in common and are not separable on the basis of chromosomal evidence. The third small subfamily Cerberoideae is more homogeneous according to basic number, i.e. x = 10 and 20. Most genera are characterized by a constant basic number, but some have two basic numbers; these clearly are cases of infrageneric aneuploidy. Based on records in the literature two closely related generaApocynum andTrachomitum appear to be characterized by a basic number of x = 8 as well as x = 11. This conflicting situation should be clarified by further karyological research. From the level of subtribe onwards some taxa have one basic number, but others are characterized by two or more numbers. The occurrence of similar basic numbers in different phylads of the family is considered to be the result of similar chromosomal evolution mechanisms. Approximately 22% of the investigated species are polyploid. Intrageneric polyploidy occurs with a frequency of about 12.5% and infraspecific polyploidy with less than 4%. The karyotypes observed are symmetrical: the chromosomes within a karyotype are similar in length with primary constrictions usually in a median position. In the Tabernaemontaneae however, it was observed that the karyotypes comprise one pair of distinctly heterobrachial chromosomes in addition to the metacentric ones. This tribe is also characterized by chromosomes which are relatively long. Most genera of the African continent, which are well known regarding their chromosome number, are characterized by x = 11. Exceptions areStrophantus (x = 9) with a mainly tropical African distribution. Two other genera with derived numbers, i.e.Gonioma with x = 10 andPachypodium with x = 9, occur in southern Africa and Madagascar. The genera with a non-African distribution are less known for their chromosome number. However, the available evidence suggests that evolution of derived numbers has occurred more frequently outside Africa than on this continent.     

天门冬科黄精族细胞学研究进展

在全面收集和整理黄精族染色体数据的基础上,对国内外有关黄精族各类群间的染色体数目和倍性的变化规律进行了总结,并从染色体的多倍化和非整倍化与系统发育关系和地理分布方面探讨了黄精族内各属的起源和演化关系问题。黄精族包括黄精属、舞鹤草属、异黄精属和竹根七属,共约100余种,其中舞鹤草属(x=18)、异黄精属(x=16)和竹根七属(x=20)的染色体基数稳定,而黄精属染色体基数波动较大,主要为x=8~16,既有多倍化也有非整倍化现象。染色体数据表明黄精族4个属的染色体进化模式各不相同,揭示了黄精族内染色体从高基数向低基数演化的规律;各属内染色体的演化主要是体现在二倍体水平上的核型变异,多倍化在本族中不占主导地位;仅黄精属内伴有非常强烈的非整倍化现象;细胞学证据与分子系统发育的结果比较吻合,为黄精族内属间以及属下的系统发育与进化提供了重要的参考资料。     

Karyomorphology and relationships in some genera of Saururaceae and piperaceae

Karyomorphological observations were carried out on three genera belonging to the Saururaceae and four genera of the Piperacea. All of the genera of Saururaceae show the same karyomorphological characteristics from interphase to metaphase in the somatic cell divisions. However there are two types of the karyomorphology in Piperaceae, i) the first type observed inPiper, Pothomorphe andZippelia, and ii) the second type inPeperomia. Each group corresponds to Thorne's two subfamilies (1974, 1976), Piperoideae and Peperomioideae. The basic chromosome numbers of the genera are confirmed or newly proposed as follows:Saururus x=11,Houttuynia x=12,Anemopsis x=22 (Saururaceae),Peperomia x=11,Piper andPothomorphe (=Heckeria) x=13,Zippelia x=19 (Piperaceae). The relationships of these basic chromosome numbers are presumed to be as shown schematically in Fig. 4. The original basic chromosome number of the common ancestral stock of Saururaceae and Piperaceae is presumed to be x=11.     

First report of chromosome numbers of the Carlemanniaceae (Lamiales)

The Carlemanniaceae comprises two small genera that are restricted to East Asia: the Carlemannia and Silvianthus. These genera were previously placed in the Rubiaceae or Caprifoliaceae, but are now considered a distinct family that is probably related to the Oleaceae in the Lamiales. The family is still poorly understood with respect to its morphological characteristics. Here, we present the first report of the chromosome numbers of the family using species from both genera, i.e., Carlemannia tetragona, Silvianthus bracteatus ssp. bracteatus, and S. bracteatus ssp. clerodendroides. The species were compared with the chromosome numbers of Oleaceae and associated families using a Bayesian tree that was generated from rbcL and ndhF sequence data from Genbank. C. tetragona had 2n = 30 (x = 15), whereas the two subspecies of Silvianthus had 2n = 38 (x = 19). Comparisons of chromosome numbers support the distinctness of the Carlemanniaceae, not only from the Oleaceae (x = 11, 13, 23), but also from the Tetrachondraceae (x = 10, 11), a family that is possibly related to the Carlemanniaceae and/or Oleaceae in the Lamiales. The notable difference in chromosome number between Carlemannia and Silvianthus, as well as the differences in other characteristics (pollen, seed, and fruit morphology), suggests that the family split early in its evolution.     

Evolutionary trends in Iridaceae: new cytogenetic findings from the New World

With the present work, we aim to provide a better understanding of chromosome evolutionary trends among southern Brazilian species of Iridoideae. Chromosome numbers and genome sizes were determined for 21 and 22 species belonging to eight genera of Tigridieae and two genera of Trimezieae, respectively. The chromosome numbers of nine species belonging to five genera are reported here for the first time. Analyses of meiotic behaviour, tetrad normality and pollen viability in 14 species revealed regular meiosis and high meiotic indexes and pollen viability (> 90%). The chromosome data obtained here and compiled from the literature were plotted onto a phylogenetic framework to identify major events of chromosome rearrangements across the phylogenetic tree of Iridoideae. Following this approach, we propose that the ancestral base chromosome number for Iridoideae is x = 8 and that polyploidy and dysploidy events have occurred throughout evolution. Despite the variation in chromosome numbers observed in Tigridieae and Trimezieae, for these two tribes our data provide support for an ancestral base number of x = 7, largely conserved in Tigridieae, but a polyploidy event may have occurred prior to the diversification of Trimezieae, giving rise to a base number of x₂ = 14 (detected by maximum‐parsimony using haploid number and maximum likelihood). In Tigridieae, polyploid cytotypes were commonly observed (2x, 4x, 6x and 8x), whereas in Trimezieae, dysploidy seems to have been the most important event. This feature is reflected in the genome size, which varied greatly among species of Iridoideae, 4.2‐fold in Tigridieae and 1.5‐fold in Trimezieae. Although no clear difference was observed among the genome sizes of Tigridieae and Trimezieae, an important distinction was observed between these two tribes and Sisyrinchieae, with the latter possessing the smallest genome sizes in Iridoideae. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 177 , 27–49.     

First report of chromosome numbers and karyotypes of two monotypic genera endemic to eastern Asia: Brachystemma (Caryophyllaceae) and Craspedolobium (Fabaceae)

The chromosome numbers and karyotypes of Brachystemma and Craspedolobium, two monotypic genera endemic to eastern Asia, are reported here for the first time. The somatic chromosome numbers are 2n=40 for Brachystemma calycinum and 2n=22 for Craspedolobium unijugum. A karyotype of 2n=2x=40=28m+12sm was found in B. calycinum and that of 2n=2x=22=12m+10sm in C. unijugum, both of them have a moderately symmetrical karyotype type 2B and small‐sized chromosomes. Brachystemma has a unique basic chromosome number in Alsinoideae, which may support its isolated taxonomic position. As do some morphological characters, the basic chromosome number x=11 suggests that Craspedolobium belongs in the Millettioid clade.     

Chromosome evolution in the Laurales based on analyses of original and published data

We present a summary of currently available chromosome information for all seven families in the order Laurales on the basis of original and previously published data and discuss the evolution of chromosomes in this order. Based on a total of 53 genera for which chromosome data were available, basic chromosome numbers appear consistent within families: x = 11 (Calycanthaceae); x = 22 (Atherospermataceae and Siparunaceae); x = 19 (Monimiaceae); and x = 12 and 15 (Lauraceae). The Hernandiaceae have diverse numbers: x = 15 (Gyrocarpoideae) and x = 18 and 20 (Hernandioideae). Karyotype analyses showed that Hennecartia, Kibaropsis, and Matthaea (all Monimiaceae) contained two or three sets of four distinct chromosomes in 38 somatic chromosomes, suggesting that 2n = 38 was derived by aneuploid reduction from 2n = 40, a tetraploid of x = 10. In light of the overall framework of phylogenetic relationships in the Laurales, we show that x = 11 is an archaic base number in the order and is retained in the Calycanthaceae, which are sister to the remainder of the order. Polyploidization appears to have occurred from x = 11 to x = 22 in a common clade of the Siparunaceae, Atherospermataceae, and Gomortegaceae (although 2n = 42 in the Gomortegaceae), and aneuploid reduction from x = 11 to x = 10 occurred in a common clade of the Hernandiaceae, Lauraceae, and Monimiaceae. To understand chromosome evolution in the Lauraceae, however, more studies are needed of genera and species of Cryptocaryeae.     

Another perspective on cytoevolution in Lobelioideae (Campanulaceae)

The Lobelioideae is a cosmopolitan group whose cytoevolution is discussed on a model of primitively high diploid chromosome numbers, in which x = 14 is relatively plesiomorphic and x = 21 may be even more plesiomorphic. This model is suggested from the high frequency of lobelioid genera with x = 14, the probably plesiomorphic condition of x = 17 in the sister group Campanuloideae (Campanulaceae), and the primitive x = 15 in Stylidiaceae (Campanulales). It contrasts with that for a primitive x = 7 and paleopolyploidy to higher chromosome numbers. In our analysis, the genus Lobelia shows three broad cytoevolutionary groups, which probably have phylogenetic and infrageneric taxonomic significance: (1) woody diploids with x = 21 in Chile and woody diploids with x = 14 in Africa, Asia, and Hawaii; (2) herbaceous diploids with several series of dysploid chromosome numbers n = 19, 13, 12, 11, 10, 9, 8, 7, 6, mainly in Africa and Australia; (3) widespread and speciose herbaceous taxa based on a very derived n = 7, with recent frequent euploid rises (neopolyploidy) at or below the species level in subgenus Lobelia and allied or segregate genera. Other woody and herbaceous lobeliad genera have comparable cytoevolutionary patterns. New chromosome counts for Australian Lobelia, Pratia, and Isotoma illustrate the last two cytoevolutionary groups.     

CHROMOSOME NUMBERS IN THE COMPOSITAE: COLOMBIAN SPECIES

Chromosome numbers are presented for 76 species belonging to 35 genera of Compositae from Colombia. Thirty-nine species and three genera, Espeletia (x = 19), Steiractinia (x = 14), and Vasquezia (x = 19), are reported for the first time. New base numbers or chromosome series are recorded in Baccharis (B. nitida, n = 25), Calea (C. caracasana, n = 24), and Liabum (L. mega-cephalum, n = 10).     

CHROMOSOME NUMBERS IN THE COMPOSITAE. XIV. LACTUCEAE

Reports of 150 original chromosome counts are recorded, including reports of 22 genera and 57 species and subspecific taxa in tribe Lactuceae. Also included are first reports for 12 specific or subspecific taxa. x = 9 appears to be the ancestral base of the tribe. Chromosome numbers are known for over 85% of the genera of the tribe and the frequency of polyploidy is ca. 23%, which is about one-half that of the angiosperms.     

Cytoevolutionary patterns inRutaceae

Chromosome numbers for 9 tribes and 73 genera ofRutaceae are examined for the probable chromosome base numbers in these taxa. There is abundant dysploidy and infrageneric polyploidy in the largeRutoideae/Toddalioideae complex. We found that x = 18 was typical for the tribesZanthoxyleae andToddalieae; probably ancestral in theBoronieae and perhaps in theRuteae, Diosmieae, andCusparieae; and characteristic of subfamilyFlindersioideae. Considering the basic position of elements ofZanthoxyleae andToddalieae in the family it appears that diploid x = 18 is ancestral in theRutaceae. The morphologically advancedCitroideae are invariant for x = 9 and may be a product of dysploid reduction.     

CHROMOSOME NUMBERS IN THE COMPOSITAE. XII. AUSTRALIAN SPECIES

Chromosome counts are reported for plants from 171 populations of Australian Compositae; most of these are first reports for the approximately 104 taxa distributed among 37 genera. New generic counts with base numbers indicated include: Astereae —Bellida (x = 9), Minuria (x = 9); Inuleae —Angianthus (x = 12, 13), Calocephalus (x = 7), Cephalipterum (x = 12, 14), Craspedia (x = 11), Gnaphalodes (x = 10), Gnephosis (x = 4, 12), Myriocephalus (x = 6), Isoetopsis (x = 17); Calenduleae —Tripteris (x = 8); and Artcoideae —Arctotheca (x = 9). Most of the counts were from the tribes Astereae (47) and Inuleae (95). The phyletic import of these data is discussed selectively and comparisons are made with the chromosomal variation found in the Australian desert Compositae with that found in the North American desert Compositae.     

Cladistical analysis of primitive G-band sequences for the karyotype of the ancestor of the Cricetidae complex of rodents

Homologous segments identified by G-banding sequences of chromosomes of Peromyscus boylii, Neotoma micropus, Oryzomys capito, (Family Cricetidae) Rattus norvegicus, Melomys burtoni, and Apodemus sylvaticus (Family Muridae) were used to hypothesize a chromosomal condition for the cricetid ancestor. A critical assumption in proposing the primitive G-banding sequences for a given chromosome is that if the outgroup and ingroup taxa have a specific sequence, then the ancestor of the ingroup taxa also had that same sequence. Using this methodology, (chromosome numbers refer to proposed homology to the standardized karyotype for Peromyscus), we propose that: (1) the primitive banding pattern of chromosome 1 was identical to that of Neotoma; (2) the primitive patterns of chromosomes 2, 3, 4, 6, 7, 8, 9, 10, 11, and 12 were primitive banding patterns of 5 and 13 were undetermined; (4) a major portion of the banding patterns of 14 and X were present in the ancestral karyotype. Only the largest 14 autosomes and X were examined because the smaller elements had insufficient G-band definition to ensure reasonable accuracy. The karyotype ancestral to that of Peromyscus, Neotoma, and Oryzomys may be as above and the banding patterns of 5, 13, and 14 were acrocentric and identical to those shown for Peromyscus, Neotoma, and Oryzomys (Fig. 1). In the primitive karyotype, heterochromatin (C-band material) was probably limited to the centromeric regions. If the primitive karyotype is as described above, then it is possible to determine the direction, type, and magnitude of chromosomal evolution evident in the various cricetid lineages. Based on the available data, radiation from the ancestral cytotype is characterized by a nonrandom distribution of types of chromosomal changes. Within many genera, more rearrangements occur in the 14 largest autosomal chromosomes of some congeneric species than distinguish the proposed primitive conditions for the genera Peromyscus, Neotoma, and Oryzomys. It would appear that the extensive morphological radiation from the primitive cricetid ancestor as indicated by the presence of over 100 surviving genera within the family, was not accompanied by extensive karyotypic changes. The magnitude of chromosomal variation that accompanies speciation in these genera appears to range from no detectable chromosomal evolution to a radical reorganization of the genome.     

Maximum likelihood inference implies a high, not a low, ancestral haploid chromosome number in Araceae, with a critique of the bias introduced by 'x'

Background and Aims

For 84 years, botanists have relied on calculating the highest common factor for series of haploid chromosome numbers to arrive at a so-called basic number, x. This was done without consistent (reproducible) reference to species relationships and frequencies of different numbers in a clade. Likelihood models that treat polyploidy, chromosome fusion and fission as events with particular probabilities now allow reconstruction of ancestral chromosome numbers in an explicit framework. We have used a modelling approach to reconstruct chromosome number change in the large monocot family Araceae and to test earlier hypotheses about basic numbers in the family.

Methods

Using a maximum likelihood approach and chromosome counts for 26 % of the 3300 species of Araceae and representative numbers for each of the other 13 families of Alismatales, polyploidization events and single chromosome changes were inferred on a genus-level phylogenetic tree for 113 of the 117 genera of Araceae.

Key Results

The previously inferred basic numbers x = 14 and x = 7 are rejected. Instead, maximum likelihood optimization revealed an ancestral haploid chromosome number of n = 16, Bayesian inference of n = 18. Chromosome fusion (loss) is the predominant inferred event, whereas polyploidization events occurred less frequently and mainly towards the tips of the tree.

Conclusions

The bias towards low basic numbers (x) introduced by the algebraic approach to inferring chromosome number changes, prevalent among botanists, may have contributed to an unrealistic picture of ancestral chromosome numbers in many plant clades. The availability of robust quantitative methods for reconstructing ancestral chromosome numbers on molecular phylogenetic trees (with or without branch length information), with confidence statistics, makes the calculation of x an obsolete approach, at least when applied to large clades.