CHROMOSOME NUMBERS IN CUPHEA (LYTHRACEAE): NEW COUNTS AND A SUMMARY

The American genus Cuphea with ca. 260 species is extremely diverse with respect to chromosome number. Counts are now available for 78 species and/or varieties, or 29% of the genus. Included in this study are first reports for 15 taxa from Brazil, Cuba, Dominican Republic, Mexico, and Venezuela. Twenty-two different numbers are known for the genus, ranging from n = 6 to n = 54. The most common number in the primary center of species diversity in Brazil is n = 8, which is regarded as the base number of the genus. Two numbers are most common in the secondary center in Mexico, n = 10 and n = 12. Species with n = 14 or higher are considered to be of polyploid origin. Polyploids comprise 46% of the total species counted and appear in 9 of the 11 sections for which chromosome numbers have been reported. Aneuploid species comprise ca. 25% of the genus and are known from 7 of the 11 sections. The two subgenera are not characterized by different chromosome numbers or sequences of numbers. None of the 14 sections are circumscribed by a single chromosome number. Morphological and ecological variability in widespread, weedy species is correlated with differing chromosome numbers in some species whereas in others the chromosome number is stable. Summary of chromosome numbers by taxonomic section is presented. Section Euandra, centered in eastern Brazil, and the largest section of the genus, appears to be chromosomally most diverse. In section Trispermum, characterized by difficult, variable species with intermediate forms, two of the four species studied have polyploid races. Section Heterodon, endemic to Mexico and Central America and comprising most of the annual species of the genus, is best known chromosomally. Chromosome numbers have been counted for 25 of 28 species, and 12 different numbers are reported. The most advanced sections, Melvilla and Diploptychia, with numerous species occurring at higher altitudes, are characterized by high polyploids. Apomictic species occur in sect. Diploptycia. The cytoevolution of Cuphea is complex with frequent polyploid and aneuploid events apparently playing a significant role in speciation in both centers of diversity.     

Chromosome number variation and polyploidy in the genus Echinocereus (Cactaceae)

Analyses of meiotic and mitotic chromosomes were undertaken in 16 taxa of Echinocereus belonging to 12 species and all seven taxonomic sections (sensu Taylor). Chromosome numbers are reported for the first time for eight taxa, and previously published chromosome counts are confirmed for the remaining eight. Both diploid and polyploid counts were obtained. Eleven (69%) of the taxa surveyed were diploid (2n = 22); the five varieties of E. engelmannii were polyploid (2n = 44). Overall, chromosome counts are available for 23 of the 48 proposed species (sensu Taylor). Of these, 19 (82%) are diploid, and four (18%) are polyploid. Polyploid cytotypes are most common in the primitive sections, e.g., sections Erecti and Triglochidiatus, which suggests that polyploidy is probably a derived condition in Echinocereus. Polyploid taxa range from medium to high latitudes and elevations relative to the overall distribution of the genus. Polyploidy, hybridization, and cryptic chromosomal rearrangements are thought to be the major causes of the speciation events of the genus.     

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.     

CHROMOSOME NUMBERS IN UMBELLIFERAE. III

Chromosome numbers are reported for 156 collections representing 100 taxa of Umbelliferae. Approximately two thirds of the collections are from Mexico, Central and South America and indicate a high percentage of polyploid species in certain genera found in this area. Chromosome numbers for plants belonging to 78 taxa are published here for the first time, previously published chromosome numbers are verified for 18 taxa and chromosome numbers differing from those previously published are reported in seven instances. No chromosome counts have been previously published for nine of the genera included here. Further aneuploidy and polyploidy were found in Eryngium, and Lomatium columbianum has been found to be a high polyploid with 2n = 14x. Every chromosome count is referable to a cited herbarium specimen.     

New chromosome counts and evidence of polyploidy in Haageocereus and related genera in tribe Trichocereeae and other tribes of Cactaceae

Chromosome numbers for a total of 54 individuals representing 13 genera and 40 species of Cactaceae, mostly in tribe Trichocereeae, are reported. Five additional taxa examined belong to subfamily Opuntioideae and other tribes of Cactoideae (Browningieae, Pachycereeae, Notocacteae, and Cereeae). Among Trichocereeae, counts for 35 taxa in eight genera are reported, with half of these (17 species) for the genus Haageocereus. These are the first chromosome numbers reported for 36 of the 40 taxa examined, as well as the first counts for the genus Haageocereus. Both diploid and polyploid counts were obtained. Twenty nine species were diploid with 2n=2x=22. Polyploid counts were obtained from the genera Espostoa, Cleistocactus, Haageocereus, and Weberbauerocereus; we detected one triploid (2n=3x=33), nine tetraploids (2n=4x=44), one hexaploid (2n=6x=66), and three octoploids (2n=8x=88). In two cases, different counts were recorded for different individuals of the same species (Espostoa lanata, with 2n=22, 44, and 66; and Weberbauerocereus rauhii, with 2n=44 and 88). These are the first reported polyploid counts for Haageocereus, Cleistocactus, and Espostoa. Our counts support the hypothesis that polyploidy and hybridization have played prominent roles in the evolution of Haageocereus, Weberbauerocereus, and other Trichocereeae.     

CHROMOSOME NUMBERS IN CENCHRUS (GRAMINEAE)

Gametic chromosome numbers are reported for 22 populations representing 6 taxa in the genus Cenchrus. Numbers of n = 17 were obtained for C. incertus M. A. Curtis, C. longispinus (Hack.) Fern., and for the previously unreported C. mitis Anderss. Populations of C. echinatus L. have the number n = 34, and C. myosuroides H.B.K. n = 35. Irregular meiosis was observed in 2 chromosomal races of C. ciliaris L. having numbers of n = 18 and n = ca. 16, respectively.     

SYSTEMATIC SIGNIFICANCE OF CHROMOSOME NUMBERS IN ACMELLA (ASTERACEAE)

Chromosome counts are reported for 372 individuals from 202 populations in 26 taxa of Acmella (Asteraceae: Heliantheae). Chromosome numbers for 15 taxa are first reports. A review of previous counts and the new reports supports a basic chromosome number of 13 for the genus. The results show that polyploidy, sometimes accompanied by hybridization and asexual reproduction, is widespread in Acmella and has contributed to the taxonomic difficulties in the genus. These factors have produced a variable polyploid pillar complex in sect. Acmella. In one taxon in this complex, A. oppositifolia var. oppositifolia, intrataxon and even intrapopulational chromosomal variation has been detected. Morphological studies in conjunction with observations of meiotic pairing suggest that most polyploids are alloploid in origin. The occurrence of polyploidy in 16 of the 27 taxa known chromosomally emphasizes the important role this process has had in speciation within Acmella. Although intrataxon chromosomal variation has limited the taxonomic utility of chromosome numbers, a few examples are presented in which these data have been valuable for separating some pairs of closely related taxa (A. decumbens var. affinis from var. decumbens and A. poliolepidica from A. oppositifolia).     

CHROMOSOME NUMBERS IN BROMELIACEAE

Eighty-three chromosome counts are reported for 72 taxa of the Bromeliaceae. Fifty-eight of these counts are the first known chromosome number reports for their respective taxa. A model of chromosomal evolution in the Bromeliaceae (n = 25) is presented. The model is parsimonious and consistent with existing data on meiotic chromosome numbers within the family and in the closely related Velloziaceae (n = 9). Two hypothesized paleodiploids (n = 8 and n = 9) hybridized to form a tetraploid that in turn hybridized with the n = 8 lineage. The resultant n = 25 is the extant base number for the family. Two alternative hypotheses could explain the unique extant base number (n = 17) for Cryptanthus: 1) Cryptanthus represents the paleotetraploid level, i.e., prior to the second round of hybridization, or 2) the lower number represents the result of a more recent series of aneuploid reductions from n = 25. Given the existence of intergeneric hybrids involving Cryptanthus, aneuploid reduction is the more likely interpretation.     

ISOZYME NUMBER IN SUBTRIBE ONCIDIINAE (ORCHIDACEAE): AN EVALUATION OF POLYPLOIDY

The Oncidiinae has attracted attention because of the variation it exhibits in chromosome number, n = 5–30, which is greater than the range in the rest of the Orchidaceae. The genus Psygmorchis, with n = 5 and 7, has been a particular focus of controversy, and many authors have suggested that 5 and 7 are the base numbers for the subtribe. The other taxa in the subtribe presumably evolved through hybridization and polyploidy. Other workers have found that the lowest counts correlate with derived morphological conditions and have hypothesized that these low numbers result from aneuploid reductions, while higher numbers are associated with ancestral morphologies and are not the result of polyploidy. These two hypotheses were evaluated by determining isozyme numbers for 13 enzymes in species that span the chromosomal range known for the Oncidiinae (n = 5–30). Isozyme number has been shown to be a reliable indicator of polyploidy in angiosperms because polyploids display isozyme multiplicity relative to diploids. This analysis revealed no differences among species in isozyme number for the enzymes examined. Therefore, our data reject the hypothesis that species with higher chromosome numbers are polyploid.     

CYTOGEOGRAPHIC EVIDENCE FOR THE EVOLUTION OF DISTYLY FROM TRISTYLY IN THE NORTH AMERICAN SPECIES OF OXALIS SECTION IONOXALIS

A survey of haploid chromosome numbers of 18 North American taxa of Oxalis section Ionoxalis was initiated to determine the relationship between ploidal level, geographic distribution, and the occurrence of tristyly and distyly. Although chromosome numbers in the section are variable, the majority of tristylous populations are diploid. Among the distylous taxa a greater diversity of ploidal levels exists, with the higher chromosome numbers predominating. In section Ionoxalis the majority of the tristylous taxa are geographically restricted endemics of southern Mexico, while the distylous taxa have more extensive distributions ranging to the north. The association of diploidy and geographic endemism in the majority of the tristylous taxa suggests that these species are relictual. A few widespread tristylous taxa are polyploid, and often somewhat weedy. The probable derivation of widespread polyploid species from the restricted diploid endemics of southern Mexico appears to have been accompanied by the evolution of distyly from tristyly. The frequent association of polyploidy and distyly in section Ionoxalis has apparently resulted from the concurrence of two evolutionary trends: increase in ploidal level and the derivation of distyly from tristyly.     

CHROMOSOME NUMBERS IN THE GENUS ANTHURIUM (ARACEAE) II

Chromosome numbers were determined for 86 Anthurium species. Fifty-one of these were newly determined with counts ranging from 2n = 24 to 66 and 30 being the most common. All known Anthurium chromosome numbers were summarized, and 43 taxonomic changes were made in the previous reports to reflect current taxonomy. In terms of somatic chromosome numbers, the numbers form four polyploid series of 20–40–60, 24–30–48–84, 28–56 and 30–60–90–ca. 124. Paleoaneuploidy, polyploidy and B-chromosomes are basic features of the genus, but subsequent recent aneuploidy is not. The exact nature of chromosome evolution in Anthurium remains to be elucidated.     

CHROMOSOME COUNTS OF COMPOSITAE FROM THE UNITED STATES AND MEXICO

Chromosome counts are reported for 126 taxa representing 122 species and 61 genera of Compositae. First reports include two genera, Stylocline (n = 14) and Chromolepis (n = 19), 17 species, two infraspecific taxa, and one interspecific hybrid. Five additional taxa have chromosome numbers differing from previously published accounts. Carminatia is reinstated to generic status.     

CHROMOSOME NUMBERS OF THE EAST AFRICAN GIANT SENECIOS AND GIANT LOBELIAS AND THEIR EVOLUTIONARY SIGNIFICANCE

The gametophytic chromosome number for the giant senecios (Asteraceae, Senecioneae, Dendrosenecio) is n = 50, and for the giant lobelias (Lobeliaceae, Lobelia subgenus Tupa section Rhynchopetalum) it is n = 14. Previous sporophytic counts are generally verified, but earlier reports for the giant senecios of 2n = 20 and ca. 80, the bases for claims of intraspecific polyploidy, are unsubstantiated. The 14 new counts for the giant senecios and the ten new counts for the giant lobelias are the first gametophytic records for these plants and include the first reports for six and four taxa, respectively, for the two groups. Only five of the 11 species of giant senecio and three of the 21 species of giant lobelia from eastern Africa remain uncounted. Although both groups are polyploid, the former presumably decaploid and the latter more certainly tetraploid, their adaptive radiations involved no further change in chromosome number. The cytological uniformity within each group, while providing circumstantial evidence of monophyly and simplifying interpretations of cladistic analyses, provides neither positive nor negative support for a possible role of polyploidy in evolving the giant-rosette growth-form.     

Chromosome numbers in the genus Mimosa L.: cytotaxonomic and evolutionary implications

Chromosome numbers were determined for 125 accessions of 92 taxa of Mimosa from all five of Barneby??s (Mem New York Bot Gard 65:1?C835, 1991) taxonomic sections. For 69 species, 1 subspecies and 8 varieties, chromosome numbers are presented for the first time, for 6 species and 1 variety previously published data have been confirmed and for 3 species and 2 varieties different numbers were found. Results show that 74% of the accessions were diploid (2n?=?2x?=?26) and 26% polyploid, these mostly tetraploid (2n?=?4x?=?52) but with two triploid (2n?=?3x?=?39). These results double the number of Mimosa species for which the chromosome count is known from less than 10% previously reported to more than 20%, representing an important advance in the cytotaxonomy of this legume genus. These results together with literature data show that ca. 78% of Mimosa species are diploid. Polyploids are present in most of the taxonomic sections and in different lineages across the genus. No particular chromosome number is restricted to a given section or lineage. A possible relation between geography, species distribution, polyploidy and invasiveness was detected, however, further studies based on more accessions, especially from higher latitudes, are required before firm conclusions can be drawn.     

CHROMOSOME NUMBERS IN PERITYLE AND RELATED GENERA (PERITYLANAE-COMPOSITAE)

Chromosome numbers are presented for 28 species of the genus Perityle, one putative inter-sectional hybrid, two species of Amauria, one species of Eutetras, and one species of Pericome. For Perityle, initial counts are recorded for 12 species of sect. Laphamia (n = 16, 17, 18, 36, ca. 102) and 11 species of sect. Perityle (n = 11, 12, 13, 16, 17, 18, 19, 34, 51). Chromosome numbers for the two species of Amauria (n = 18) are first reports for the genus. Including the current information, chromosome numbers have been recorded for 37 of the approximately 50 species recognized for Perityle. At least 24 taxa have numbers of n = 17, suggesting a base chromosome number of x = 17 for Perityle.     

Chromosome number of <Emphasis Type="Italic">Orthophytum</Emphasis> species (Bromeliaceae)

The genus Orthophytum Beer comprises 53 species, all narrow endemics to south-eastern and north-eastern Brazil. In this study we present meiotic and mitotic chromosome numbers of 12 species of this important genus in Bromeliaceae. For six of these taxa we are reporting the first cytogenetic study. Orthophytum albopictum, O. amoenum and O. burle-marxii presented 2n = 100 chromosomes and O. hatschbachii, O. mucugense, O. vagans, O. supthutii, O. zanonii and O. ophiuroides showed 2n = 50 chromosomes. These results are consistent with the proposed basic number of x = 25 for Bromeliaceae family. In the genus Orthophytum, polyploidy seems to play an important role in chromosome evolution associated with habitat differentiation among diploid and polyploid species.     

CHROMOSOME NUMBERS IN COMPOSITAE. VI. SENECIONEAE. II

Chromosome counts are reported for 76 taxa and 2 natural hybrids of tribe Senecioneae (Compositae). First counts are reported for several species of Senecioneae as well as for the genera Cadiscus and Whitneya. New chromosome numbers are added to those previously known in Arnica, Cacalia, and Senecio. Additional counts from Arnica support our previous suggestion that x = 19 for this genus. It is assumed that observed meiotic irregularities are associated with apomixis in this genus. Basic chromosome numbers for various New World sections of Senecio are proposed, and certain problems of sectional relationships in this genus are discussed. Chromosome numbers and plant morphology of Cadiscus, Hulsea, and Whitneya indicate that these genera should be removed from Helenieae to Senecioneae. The possible affinity of the anomalous genus Adenocaulon with Mutisieae is discussed. Data presented in the paper further support our earlier proposal that the basic chromosome number for Senecioneae is x = 10.     

Polyploidy and new chromosome counts in Helichrysum (Asteraceae,Gnaphalieae)

Mitotic chromosome numbers are reported for 31 populations representing 28 taxa of Helichrysum. Twelve are new and eight others provide confirmation of a unique previous reference. A new chromosome number, 2n = 42, is reported for H. odoratissimum. Polyploidy is confirmed as the most significant evolutionary trend in chromosome number within the genus. Chromosome data agree with trends observed in phylogenetic studies: a South African and diploid origin of the genus, followed by a radiation and diversification in southern Africa and several migrations towards the north of the African continent, the Mediterranean basin and Asia. Expansion and diversification of the genus have been accompanied by several genome duplications which have led to the acquisition of the tetraploid, hexaploid and octoploid levels, all in several independent events. Both autopolyploidy and allopolyploidy are suggested as probable speciation agents within the genus. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158 , 511–521.     

CYTOTAXONOMY OF CESPITOSE ZINNIAS

Torres , Andrew M. (U. Wisconsin, Milwaukee.) Cytotaxonomy of cespitose zinnias. Amer. Jour. Bot. 49(10): 1033–1037. Illus. 1962.—The results of hybridization studies among 5 of the 6 cespitose species of Zinnia are reported. Analyses of meiosis in the F₁ hybrids suggest there are 2 genomes, A and B, in the polyploid taxa. The A genome apparently exists in the diploid state in 2 species, but the B genome is known only from polyploid taxa. The chromosome number of Z. oligantha (2n = 20) is reported for the first time.     

CHROMOSOME NUMBERS IN THE LEGUMINOSAE. III. SPECIES OF THE SOUTHWESTERN UNITED STATES AND MEXICO

Turner, B. L., and Olin S. Fearing. (U. Texas, Austin.) Chromosome numbers in the Leguminosae. III. Species of the Southwestern United States and Mexico. Amer. Jour. Bot. 47(7) : 603–608. Illus. 1960.—Chromosome counts for 43 species of the Leguminosae from the southwestern United States and Mexico have been reported. These include first reports for 42 taxa of which 16 are for the subfamily Mimosoideae. Olneya tesota (2n = 18) is the only new generic count listed. Chromosome reports of particular significance include a single polyploid count for a North American species of Acacia, as well as diploid and tetraploid counts for closely related taxa in this genus. Four species of the genus Schrankia were found to be diploid with In = 26, indicating a base of x = 13 instead of the x = 8 reported by some previous workers. Leucaena pulverulenta was found to have a diploid count of 2n = 56 indicating a base of x = 14.