Chromosome numbers in plant taxa endemic to the Balearic Islands

Mitotic chromosome numbers are reported from 20 vascular plant taxa that are endemic to the Balearic Islands and poorly known cytogenetically. The chromosome numbers of Arenaria grandiflora L. ssp. glabrescens (Willk.) G. López & Nieto Feliner (2 n  = 44), Dianthus rupicola Viv. ssp. bocchoriana L. Llorens & Gradaille (2 n  = 30), Solenopsis minuta (L.) C. Presl. ssp. balearica (E. Wimm.) Meikle (2 n  = 28), Romulea asumptionis Font Quer & Garcías Font (2 n  = 56), Scutellaria balearica Barceló (2 n  = 22) and Galium balearicum Briq. (2 n  = 22) have been determined for the first time. A new chromosome number was found in two populations of Helictotrichon crassifolium (Font Quer) Holub (2 n  =  c. 98) suggesting that this species is a high polyploid (14 x ), in contrast to an earlier report of a lower chromosome count (2 n  = 12 x  = 84). Cytogenetic observations suggest that Naufraga balearica Constance & Cannon has a diploid chromosome complement of 2 n  = 20, with 0–2 accessory chromosomes. The banded karyotype (chromomycin A₃) of Crepis triasii (Cambess.) Fries was determined for individuals belonging to eight populations from three islands. Two chromomycin A₃-positive regions were recorded in the diploid complement. These are present on the telomeric regions of the shortest subtelocentric chromosomes. This species is karyologically stable in chromosome number, karyotype and fluorochrome-banding pattern among populations from separate islands.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 148 , 219–228.     

Cytogenetics of species of Chamaecrista (Leguminosae – Caesalpinioideae) native to southern Brazil

Chromosome numbers, karyotypes, meiotic behaviour and pollen analysis are presented for species of Chamaecrista Moench (Leguminosae, Caesalpinioideae, Cassieae ) native to southern Brazil: C. nictitans ssp. patellaria , C. nictitans ssp. disadena , C. repens , C. rotundifolia , C. flexuosa , C. vestita and C. desvauxii . Meiotic behaviour is reported for the first time for all the taxa and was very regular; only bivalents were formed at diakinesis and metaphase I, chromosome disjunction and segregation were regular at anaphases I and II, meiotic indexes were over 99% and pollen fertility was over 92%. Pollen grains were subprolate in C. flexuosa and C. vestita and prolate–spheroidal in the other taxa. Karyotypes were symmetrical in all six species and the data are original, except for C. nictitans ssp. p atellaria. Chromosome number is presented for the first time for C. repens (2 n  = 16) and has been confirmed for the other taxa: 2 n  = 14 for C. desvauxii , 2 n  = 32 for the tetraploid C. nictitans ssp. patellaria and C. nictitans ssp. disadena , and 2 n  = 16 for the other species. These two basic numbers found in the genus, x  = 7 and x  = 8, point to chromosome evolution by dysploidy, which has also been accompanied by polyploidy.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 429–439.     

Cytotypes of Andropogon gerardii Vitman (Poaceae): fertility and reproduction of aneuploids

In many North American prairies, populations of Andropogon gerardii Vitman (Poaceae) are composed of hexaploid and enneaploid cytotypes (2 n  = 60, 90), with intermediates occurring occasionally. Under controlled pollination, the two common cytotypes can be crossed, producing progeny with a range of chromosome numbers. In an investigation of fertility and compatibilities of intermediate cytotypes, individuals with chromosome numbers between 60 and 90 were crossed with each other, with the 2 n  = 60 and 90 cytotypes, and with South American Andropogon species having 60 chromosomes. Regardless of cytotype, all A. gerardii plants had some fertility and virtually all crosses produced seeds. Cytotype is only partially predictive of fertility. Inter-specific hybrids between A. gerardii and South American hexaploid species were vigorous but sterile. Gene flow in natural A. gerardii populations of mixed cytotype probably involves plants of all cytotypes.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 141 , 95–103.     

A review of ploidy in the genus Prosopis (Leguminosae)

The genus Prosopis contains 44 species of trees and shrubs, the majority of which originate in the Americas. Most species are reported to be diploid, with a somatic chromosome number of 2 n  = 28. There are rare reports of polyploidy, although it is thought that these may represent polysomaty in root tissues. However, flow cytometry has recently indicated that P. juliflora is entirely tetraploid with a somatic chromosome number of 2 n  = 56. In order to clarify the situation, an extensive review of ploidy in Prosopis was undertaken, the first of its kind. The ploidy levels of 124 samples of Prosopis from 21 countries, including both the natural and introduced ranges, were analysed using flow cytometry. In addition, a comprehensive literature review was carried out, examining 305 published ploidy values and covering 32 of the 44 species of Prosopis . Flow cytometry analysis suggests that P. juliflora is the only tetraploid species, with a somatic chromosome number of 2 n  = 4 x  = 56, whilst the remainder of the species analysed are diploid with 2 n  = 2 x  = 28, including the first report for P. articulata (2 n  = 28). A critical review of published ploidy values shows that all species of Prosopis are reported to be entirely diploid, except P. glandulosa , P. juliflora , and P. koelziana , for which both diploid and tetraploid values have been recorded. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 425–438.     

Occurrence of tetraploid and octoploid cytotypes in Senecio jacobaea ssp. jacobaea (Asteraceae) in Pannonia and the Carpathians

Four different cytotypes have been reported for Senecio jacobaea L. ssp. jacobaea throughout Europe, with the most common occurrence of tetraploids (2 n  = 40). Here we present a survey of previously published chromosome number data on this subspecies and its geographical distribution, and focus on populations from Pannonia and the Carpathians. Two ploidy levels have been determined in the study area, using chromosome counting and flow cytometry: tetraploid (2 n  = 40) and octoploid (2 n  = 80). Fifty-one populations originating from Slovakia, Austria, the Czech Republic, Hungary, Ukraine and Romania have been analysed. Multivariate morphometric analyses have been performed on 39 populations to study morphological differentiation between these two cytotypes. Despite slight morphological tendencies expressed on the level of populations, tetraploid and octoploids cannot be reliably distinguished morphologically and they are not taxonomically classified formally here.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 153 , 231–242.     

Determination of ploidy and nuclear DNA content in populations of Atriplex halimus (Chenopodiaceae)

Nuclear DNA contents were determined by flow cytometry for 20 populations of the perennial C₄ shrub Atriplex halimus L. (Chenopodiaceae) originating from the Mediterranean basin and Fuerteventura (Canary Islands). Two populations were also analysed for chromosome number: one (from Ibiza, Spain), with a 2C nuclear DNA content of 2.40 pg, was shown to be diploid (2 n  = 2 x  = 18), whilst the other (from Sicily, Italy), with 5.11 pg, was tetraploid (2 n  = 2 x  = 36). With respect to nuclear DNA content, two groups of populations were detected, diploids with 2.40–2.44 pg and tetraploids with 4.77–5.13 pg. The diploid populations were mainly from the western Mediterranean (Spain and France) and Fuerteventura, whereas tetraploids were generally, but not exclusively, from more arid areas in North Africa and the eastern Mediterranean. In general, the diploid and tetraploid populations corresponded to the subspecies halimus and schweinfurthii , respectively. For certain populations having morphologies intermediate between those considered typical of these two subspecies, nuclear DNA contents showed them to be tetraploid. There was significant variation in nuclear DNA content among the tetraploid populations, with greater values in the more easterly populations.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 147 , 441−448.     

Karyotype analysis in South American species of Myrtaceae

In Myrtaceae (Myrteae), the diploid chromosome number 2 n  = 2 x  = 22 is the most common, although variations of ploidy level occur, with some triploid (2 n  = 3 x  = 33) and tetraploid (2 n  = 4 x  = 44) records. Karyotype details in this group are scarce because the chromosomes are small (< 2 μm). In this work, we carried out a karyotypic analysis of 15 species of Myrtaceae grouped in different subtribes and genera. Measurements of chromosome length (long arm, L ; short arm, S ) were taken and several karyotypic parameters were calculated for each species. The karyotypes in fleshy-fruited taxa (Myrteae) were more varied than in the other previously analysed dry-fruited group ( Eucalyptus , Eucalypteae), in which the chromosomes were exclusively metacentric.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155 , 571–580.     

Karyological and taxonomic notes on Ophrys (Orchidoideae, Orchidaceae) from the Iberian Peninsula

Karyological information on Iberian Ophrys species is very limited. This paper provides the haploid and diploid chromosome numbers of 11 taxa of sect. Pseudophrys and sect. Ophrys , both of which are well represented in the Iberian Peninsula, and two taxa from Tunisia. The first data on chromosome numbers for O. vasconica (2 n  = 72, 74), O. ficalhoana (2 n  = 36), O. picta (2 n  = 36), O. sphegifera ( n  = 18, 2 n  = 36, 38) and O. passionis (2 n  = 36) are also presented, confirming the stability of the chromosome number in Ophrys . In addition, populations of the group O. omegaifera ( O. dyris and O. vasconica ), together with tetraploidy, pentaploidy and the existence of aneuploid phenomena, are reported for the first time in Iberia. The basic diploid number is always 2 n  = 36. The karyotypes of several species were analysed. Evolutionary trends in Ophrys chromosomes are discussed. Taxonomic and phytogeographical details are provided on several species or groups of species from Iberia.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003 , 142 , 395−406.     

Chromosome numbers and karyotypes of South American species and populations of Hypochaeris (Asteraceae)

One hundred and thirty-seven new chromosome counts are reported from 104 populations of 26 native South American taxa of Hypochaeris (Asteraceae, Lactuceae), together with two invasive Mediterranean species: H. glabra and H. radicata . First reports are provided for seven taxa ( H. alba , H. cf. eremophila , H. caespitosa , H. hookeri , H. parodii , H. patagonica and H. pinnatifida ) and one new ploidy level is reported (diploid for H. incana , so far known only as a tetraploid). Including the results of this study, the chromosomes of 39 of the c . 50 Hypochaeris species known from the New World have now been counted. Most species are diploid with 2 n  = 2 x  = 8 and have bimodal, asymmetrical karyotypes. Tetraploidy (2 n  = 4 x  = 16) is reported here for the first time in H. caespitosa . Infra-specific polyploidy (probably autopolyploidy) is reported in H. incana and H. taraxacoides , both cases including infra-populational cytotype mixtures (2 x and 4 x ). Polyploidy is now known from eight South American Hypochaeris species ( c . 16%). Basic karyotype analyses allow the placement of the newly counted taxa into previously proposed but slightly modified groupings and provide the framework for further molecular cytogenetic analyses. The reported findings suggest that chromosomal change in South American Hypochaeris , in contrast to Old World species, has not involved aneuploidy, but polyploidy and/or more subtle changes in chromosome length, perhaps via satellite DNA amplification/deletion or activity of retroelements, and rDNA reorganization.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 153 , 49–60.     

Hybrid origins of Ixeris nakazonei (Asteraceae, Lactuceae) in the Ryukyu Archipelago, Japan: evidence from molecular data

The proposed hybrid origin of Ixeris nakazonei collected in the Ryukyu Archipelago (Okinawajima) and the Atsumi Peninsula (Koijigahama) of central Japan was examined using nuclear DNA (nDNA) and chloroplast DNA (cpDNA) markers. The results indicated that most tetraploids of I. nakazonei (2 n  = 32) had nDNA of both putative parents, I. debilis (2 n  = 48) and I. repens (2 n  = 16). The first tetraploid of I. nakazonei must have arisen directly from interspecific hybridization between I. debilis and I. repens , considering the intermediacy of the chromosome number. All tetraploids on Okinawajima had cpDNA of I. repens , while those in the Atsumi Peninsula had cpDNA of I. debilis , indicating that the tetraploid has at least two independent origins. All hexaploids of I. nakazonei (2 n  = 48), on the other hand, had cpDNA of I. debilis , but some of the hexaploids had nDNA of both putative parents. Ixeris debilis and I. repens may also be involved in the origin of the hexaploid, although the establishment process of this cytotype is still obscure. Since the hexaploid of I. nakazonei is cytologically indistinguishable from I. debilis , it can backcross with I. debilis . Introgression from diploid I. repens to hexaploid I. debilis mediated by I. nakazonei possibly occurs on Okinawajima.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 141 , 379–387.     

Chromosomal variability in the genus Primula (Primulaceae)

Chromosome numbers and measurements were recorded in 47 individuals of ten taxa of Primula , representing eight species and two subspecies from ten populations. The basic numbers of chromosomes were x  = 8, 9 or 11, and they were mostly metacentric, medium-long to medium-small, ranging in length from c . 3.6 µm to 1.6 µm. Diploid chromosome numbers of 2 n  = 2 x  = 24 and 22 were scored for the first time in P. loeseneri Kitag. and P. prenantha Balf. & Sm., respectively. A new ploidy level of 2 n  = 4 x  = 44 was found in P. burmanica Balf. & King. The recorded diploid numbers of the remaining species confirmed earlier reports. Interspecific variability in chromosome numbers was correlated with heterogeneity in their mean length. Comparison of the data with those in the literature revealed that the observed variability of chromosomal characters was compatible with the other taxonomic criteria and supports the current taxonomic delimitation. Chromosomal variation at the diploid level is the predominant feature in Primula evolution, and allopatric speciation has played a major role in its specific diversity. Subgen. Aleuritia could represent the main clade from which the other subgenera have evolved. The origin of the chromosome numbers, geographical distribution and evolution of the species were assessed, and the parallel polyphyletic mode of evolution in the genus was confirmed.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 211–219.     

Chromosome counts in the genus Festuca section Eskia (Poaceae) in the Iberian Peninsula

Chromosome numbers of taxa of Festuca L. section Eskia Willk. in the Iberian Peninsula are given. The levels of ploidy for five taxa are confirmed. Idiograms and karyotypic formulae of the five taxa are presented for the first time. Two levels of ploidy occur in this section: diploid and tetraploid. One taxon, Festuca elegans ssp. merinoi is tetraploid and two other taxa have diploid and tetraploid populations. The remaining two taxa are solely diploid.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 331–337.     

Ploidal levels in the arctic-alpine polyploid Draba lactea (Brassicaceae) and its low-ploid relatives

Ploidal level information is of particular importance in intricate polyploid complexes such as in arctic-alpine Draba . Relative DNA content is reported for the tetra- and hexaploid D. lactea and seven of its low-ploid relatives. Flow cytometry was used to study 200 plants from 93 populations, the screening based on relative fluorescence. Absolute DNA content was determined by Feulgen densitometry for 13 plants from seven species, and reference chromosome numbers were determined in 12 plants (1–3 per species) representing six species. The plants grouped into diploids (2 n  = 16), tetraploids (2 n  = 32), hexaploids (2 n  = 48), and two triploids. Each ploidal level showed a linear increase in relative DNA content, pointing to a relatively recent polyploid origin. The diploid level was confirmed in D. nivalis, D. subcapitata, D. fladnizensis , and D. lonchocarpa. Draba palanderiana , reported previously as di-, tetra- and octoploid, was diploid in all investigated accessions. Hexa- and tetraploids were observed in D. lactea , in approximately the same ratio (8 : 1) as reported previously. The ploidal levels of the Central Asian D. altaica and D. turczaninovii are reported here for the first time as diploid and tetraploid, respectively.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 333–347.     

Karyotype evolution in the genus Boronia (Rutaceae)

New chromosome counts are reported for Boronia clavata 2 n  = 14, B. heterophylla 'Near White' 2 n  = 15, B.  'Carousel' 2 n  = 16, B. deanei 2 n  = 22, B. chartacea 2 n  = 32, B. keysii 2 n  = 32, B. pilosa 2 n  = 44, B. anethifolia 2 n  = 36 and B. citriodora 2 n  = 108. Studies in 20 genotypes of 18 species and one interspecific hybrid revealed that they are highly complex in terms of chromosome number, ploidy level, chromosomal length, karyotype constitution and asymmetry. Karyotype analysis indicated that Boronia taxa with high chromosome numbers are primitive and those with lower numbers are derived. The basic chromosome number for this genus is suggested to be x = 18. Analysis of chromosome number, variations of total chromosome length (TCL) and average chromosome length (ACL), Nombre Fondamental (NF) and karyotype asymmetry suggest that dysploid reduction is the major mechanism in Boronia karyotype evolution. Chromosomal rearrangements might also have been involved. Origin, chromosome number changes and spread of Boronia are discussed in relation to the species divergence and the geological and climatic changes of the Australian continent.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 142 , 309–320.     

Cytological evidence of natural hybridization in Brachiaria brizantha Stapf (Gramineae)

Two accessions of Brachiaria brizantha under cytological analysis showed 2 n  = 5x = 45 chromosomes. Pentaploidy probably resulted from natural hybridization between two species that were not closely related: an apomictic tetraploid male (2 n  = 4x = 36), and a sexual diploid female (2 n  = 2x = 18). The lack of affinity between genomes was clearly indicated by asynchrony during meiosis. The haploid genome ( n  = 9) showed unique behaviour, remaining univalent during prophase I and metaphase I, and undergoing sister-chromatid segregation and lagging at anaphase I. The laggard genome did not always reach the poles in time to be included in the telophase nucleus. However, when the inclusion was effective, this genome was distributed peripherally, changing the otherwise spherical nucleus shape. In the second division, the haploid genome behaved similarly, but as there was sister-chromatid segregation during the first division, the chromatids were slow to reach the poles, forming several micronuclei at telophase II. The two accessions were characterized as allo-autopentaploids, with the tetraploid genome (2 n  = 4x = 36) designated as B (from B. brizantha ) and the haploid genome as X, representing a species with a distinct genome having little affinity with the B genome. Thus, the hybrids' genome composition is represented by BBBBX. By comparing their meiotic behaviour with that observed in synthetic hybrids between B. brizantha and B. ruziziensis analysed previously, B. ruziziensis is the putative diploid sexual parent species in these pentaploid accessions.  © 2006 The Linnean Society of London , Botanical Journal of the Linnean Society , 2006, 150 , 441–446.     

Uniformity of karyotypes in Ligularia (Asteraceae: Senecioneae), a highly diversified genus of the eastern Qinghai–Tibet Plateau highlands and adjacent areas

Ligularia , a highly diversified genus in the eastern Qinghai–Tibet Plateau and adjacent areas, was chosen as a suitable subject in which to study speciation patterns in this 'hot spot' area at the chromosomal level. Chromosome numbers and karyotypes were studied in 23 populations of 14 species, most of which are endemic to this area. The basic number x  = 29 was confirmed for all species. Ligularia virgaurea was found to have diploid and triploid cytotypes, 2 n  = 58 and 87. Other species are only diploid, with 2 n  = 58. The karyotypes of all populations within any species, and all species spanning most sections and covering most of the morphological range in Ligularia , are very similar to each other, belonging to type 2A according to Stebbin's classification. This karyotype was also found in its close allies, e.g. Cremanthodium , Ligulariopsis , Parasenecio , and Sinacalia . Aneuploid reduction of chromosome number from 2 n  = 60 to 58 and karyotypic variation was found in Ligularia and its allies. Such a chromosomal pattern with few polyploids infers that variation of karyotype structure at the diploid level seems to be the predominant feature of chromosomal evolution in this group and sympatric speciation via hybridization and polyploidization has played a minor role in its species diversity.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 144 , 329–342.     

Taxonomic status and relationships of bracken ferns (Pteridium: Dennstaedtiaceae) of Laurasian affinity in Central and North America

Detailed quantitative comparisons confirm and extend the discrimination of four major morphotypes amongst brackens of Laurasian affinity in Central and North America. These are recognized here at subspecies level as: Pteridium aquilinum sspp. feei , pubescens , latiusculum , and pseudocaudatum . Measurements of spore size indicate that sporophytes of P. aquilinum ssp. feei are diploid (2 n  = 104), as are sspp. pubescens , latiusculum , and pseudocaudatum . Phenetic cluster analysis based on DNA fingerprinting by arbitrarily primed polymerase chain reaction groups these four subspecies as genomically more similar to each other than to any taxa from other geographical regions. The chloroplast haplotype of ssp. feei is the same as that of sspp. latiusculum , pseudocaudatum , and pubescens with respect to the absence of both of the short direct repeats in the rps 4– trn S region (haplotype A), whereas the European ssp. aquilinum (haplotype B) has one of these repeats, and the Southern Hemisphere brackens P. arachnoideum and P. esculentum (haplotype C) have the other.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 1–17.     

Genetic diversity in the endangered dysploid larkspur Delphinium bolosii and its close diploid relatives in the series Fissa of the Western Mediterranean area

Allozyme diversity was evaluated in four closely-related taxa of the Delphinium series Fissa distributed throughout the Western Mediterranean area. All are considered threatened plants. Delphinium bolosii and Delphinium mansanetianum are narrowly endemic to the Eastern Iberian Peninsula, whereas Delphinium fissum ssp. sordidum is found in a few populations across the Peninsula. Delphinium fissum ssp. fissum is more widely distributed but often in small and isolated populations. In this group, Delphinium bolosii is dysploid (2 n  = 18) whereas the other taxa are diploid (2 n  = 16). A total of 12 populations were surveyed, including all known locations for D. bolosii , D. mansanetianum , and D. fissum ssp. sordidum . Eleven enzyme systems were assayed and 15 loci were resolved. Markedly depauperate values for genetic diversity were obtained for D. mansanetianum ( H _e = 0.013) and D. fissum ssp. sordidum ( H _e = 0.044). The estimates for D. fissum ssp. fissum ( H _e = 0.071) were below the values expected for widespread species. Small population size and marginal distribution have probably contributed to the low variability observed in this group. By contrast, D. bolosii exhibited comparatively larger populations and greater genetic diversity ( H _e = 0.138). We suggest that, apart from population size and local adaptation, genetic diversity during speciation may have been promoted by dysploidy through genomic recombination.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 773–784.     

Iris stenophylla Hausskn. & Siehe ex Baker from Turkey and its cytology

A morphological study, both in the field and from herbarium material, showed that there are no convincing characteristics separating the Turkish endemics Iris stenophylla ssp. stenophylla and ssp. allisonii . A cytological survey revealed chromosome numbers of 2 n  = 24, 26 and 26 + 1B. No variation in either chromosome number or karyotype was found in ssp. allisonii , which always had 2 n  = 26, although the chromosome number and karyotypes of ssp. stenophylla were variable. Since neither morphological nor cytological differences were sufficient to separate the two subspecies, I. stenophylla ssp. allisonii is therefore reduced to a synonym of I. stenophylla .  © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 140 , 115−127.     

Karyomorphology of the endangered Trigonobalanus doichangensis (A. Camus) Forman (Fagaceae) and its taxonomic and biogeographical implications

Cytological studies were carried out for the first time on five populations of Trigonobalanus doichangensis in China and Thailand. In all populations, the pattern of interphase nuclei was of the simple chromocentre type, the mitotic prophases were of the proximal interstitial type and chromosome numbers were 2 n  = 2 x  = 14. Two B chromosomes were commonly observed at prophase and prophase–metaphase, but rarely at metaphase. Karyotype variation among the populations at the diploid level was limited, but there were some distinguishing cytological characters. Based on the comparison of all the available data on cytology, taxonomy, phytogeography and molecular systematics related to the genus Trigonobalanus , we recommend that the three species of Trigonobalanus comprise the subfamily Trigonobalanoideae and that the genus should not be segregated into three monotypic genera.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 154 , 321–330.