ANEUSOMATY IN ANEUPLOID POPULATIONS OF CLAYTONIA VIRGINICA

Lewis Walter H. (Stephen F. Austin State Coll., Nacogdoches, Texas.) Aneusomaty in aneuploid populations of Claytonia virginica. Amer. Jour. Bot. 49(9): 918–928. Illus. 1962.—From 2 central east Texas populations of Claytonia virginica, 15 chromosome numbers, 2n = 14, 15, 16, 18, 25, 26, 27, 28, 29 30, 31, 32, 33, 36, and 58, were found among a sample of 181 plants. The most frequently encountered numbers were 2n = 14, 28, and 29. Among an additional 14 plants the pollen mother cells in the same bud differed from one another in chromosome number, as well as the pollen and premeiotic cells from the same plant. The chromosomes of the most unstable plant varied from 2n = 14–36. Numerous meiotic abnormalities, including inversions, dicentrics, bridges, fragments, non-disjunctions, univalents, and multivalents, were observed for the aneusomatic and trisomic plants. It is suggested that the origin of the aneusomatics is related to the numerical disparity of the gametic chromosomes composing them. Since the species is perennial in habit, thereby allowing the unstable plants to produce gametes with varying chromosome numbers year after year, it is further proposed that the wide range of aneuploid known for C. virginica resulted, at least in part from the presence of aneusomatic individuals.     

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

Chromosome numbers were determined for 63 Anthurium species. Thirty-eight of these were newly determined. Generally the present work confirmed existing chromosome counts when these were available for comparison. The most common somatic chromosome number found was 30, but counts ranged from 2n = 20 to 90. In a few instances conflicting counts were obtained. B chromosomes were found frequently in Sect. Cardiolonchium and varied in number from one to three. Four polyploid series were evident from all available counts: 20-40, 24-30-48-84, 28-56 and 30-60-90-ca 124. Most species were part of the polyploid complex based on 30. Although species were not observed with n = 5, 6 or 7, movement among the basic numbers was considered to have occurred at this level. The relationship among these basic numbers and n = 15 (x₂) is still obscure.     

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 MORPHOLOGY IN THE GENUS SAMBUCUS

Two basic chromosome karyotypes were found in the genus Sambucus. Chromosome numbers were observed to be 2n = 38 for S. callicarpa, S. cerulea, S. glauca, S. kamtschatica, S. melanocarpa, S. mexicana, S. miquelli, S. sibirica, and S. sieboldiana and 2n = 36 for S. simpsonii and S. williamsii. Measurements of 18 karyotypes are presented. The major differences between the two basic chromosome karyotypes can be explained as the result of a mis-division of a metacentric chromosome giving rise to two telocentric chromosomes, thus reducing the number of metacentrics from five to four and increasing the chromosome number from 2n = 36 to 2n = 38. Observed chromosome aberrations and aneuploidy may result from unstable telocentric chromosomes.     

MODELS OF RETICULATE EVOLUTION IN THE CORAL GENUS ACROPORA BASED ON CHROMOSOME NUMBERS: PARALLELS WITH PLANTS

Somatic chromosome number was determined for 22 species of the scleractinian coral genus Acropora, three species of Montipora, and one species of Fungia, using colchicine-treated cells of externally developing embryos. Most had 28 chromosomes, except for six species of Acropora, which had somatic numbers of 24, 30, 30, 42, 48, and 54. Two models that invoke a combination of polyploidy and aneuploidy are presented to account for the observed intrageneric variation in somatic chromosome number. The ability to propagate clones through vegetative fragmentation plus the opportunities for hybridization during multispecies spawning events may have contributed to the development of polyploidy and rapid, sympatric speciation in the uniquely speciose coral genus Acropora.     

Genomic dispersion of 28S rDNA during karyotypic evolution in the ant genusMyrmecia (Formicidae)

The chromosomal localization of 28S rDNA was investigated in 16 speices of the Australian ant genus Myrmecia, with 2n numbers ranging from 4 to 76, using the fluorescence in situ hybridization method and karyographic analysis. A unique phenomenon was observed: the number of chromosomes carrying 28S rDNA increases from 2 in species with low chromosome numbers to 19 in species with high chromosome numbers. This is termed rDNA dispersion. Centric fission and a reciprocal translocation that occurs in C-bands were detected as the major mechanisms involved in rDNA dispersion. Received: 22 March 1996; in revised form: 3 June 1996 / Accepted: 4 June 1996     

CHROMOSOMES AND SYSTEMATICS OF ASPLENIUM SECT. HYMENASPLENIUM (ASPLENIACEAE)

Gametic and somatic chromosome numbers of eight Asian species belonging to Asplenium sect. Hymenasplenium were determined. Seven species were observed to have chromosome numbers based on x = 39, and one on x = 38. These chromosome numbers are exceptional in Asplenium which is well known to have chromosomes of n = 36 or multiples thereof. Decisions on the taxonomic status of the species of section Hymenasplenium were facilitated by cytological observations. Systematic recognition of this section is also supported by the peculiarity in the chromosome numbers, and evidence for the addition to the section of several other species is presented.     

CYTOTAXONOMIC STUDIES IN THE EUPHORBIACEAE,SUBTRIBE PHYLLANTHINAE

Webster , Grady L. (Purdue U., Lafayette, Ind.), and J. R. Ellis . Cytotaxonomic studies in the Euphorbiaceae, subtribe Phyllanthinae. Amer. Jour. Bot. 49:(1): 14–18. Illus. 1962.—Chromosome numbers are reported for 18 species of mostly West Indian Euphorbiaceae, subtribe Phyllanthinae, 13 of these for the first time (including the first published count for the genus Margaritaria). For 4 species, a number different from previous determinations has been recorded. The base chromosome number in Breynia, Fluggea, Margaritaria, and most species of Phyllanthus appears to be 13. However, in Phyllanthus subg. Isocladus haploid numbers of 8 and 18 were observed. One species, Phyllanthus pulcher, is a sterile hexaploid (n = 39) of presumably hybrid origin. The cytological data do not support Perry's suggestion that annual taxa are primitive in the Euphorbiaceae.     

BIOSYSTEMATIC INVESTIGATIONS IN THE GENUS AGROPYRON. I. CYTOLOGICAL STUDIES OF SPECIES KARYOTYPES

Schulz -Schaeffer , Jurgen (Montana State Coll., Bozeman), and Peter Jurasits . Biosystematic investigations in the genus Agropyron. I. Cytological studies of species karyotypes. Amer. Jour. Bot. 49(9): 940–953. Illus. 1962.—Twenty-five species of the genus Agropyron are analyzed cytologically in this presentation. Accession numbers, names of collectors, locations where seed was collected, and observed chromosome numbers are listed. Chromosome numbers of A. panormitanum (2n = 28), A. lolioides (2n = 58), A. brachyphyllum (2n = 42), A. ciliatiflorum (2n = 28), A. kosanini (2n = 56), A. pseudorepens (2n = 28), A. squamosum (2n = 42), and A. subulatum (2n = 56) are reported. No previous counts in these species are known to the authors. Chromosome counts of A. caespitosum (2n = 42) and A. elongatiforme (2n = 58), deviate from previous reports. Idiograms of all species and photomicrographs of mitotic metaphase root tip cells of 14 species are presented. The distribution of 11 satellite-chromosome types in 25 Agropyron species is shown in Table 2. The proportions of these 11 satellite-chromosome types are recorded in Table 3. The significance of these satellite chromosomes as indicator chromosomes for genome relationships is discussed together with the pertinent literature.     

CHROMOSOME COUNTS IN CHEILANTHES AND ASPIDOTIS WITH A CONSPECTUS OF THE CYTOLOGY OF THE SINOPTERIDACEAE

Confirmatory, corrective and new chromosome counts are listed for species in the genus Cheilanthes, and a new chromosome count is given for a member of the genus Aspidotis. An analysis of five collections of C. castanea revealed no significant morphological differences despite the different chromosome numbers. The ploidy level of all known species in genera of the Sinopteridaceae is summarized, revealing directions in which future research might proceed to complete our cytological knowledge of this family.     

THE HORDEUM VIOLACEUM COMPLEX OF IRAN

Fifty-seven Iranian collections of Hordeum violaceum Boiss. & Huet, a perennial forage grass, contained diploid (2n = 14), tetraploid (2n = 28), and hexaploid (2n = 42) chromosome races. All collections came from moderate to high elevations in the Alborz and Zagros mountains and adjacent plateau areas of Iran. Each chromosome race had a discrete distribution, and the hexaploids were the most widespread. The diploids were cytologically regular, except for a chromosome interchange that occurred in about half of the plants. The tetraploids and hexaploids behaved cytologically as autopolyploids. The hexaploids were taller, coarser and later-flowering than the diploids and tetraploids, and they had fewer but thicker culms and larger seeds. The tetraploids were the leafiest and most productive, making them the most desirable from an agronomic standpoint. All races were more or less self-sterile, a characteristic that sets H. violaceum apart from most other Hordeum species. The taxonomic status of H. violaceum and its closest relatives, H. turkestanicum Nevski and H. brevisubulatum Link, is uncertain because of close morphological similarities and the occurrence of chromosome races in each taxon.     

THE CYTO-ECOLOGY OF FOUR SPECIES OF TRILLIUM FROM WESTERN NORTH CAROLINA

The major center of variability in the genus Trillium occurs in the southern Appalachian mountains of the eastern United States. The karyotypic variation existing within T. cuneatum Raf., T. grandiflorum (Michx.) Salisb., T. erectum L., and T. gleasoni Fern., the four most abundant Trillium species in western North Carolina, was analyzed and compared with the variation in gross morphology and the ecological associations of the respective species. The number of types of each kind of chromosome (A-E), as exhibited following “nucleic acid starvation” by cold treatment, varied widely from species to species. Chromosome types varied within each species and within populations in the numbers, sizes, and positions of euchromatic and heterochromatic segments. No 10-chromosome karyotype and only one 5-chromosome complement was found to be duplicated in any two plants which belonged to different species. Trillium cuneatum with eight chromosome types was morphologically stable and occurred in a limited geographic area. Trillium gleasoni, characteristically adapted to elevations near 2,000 feet, contained 32 chromosome types and exhibited a high morphological variability. Trillium erectum (25 types) and T. grandiflorum (23 types) were also intermediate in morphological variability. These two species had the widest geographical range. Karyotypes were analyzed from pure stands of each of the four species and for each species from mixed stands of two or more of the species growing in close association. These Trillium species are maintaining a high level of karyotypic and gross morphological variability within comparatively limited geographical areas. None of the observed karyotypes in any species is likely to have arisen by recent interspecific hybridization. The composite karyotype of each species could be used as an aid to classification in the genus Trillium.     

THE CYTOLOGY OF SOME SPECIES OF THE GENUS NOTHOLAENA

Eight taxa in the genus Notholaena were examined for their chromosome numbers; one of the eight had two cytotypes (2 N, 4 N). The other seven consisted of five triploids and two diploids. Observations were also included on spore number and prothallial glandularity whenever possible.     

SOME CHROMOSOME NUMBERS OF DRAPARNALDIA

The variability exhibited by Draparnaldia both in nature and in the laboratory makes it difficult to identify the species. The natural variability of Draparnaldia was amplified by the environmental conditions and the media used in this study. With the hope that chromosome studies would aid in taxonomic characterization by providing additional differentiating criteria, special attention was devoted to adapting techniques which could be used to determine chromosome numbers of Draparnaldia isolates. The chromosome numbers reported herein are as follows: (1) Draparnaldia glomerata, Isolate #1, isolated from Davis Falls, Montevallo, Alabama, was found to have a chromosome number of 13. (2) Draparnaldia Isolate #2, an unidentified species obtained from Anniston, Alabama, was found to have a chromosome number of 13. (3) Draparnaldia acuta, Isolate #3 from Northwood Lake, Northport, Alabama, exhibited 26 chromosomes. (4) Draparnaldia plumosa strain 423 (Indiana Culture Collection), 418/a (Cambridge) was observed to have a chromosome number of 13.     

GROWTH AND ORGANIZED DEVELOPMENT OF CULTURED CELLS IV. THE BEHAVIOR OF THE NUCLEUS

Mitra , J., Marion O. Mapes , and F. C. Steward . (Cornell U., Ithaca, New York.) Growth and organized development of cultured cells. IV. The behavior of the nucleus. Amer. Jour. Bot. 47(5) : 357—368. Illus. 1960.–The nuclei and the chromosomes of carrot cells have been examined at various stages throughout the following sequence: (1) growth of a tissue culture from a preformed explant of secondary phloem from the carrot root; (2) growth and multiplication of carrot cells freely suspended in a liquid medium; (3) growth and re-formation of organs (roots) and whole plants (including flowers) from cells in the freely suspended state. The cells of the carrot are normally diploid (2n = 18), the cells which develop in the explant are also diploid, and the cells of the re-formed organs, and even the flowers developed upon plants grown from cells, are also normal and diploid; normal meioses also occur. Nevertheless, the wide range in growth and form of the freely suspended cells is accompanied by a rich diversity of cytological conditions; these include tetraploid and highly polyploid nuclei which divide, haploidy and such chromosomal aberrations as di- and even tri-centric bridges. Two division figures showing chromosome numbers at different levels of ploidy were seen within the confines of one large cell, and, in another, 2 adjacent division figures were observed with chromosome numbers lower than diploid. Small thick-walled, densely protoplasmic cells divide to form bi- and tetra-nucleate conditions, and in a giant cell a highly multinucleate condition has been seen. Despite this, however, all the regenerated roots and plants yet examined are normally diploid. The implications of these events are discussed.     

ON THE METHODS OF EXPERIMENTAL TAXONOMY

By studying seedling progenies from individual plants it may be decided whether the material under investigation is allogamous, autogamous or apomictic. Chromosome counts disclose whether the material is cytologically stable or variable. If variation occurs it may be a question of polyploidy or aneuploidy. Aneuploidy may either be an occasional consequence of polyploidy or it may represent dysploidy and the formation of new basic numbers. Chromosome counts combined with measurements of chromosome size may reveal cases of pseudopolyploidy of the kind first observed in Luzula. If chromosome morphology is different between two taxa this indicates reproductive isolation. Different species usually differ with regard to their chromosome structure. Studies of meiosis are desirable in polyploids in order to distinguish between auto- and alloploidy. Cases of genic control of meiosis in polyploids of Phleum and Triticum demonstrate, however, that partial or complete homology between genomes does not always result in multivalent formation. Apparent alloploids may in reality be more or less autoploid. Incompatibility is not a reliable criterion of species differentiation. Strong or absolute barriers between diploids and autotetraploids may have purely quantitative causes. Hybrid sterility is not always a reliable measure of the degree of genetic difference between the parents, but may be caused by heterozygosity for chromosomal rearrangements. Cytological and experimental methods are, nevertheless, indispensable tools in plant taxonomy.     

CHROMOSOME NUMBERS OF CAMPANULACEAE. II. THE LOBELIA TUPA COMPLEX OF CHILE

Gametic chromosome numbers are reported for 27 collections representing the four species of the Lobelia tupa complex (Campanulaceae, Lobelioideae) in Chile; all are n = 21. This represents the first report of chromosome numbers for L. bridgesii Hook. & Arn., L. excelsa Bonpl., and L. polyphylla Hook. & Arn., and confirms previous reports of this number in L. tupa L. As the basic chromosome number of Lobelioideae is x = 7, these species are interpreted as hexaploids. Higher polyploids are extremely rare among Lobelioideae; most of those previously reported have been either sporadic individuals or populations within an otherwise diploid or tetraploid species, or occasional species within an otherwise diploid and tetraploid lineage. This is the first report of an entire complex of lobelioid species that is uniformly hexaploid. This suggests that the Chilean endemics are relatively derived within Lobelia, and offers some support for the monophyly of the complex.     

Karyotype evolution by centromeric fission inZamia (Cycadales)

The chromosome numbers of several species ofZamia from Mexico are reported.Z. paucijuga, distributed from central Oaxaca to Nayarit, has been found to have 2n = 23, 25, 26, 27 and 28. 2n = 28 is the highest chromosome number yet found in the cycads. Karyotypes of this species differ principally in the number of telocentric and metacentric chromosomes present in each; 2n = 23, 25, 26, 27 and 28 were found to have 5, 3, 2, 1 and 0 metacentric and 8, 12, 14, 16 and 18 telocentric chromosomes, respectively.Z. fischeri has been found to be 2n = 16,Z. furfuracea andZ. loddigesii 2n = 18.Zamia paucijuga on the basis of morphological and ecological characteristics, is considered to be an advanced member of this genus. Chromosome and karyotype evolution inZ. paucijuga may have occurred by centromeric fission of metacentric chromosomes; the karyotypes ofZ. paucijuga are strongly asymmetrical, suggesting that they evolved recently.     

THE PROBLEM OF PLOIDY IN ECHEVERIA (CRASSULACEAE) I. DIPLOIDY IN E. CILIATA

The largely Mexican genus Echeveria is characterized by an extensive series of dysploid chromosome numbers, with every gametic number from 12 to 34 known in at least one species. Within this nearly three-fold range of numbers, the boundary between diploidy and tetraploidy is not immediately apparent. However, species of Echeveria can be hybridized in an extraordinary number of combinations, both among themselves and with related genera, and study of the morphology of the hybrids and the pairing of their chromosomes provides information that helps to identify the ploidy of the parents. This paper reports observations from study of 80 hybrids between E. ciliata (n = 25) and 73 other species and/or cytotypes. Hybrids between E. ciliata and definite diploids are all nicely intermediate morphologically, whatever the chromosome numbers. In these same hybrids, most chromosomes become involved in pairing at meiosis, and the number of paired elements (bivalents and multivalents) approaches or equals, but never exceeds, the number of chromosomes received from the lower-numbered parent. In most cells, relatively few univalents are present, sometimes none. These observations are considered to indicate that all paired elements include at least one chromosome from each parent and therefore that pairing occurs between chromosomes of different parents only (allosyndesis). Since none of the 25 gametic chromosomes of E. ciliata is able to pair with any other, although they do pair very extensively with chromosomes from many other species having a wide range of numbers, E. ciliata is considered to be diploid in spite of its relatively high chromosome number. On the other hand, hybrids of E. ciliata with definite polyploids resemble the latter much more closely in their morphology, and at meiosis most or all pairing occurs by autosyndesis between chromosomes received from the polyploid parent, while the chromosomes from E. ciliata generally remain unpaired. In these respects most, but not all, species of Echeveria having as many as 34 gametic chromosomes have the same properties as E. ciliata and also are considered to be diploid. The ancestral chromosome number in the genus is not clear, but it is probably near the upper end of the series of dysploid numbers.