APOMIXIS IN EUPATORIUM TANACETIFOLIUM (COMPOSITAE)

Cytogenetics and embryological studies of male sterility have been reported for the first time in Eupatorium tanacetifolium Gill, ex H. et A. (Gyptis pinnatifida Cass.). This species produces viable seeds but abnormal pollen that is not shed by the anthers. There are great abnormalities in karyokinesis and cytokinesis in microsporogenesis that result in irregular sporads formed by 5–10 cells of variable size, shape, and chromosome number. There is an irregular distribution of chromosomes, due to absence of regular pairing and disjunction, presence of chromatinic bridges in most of telophases, and to succesive aberrant cytokinesis without formation of cell plate and with variably oriented walls. The two chromatids of each chromosome presumably remain joined until the end of the process. Somatic chromosome number of 2n = 30 is reported for one population of this species, an apomict taxon of probable triploid origin. Embryo-sac ontogeny is of the Antennaria type of diplospory, wherein embryo and endosperm development are parthenogenetic.     

SEED FERTILITY IN TRAGOPOGON HYBRIDS (COMPOSITAE)

The seed fertility of 172 interspecific and 32 intraspecific F₁ hybrids in the genus Tragopogon was determined. Intrageneric barriers to interbreeding were variable; some were weak and others quite strong. Maternal influences on fertility were found in 18 pairs of reciprocal interspecific crosses. It was postulated that cytoplasmic and nuclear factors interacted to determine the level of seed fertility. Although F₁'s were generally sterile or semi-sterile, the proportion of fertile seeds produced in most crosses increased in the F₂ generation. In two cases, however, a significant decrease was observed.     

LEAF DEVELOPMENT IN SENECIO ROWLEYANUS (COMPOSITAE)

Prolonged apical growth of the leaf primordium and the presence of distinct marginal meristems do not occur in Senecio rowleyanus. Intercalary cell divisions accompanied by radial expansion of derivatives from an adaxial meristem account for the spherical shape of the leaf. The “window” in the lamina marks the position of the adaxial meristem and precludes interpretation of the leaf as being unifacial. Stomata are mesoperigenous and anomocytic in type. Schizogenous secretory canals occur in both the leaf and the stem, and their association with vascular bundles is discussed. The anatomy of the leaf is interpreted in terms of xeromorphy.     

CYTOTAXONOMIC STUDIES IN CHRYSOTHAMNUS (ASTEREAE,COMPOSITAE)

The basic chromosome number for Chrysothamnus is x = 9 as determined by 234 original counts representing all species. Polyploidy is frequent only in C. viscidiflorus where diploids, tetraploids, and hexaploids are found. Pollen size in the genus is basically correlated with style length rather than ploidy level. Most aspects of meiosis appear normal except for the tendency for nucleolar fragmentation. To reduce chromosome clumping during meiosis, an ice-water pretreatment was utilized. Karyotypes in Chrysothamnus reflect similar trends of specialization noted in chromosome structure for other Compositae. The taxa are predominantly self-fertilized; however, one instance of interspecific hybridization is noted. Taxonomic significance of the chromosome numbers, karyotypes, and breeding system in Chrysothamnus is discussed.     

CHROMOSOME NUMBERS AND PHYLOGENY IN MELAMPODIUM (COMPOSITAE)

The haplord chromosome numbers of n = 9, 10, 11, 12, 18, 20, 23, 25 ± 1, 27, 30, and 33 have been reported by various authors from 26 of the 37 recognized species of Melampodium. A chromosomal survey of 375 plants from 275 different populations suggests that the recorded numbers are stable within the genus and that infraspecific euploidy and aneuploidy are uncommon. These chromosome numbers can be arranged numerically, with morphological and limited cytogenetic substantiation, into four euploid series of x2 = 9, 10, 11, and 12. Of these four groups of species, the x = 10 series is the largest and morphologically most diverse. This consideration, along with additional evidence from the morphology of sterile disc ovaries, suggests that x = 10 is the ancestral chromosomal base in Melampodium. A comparison of morphological and cytological data from the closely related genera, Acanthospermum and Lecocarpus, indicates that the latter are probably on a common base of x = 11. Present day distributional patterns of all three genera support the hypothesis that x = 10 is the ancestral base for the entire complex.     

FLORAL FLAVONOIDS AND ULTRAVIOLET PATTERNS IN VIGUIERA (COMPOSITAE)

Variation occurs among species of Viguiera series Viguiera for ultraviolet (uv) absorption/reflection patterns of ligules. Floral flavonoids that cause uv absorption occur in epidermal papillae. Flavonoids are further localized to the proximal portion of the ligule in the seven taxa that have only proximal uv absorption. Floral flavonoids involved in uv absorption consist of flavone, flavonol, and anthochlor (chalcone/aurone) glycosides. Quercetin 3-methyl ether glycosides characterize the ligules of 10 taxa occurring in Baja California, Mexico, and nearby areas, and these taxa appear to form one taxonomic group. The anthochlor pair, marein/maritimein, characterizes V. dentata, and the lack of ligule flavonoids distinguishes V. potosina from the remaining taxa. The presence of the anthochlor pair, marein/maritimein, only in V. dentata and the lack of ligule flavonoids in V. potosina concur with other data to indicate that these species are not correctly placed with each other or with the other species currently included in series Viguiera.     

GENETIC DIVERGENCE AND GEOGRAPHIC SPECIATION IN LAYIA (COMPOSITAE)

Electrophoretic variability was examined in six species of Layia (Compositae), native to California, which have previously been studied by Clausen, Keck, and Hiesey, and are regarded as a classic example of geographic speciation in plants. The study was carried out to test the hypothesis that the extent of divergence in structural genes coding enzymes is concordant with divergence in morphological characteristics, ecological traits, and reproductive isolation. Eleven enzymes specified by 17 loci were analyzed. The genetic identity values were consistent with those expected on the model that the species diverged gradually as they adapted to geographically separate habitats. Thus, the values between the three species complexes proposed by Clausen, Keck, and Hiesey (L. chrysanthemoides/L. fremontii; L. jonesii/L. leucopappa/L. munzii; L. platyglossa) were substantially lower than the values between species within the complexes. The results provide an important contrast to the very high genetic identities between species which originated rapidly from their progenitors. The electrophoretic results also provided evidence that the cytosolic isozyme of phosphoglucomutase and the cytosolic NADP-dependent isocitrate dehydrogenase in the six species are coded by duplicate genes.     

A STUDY OF MEIOSIS IN HAPLOPAPPUS GRACILIS (COMPOSITAE)

Jackson , R. C. (U. Kansas, Lawrence.) A study of meiosis Haplopappus gracilis (Compositae). Amer. Jour. Bot. 46(7): 550–554. Illus. 1959.—A study of meiosis in the two-paired Haplopappus gracilis has shown that each pair of chromosomes is easily recognized throughout the various stages of meiosis beginning with pachytene. A comparison of mitotic and meiotic chromosomes has been made, and the data indicate that a conspicuous heteropycnotic knob on chromosome B at pachytene is the nucleolar organizer. Other recognizable chromomeres were observed, but additional study is needed before a cytological map can be drawn to show whether regions other than those described on chromosome A and B may be used as markers.     

VARIATION IN CHROMATOGRAPHIC PATTERNS IN THE TRAGOPOGON DUBIUS-PRATENSIS-PORRIFOLIUS COMPLEX (COMPOSITAE)

Natural populations of the diploid species, Tragopogon dubius, T. pratensis and T. porrifolius, the F₁ hybrids of these species, and the two amphidiploids, T. mirus and T. miscellus, were obtained from the same localities used for previous morphological and cytological studies of the evolutionary relationships of this complex. Inter- and intra-populational comparisons were made utilizing 2-dimensional chromatograms of these taxa. Members of the complex shared a group of 18 flavonoid-type pattern components, no one of which was completely species specific. Therefore, species patterns were expressed for a population rather than an individual with pattern components being expressed as a frequency. Patterns for F₁ hybrids and amphidiploids, expressed in the same manner, were relatable to the parental species. Diploid species and F₁ hybrid patterns were the most variable in areas of greatest sympatry, indicating considerable genetic interchange between species. The distribution of specific components in certain populations was interpreted as chemical introgression. Evidence was presented for separate origins of T. mirus in two localities. The results confirm previous interpretations of the evolutionary relationships in this complex, and when compared to those obtained for Baptisia, they implicate the different breeding systems as important factors in establishing the kind of variation observed.     

POLYPLOIDY,DYSPLOIDY, AND CHROMOSOME PAIRING IN ECHEVERIA (CRASSULACEAE) AND ITS HYBRIDS

The 140+ species of Echeveria have more than 50 gametic chromosome numbers, including every number from 12 through 34 and polyploids to n = ca. 260. With related genera, they comprise an immense comparium of 200+ species that have been interconnected in cultivation by hybrids. Some species with as many as 34 gametic chromosomes include none that can pair with each other, indicating that they are effectively diploid, but other species with fewer chromosomes test as tetraploids. Most diploid hybrids form multivalents, indicating that many translocations have rearranged segments of the chromosomes. Small, nonessential chromosomal remnants can be lost, lowering the number and suggesting that higher diploid numbers (n = 30–34) in the long dysploid series are older. These same numbers are basic to most other genera in the comparium (Pachyphytum, Graptopetalum, Sedum section Pachysedum), and many diploid intergeneric hybrids show very substantial chromosome pairing. Most polyploid hybrids here are fertile, even where the parents belong to different genera and have very different chromosome numbers. This seems possible only if corresponding chromosomes from a polyploid parent pair with each other preferentially, strong evidence for autopolyploidy. High diploid numbers here may represent old polyploids that have become diploidized by loss, mutation, or suppression of duplicate genes, but other evidence for this is lacking. Most species occur as small populations in unstable habitats in an area with a history of many rapid climatic and geological changes, presenting a model for rapid evolution.     

INFRASPECIFIC VARIATION OF SESQUITERPENE LACTONES IN AMBROSIA PSILOSTACHYA (COMPOSITAE)

The distribution of fifteen sesquiterpene lactones in sixty-two populations of Ambrosia psilostachya ranging from Canada to Mexico, and cytological observations for seven populations are reported. Chemical data for four Mexican populations of A. cumanensis Kunth are presented. The origin of chemically unique populations of A. psilostachya which occur on the islands and peninsulas that line the Texas Gulf coast are discussed with respect to the chemical, morphological and cytological data.     

ARTIFICIAL HYBRIDIZATIONS IN THE SUBTRIBE PERITYLANAE (COMPOSITAE–HELENIEAE)

Artificial hybridizations were conducted with 37 species of four genera of the subtribe Peritylanae (Compositae). Crossability, pollen stainability, and meiotic behavior were examined for most of the resulting 61 F₁ hybrid combinations. Intergeneric hybrids involving Amauria, Eutetras, Pericome, and Perityle, and infrageneric hybrids involving Perityle were readily obtained. Lower crossability and hybrid fertility were displayed by intergeneric crosses. The infrageneric crosses of Perityle were organized into two categories, intersectional and infrasectional, based upon the taxonomic sections that are recognized for the genus; sect. Pappothrix, sect. Laphamia, and sect. Perityle. In general, the crossability and hybrid fertility of intersectional crosses was markedly higher than that of intergeneric crosses. The results suggest a closer relationship between the three taxonomic sections of Perityle than between Perityle and other genera of the subtribe.     

A CYTOGENETIC ANALYSIS OF CERTAIN POLYPLOIDS IN GRINDELIA (COMPOSITAE)

Two diploid taxa, Grindelia procera and G. camporum, and 3 tetraploid ones, G. camporum, G. hirsutula, and G. stricta, have been studied to ascertain their interrelationships. Meiosis in diploid parental strains was regular, the common chromosome configuration being 5 rod bivalents and 1 ring bivalent. The average chiasmata frequency per chromosome was 0.60. Pollen fertility was about 90% in all strains examined. Diploid interspecific hybrids had normal meiosis with an average chiasmata frequency of 0.56 per chromosome. No heterozygosity for inversions or interchanges was detected, and pollen fertility was above 85%. Meiosis in parental tetraploid strains was characterized by the presence of quadrivalents in addition to a complementary number of bivalents. The average chiasmata frequency per chromosome was 0.59 and pollen fertility was generally about 80%. Tetraploid interspecific hybrids also had quadrivalents, normal meiosis, and high pollen fertility. Close genetic relationships between the diploids and between the tetraploids are indicated, and geographical, ecological, and seasonal barriers to gene exchange exist. Attempts to obtain hybrids between diploids and tetraploids were successful in a few cases. The hybrids were tetraploid and had normal meiosis and fertility similar to parental and F₁ tetraploids. Their origin was by the union of unreduced gametes of the diploid female parent and normal pollen from the tetraploid parent. On the basis of chromosome homology, normal meiosis, plus high fertility exhibited in the diploid, tetraploid, and diploid X tetraploid interspecific hybrids, these species of Grindelia are considered to be a part of an autopolyploid complex. Gene exchange between diploids and diploids, tetraploids and tetraploids, and diploids and tetraploids is possible. Tetraploid G. camporum may have originated by hybridization between G. procera and diploid G. camporum with subsequent doubling of chromosomes and selection for the combined characteristics of the diploids.     

STRUCTURE AND ONTOGENY OF LATICIFERS IN CICHORIUM INTYBUS (COMPOSITAE)

The branched anastomosed laticifer system in the primary body of Cichorium intybus L. originates in embryos from files of laticiferous members at the boundary between phloic procambium and ground meristem. Upon seed germination, laticiferous members develop perforations in the end walls which become entirely resorbed. Perforations also develop in the longitudinal walls of contiguous laticiferous members and from lateral connections between developing laticifer branches. Additional laticiferous members originate as procambium differentiation proceeds, and their differentiation follows a continuous acropetal sequence in leaf primordia of the plumule. In roots, laticifers closely associated with sieve tubes in the secondary phloem originate from derivatives of fusiform initials in the vascular cambium. These laticifers develop wall perforations and in a mature condition resemble laticifers in the primary body. As the girth of the root increases, laticifers toward the periphery, unlike associated sieve tubes, resist crushing and obliteration. Laticifers vary in width from about 4 to 22 μm; the widest ones occur in involucral bracts and the narrowest ones in florets. There was no evidence that intrusive growth occurs during development of the laticifer system, although such growth may occur during development of occasional branches which extend through ground tissue independent of phloem and terminate in contact with the epidermis. Presence of amorphous callose deposits is related to aging of laticifers and mechanical injury.     

PHOSPHOGLUCOMUTASE AND ISOCITRATE DEHYDROGENASE GENE DUPLICATIONS IN LAYIA (COMPOSITAE)

Genetic analysis of isozyme segregation patterns in Layia (Compositae) showed that cytosolic phosphoglucomutase isozymes are encoded by duplicated genes, and that the cytosolic NADP-dependent isocitrate dehydrogenase isozymes are encoded by duplicated genes in species with haploid chromosome numbers of n = 7 and triplicated genes in those with n = 8. The duplicated genes specifying both isozymes assorted independently in all species tested. An electrophoretic survey of phosphoglucomutase in diploid species representing six additional genera of Madiinae, the subtribe to which Layia is assigned, revealed that Achyrachaena, Calycadenia, Hemizonia, Holocarpha, and Madia all possessed duplicated genes. In Lagophylla, one species also had duplicated genes for the isozyme but a second species did not, a loss probably resulting from mutation or chromosomal deletion. The phosphoglucomutase duplication characterizes nearly the entire subtribe and may prove useful to identify phylogenetic relationships between the Madiinae and other subtribes.     

CHROMOSOME NUMBERS IN SOUTH AMERICAN HAPLOPAPPUS CASS. (COMPOSITAE)

Chromosome counts are reported for 33 species from all four sections of the genus Haplopappus in South America. These include first reports for 28 species and two putative hybrids. All chromosome numbers reported herein are 2n = 5_II, with the exception of H. prunelloides with 2_n = 6_II. Unlike the North American species, the morphological diversity of South American taxa is not concomitant with chromosomal variation.     

VARIATION AND LOCALIZATION OF FLAVONOID AGLYCONES IN HELIANTHUS ANNUUS (COMPOSITAE)

Flavonoid aglycone variation within Helianthus annuus, a species widely distributed throughout North America, was analyzed. Flavonoid aglycones of H. annuus consist of two types, flavones and chalcones. The flavone aglycones are sequestered in glandular trichomes that occur on both leaf surfaces, whereas the chalcone aglycones appear to be incorporated in the waxy leaf cuticle. Considerable variation in flavonoid profile was observed with some plants exhibiting as few as one, and others as many as seven of the eight aglycones detected. No definable phytogeographic patterns were observed for this flavonoid variation. Flavonoid aglycone variation also did not differentiate the infraspecific taxa within H. annuus.