Edwin B. Smith

Allozyme divergence and intraspecific variation in Coreopsis grandiflora (Compositae)

Coreopsis grandiflora is an herbaceous perennial occurring primarily in the southeast- ern United States. It is morphologically variable and the variation is accommodated in three diploid (var. grandiflora, var. harveyana, var. saxicola) and one hexaploid (var. longipes) varieties. Populations of the three diploid varieties are usually highly interfertile. An electrophoretic study of 14 soluble enzymes presumably coded by 26 genes revealed no differentiation between any of the varieties. Comparable levels of genetic variation were found in populations of each variety and within each variety as a whole. The high genetic identity between the hexaploid var. longipes and the three diploid varieties suggests that the former is an autopolyploid in the sense that its origin lies exclusively within C. grandiflora. All alleles detected in the hexaploid were also found in the diploids, and no fixed heterozygosity was found at any gene in any population of var. longipes. The electrophoretic evidence is concordant with the high morphological similarity between var. longipes and diploid varieties of C. grandiflora in suggesting an autoploid origin for the former.

ALLOZYME VARIATION IN COREOPSIS NUECENSOIDES AND C. NUECENSIS (COMPOSITAE), A PROGENITOR-DERIVATIVE SPECIES PAIR

Coreopsis nuecensis Heller and C. nuecensoides E. B. Smith are two plant species occurring on the sandy prairies and plains of southeastern Texas (Fig. 1). Although populations of the two species occur in adjacent areas, plants do not grow intermixed in the same populations (Smith, 1974). The only morphological feature consistently distinguishing the two species in the field is that the inner involucral bracts of C. nuecensis are pubescent whereas those of C. nuecensoides are glabrous (Smith, 1974) (Fig. 2). In addition, the stems of C. nuecensis tend to be glabrous while those of C. nuecensoides tend to be pubescent. When grown in the greenhouse, Coreopsis nuecensis is an annual whereas C. nuecensoides persists for two or more years, flowering each season (Smith, 1974; Crawford, unpubl. observ.). However, under natural conditions, the latter species is strictly annual. Coreopsis nuecensoides has chromosome numbers of N = 9 and 10 whereas N = 6, 7 and 8 (7 bivalents and a pair of B chromosomes) are known for C. nuecensis (Turner, 1960; Smith, 1971, 1974; Crawford, unpubl.). Hybrids resulting from crosses between plants within each species, regardless of chromosome number, are highly fertile and it is possible to produce advanced generation hybrids (Smith, 1974; Crawford, unpubl.). By contrast, interspecific hybridization produces vigorous, but almost completely sterile F1 plants (pollen stainability 2-5%). On the basis of cytogenetic evidence, Smith (1974) proposed that Coreopsis nuecensoides gave rise to C. nuecensis by a process of aneuploid reduction. Morphologically, these two species are much more similar to each other than either is to any other species of Coreopsis; indeed, without the differences between their involucral bracts it would be difficult if not impossible to distinguish them. In addition, the two taxa are annuals whereas nearly all others in Coreopsis Section Coreopsis are long-lived herbaceous perennials (Smith, 1974). The present study examined genetic variation within and among populations of the two species to ascertain the amount of genetic divergence between them. Several investigations (Gottlieb, 1973a, 1974; Gottlieb and Pilz, 1976; Rick et al., 1976) have demonstrated that speciation can occur with little or no divergence at gene loci coding for allozymes. By contrast, much higher levels of differentiation at allozyme loci have been detected for most congeneric species (Gottlieb, 1977). Thus, if Coreopsis nuecensoides and C. nuecensis are related as progenitor and recent derivative, then they are expected to exhibit very high similarity at genes coding for enzymes.

Allozyme Divergence Between Coreopsis basalis and C. wrightii (Compositae)

Coreopsis basalis and C. wrightii are diploid, annual plants centered in east and southeastern Texas, with the former introduced into the southeastern United States. The two species are very similar morphologically but are highly intersterile due to differences in chromosome structure. Electrophoresis determined the amount of divergence between the two taxa at 14 genetic loci coding soluble enzymes. Mean genetic identity for ten populations of C. basalis is 0.94 and the value for four populations of C. wrightii is 0.97. Average genetic identity for populations of the two species is 0.92, indicating little if any genetic divergence between the species as compared to conspecific populations. The enzyme data and morphology are con- cordant with the hypothesis that speciation occurred via chromosomal repatterning with minimal divergence at genes coding for isozymes. Isozyme data support the hypothesis that C. basalis and C. wrightii are more closely related to each other than either is to the other two annual species of sect. Coreopsis, C. nuecensoides and C. nuecensis. The mean genetic identities for C. basalis-C. nuecensoides, C. basalis-C. nue- censis, C. wrightii-C. nuecensoides, and C. wrightii-C. nuecensis are 0.77, 0.79, 0.73, and 0.76, respectively.

Coreopsis nuecensis (Compositae) and a related new species from southern Texas

An aneuploid chromosome series ofn = 6, 7, 8, 9, and 10 inCoreopsis nuecensis Heller was analyzed for morphological, distributional, and genetic correlations with the chromosome number classes. The results show that two sets of basic chromosome numbers occur within what has been treated asC. nuecensis: n = 6, 7 andn = 9, 10. Then = 7 class frequently carries a pair of B chromosomes, forming then = 8 class. The base chromosome numbers are correlated with some minor but consistent morphological differences, with distributional differences, and with strong sterility barriers in the F1 hybrids. It is proposed that then = 9, 10 segment be recognized as a new species,Coreopsis nuecensoides.

A biosystematic study of Coreopsis tinctoria and C. cardaminefolia (Compositae)

This paper presents evidence which leads the authors to propose the reduction ofCoreopsis cardaminefolia (DC.) Nutt. to synonymy underC. tinctoria Nutt.Coreopsis cardaminejolia andC. tinctoria overlap morphologically in all characters measured, except for winging vs. non-winging of the achenes. The winging character is shown to be dependent upon segregation at one or two loci. Both “species” have chromosome numbers of 2n = 24 and 2n = 26. The basic number isx = 12, with some plants showing a supernumerary pair of chromosomes, which apparently undergo post-meiotic preferential distribution on both the maternal and paternal sides. The two taxa overlap extensively in range and occupy the same habitat, rather commonly occurring in mixed colonies.Coreopsis tinctoria is redefined to include the intrapopulational variation heretofore designatedC. cardaminefolia.

A cladistic study of North AmericanCoreopsis (Asteraceae: Heliantheae)

A cladistic study of all 44 species of North AmericanCoreopsis was performed using 35 characters. The resulting cladogram indicated that all 11 sections are monophyletic. At the intersectional level, two lineages were revealed, one consisting of six sections occurring almost exclusively in Mexico and California, and another comprising five sections restricted largely to the eastern and southeastern United States. The cladogram is similar to phylogenies produced by less explicit methods but it differs in two major respects: the monotypic sect.Silphidium is placed with other sections from the southeastern United States rather than with Mexican sections, and sect.Anathysana from Mexico is more closely allied with the three California sections than with sect.Electra from Mexico.

EVOLUTIONARY PROCESSES IN THE GENUS COREOCARPUS: INSIGHTS FROM MOLECULAR PHYLOGENETICS

Abstract.— A molecular phylogenetic study of the plant genus Coreocarpus was conducted using nuclear (ITS) and plastid (rpl16 intron) DNA sequences, with phylogenies of the nuclear and plastid sequences highly congruent in defining a monophyletic group of six species (core Coreocarpus), although three other species often placed within the genus were excluded. Relationships within the genus are largely but not totally concordant with prior biosystematic studies. Despite strong molecular support, no morphological characters uniting the six species of core Coreocarpus have been identified; retention of plesiomorphic characters and the genetic lability of characters are two probable factors contributing to lack of consistent defining characters. The age of the core Coreocarpus is estimated at 1 million years because the basal species is endemic to a volcanic island that emerged in the past million years. Mapping the results of earlier breeding studies on the molecular phylogeny showed that use of cross‐compatibility as a criterion for species delimitation would result in the recognition of paraphyletic species. Prior field, morphological, and bio‐systematic studies provided no indication of past hybridization in the evolution of Coreocarpus, and species in the genus appeared to be well defined morphologically. However, three instances of incongruence were observed. Two of these were between the nuclear and plastid partitions, and the third was between the morphological species assignment of one accession and the molecular data. If hybridization accounts for incongruence between the nuclear and plastid data, it occurred between species that now appear to be cross‐incompatible and allopatric. The incongruence between morphological species assignment and the molecular data could be the result of parallel fixation of characters that have a simple genetic basis. This study suggests that the evolutionary history of Coreocarpus is much more complex than indicated from prior biosystematic investigations and that biosystematic and molecular phylogenetic studies may complement each other for elucidating the evolution and phylogeny of a group.

Flavonoid chemistry of Coreopsis grandiflora (Compositae)

The leaf flavonoid chemistryof Coreopsis grandiflora, which includes var.harveyana, var.longipes, var.saxicola and the typical var.grandiflora, is quite uniform with 6-hy-droxyquercetin 7-O-glucoside, luteolin 7-O-glucoside, marein-maritimein chal-cone-aurone pair and lanceolin-leptosin chalcone-aurone pair as consistent com-ponents. Flavonoid data lend support to the hypothesis that the hexaploid var.longipes originated from parents which would be included withinC. grandiflora, i.e., there is no evidence that other species were involved in its formation. One population of var.grandiflora and several collections of var.saxicola contain additional flavonoid components in the form of flavonol 3-O-glycosides. In nearly all instances the additional compounds are attributable to hybridization withC. lanceolata orC. pubescens because these flavonols are characteristic of these two species and morphological considerations also suggest it. Flavonoid chemistry supports the treatment of var.saxicola as a variety ofC. grandiflora rather than as a distinct species.

Leaf flavonoid chemistry of Coreopsis (Compositae) section Palmatae

Examination of leaf flavonoids of all taxa ofCoreopsis sectionPalmatae revealed that most members synthesize an array of common flavone (mostly luteolin and apigenin) glycosides. Each diploid species or diploid member of a species is characterized by a particular ensemble of compounds. These taxa includeC. major, C. verticillata, C. pulchra, C. palmata, andC. tripteris. The latter species differs from all other taxa in producing flavonol (kaempferol and quercetin) glycosides and what appear to be 6-oxygenated compounds. Tetraploids ofC. verticillata exhibit the same flavonoids as diploid members of the species, thus flavonoid chemistry supports the hypothesis that they originated from diploids within the species. Certain populations of hexaploid and octoploidC. major are similar chemically to diploids, suggesting they also originated as intraspeciflc polyploids. Other populations of these polyploids exhibit a flavonoid profile which differs from the profile of the diploids, and this profile is nearly identical to the octoploidCoreopsis × delphinifolia. The latter taxon has been viewed by Smith (1976) and Mueller (1974) as an interspecific hybrid betweenC. verticillata andC. major and/orC. tripteris. Species-specific compounds from the former species occur inC. × delphinifolia but no compounds unique to either of the latter two species are discernable. Flavonoid chemistry is not useful in ascertaining whether either or both species have been involved withC. verticillata in producing plants referable toC. × delphinifolia. There is morphological intergradation between octoploidC. major andC. × delphinifolia, and all plants not appearing to be “pure”C. major exhibit a flavonoid chemistry likeC. × delphinifolia. All plants of sectionPalmatae considered to be alloploids (includingC. × delphinifolia) produce the same array of leaf flavonoids, including several “novel” compounds not expressed in the putative parental taxa. Two of the “novel” flavonoids are present in the geographically restricted diploidC. pulchra. The systematic and phylogentic significance of this is not readily apparent.

Leaf Flavonoid Chemistry of North American coreopsis (Compositae): Intra- and Intersectional Variation

Six classes (flavones, flavonols, C-glycosylflavones, 6-hydroxyflavones, 6-hydroxyflavonols, and 6-methoxyflavones) of foliar flavonoid compounds are the major constituents for 45 species in 11 sections of North American Coreopsis. Sections Calliopsis, Palmatae, and Pseudoagarista are uniform in that all or most species display the same classes of compounds, whereas sections Coreopsis, Eublepharis, Euleptosyne, and Pugiopappus exhibit pronounced interspecific variation. There are general correlations between presence of particular flavonoid classes and three groups of sections in North American Coreopsis. These three groups are viewed as two phyletic lines and a basal primitive group. There is also one monotypic section (Silphidium) of uncertain affinities. One phyletic line centered in the southeastern United States has four sections (Calliopsis, Coreopsis, Eublepharis, Palmatae), which contain a 6-hydroxyflavonol and 6-methoxyflavones; these flavonoid classes are not detected in other sections of North American Coreopsis. The second phyletic line includes sections Tuckermannia, Pugiopappus, and Euleptosyne, which occur primarily in California and contain C-glycosylflavones and 6-hydroxyflavones. The former class of compounds is unknown in the southeastern United States sections, and the latter occurs rarely. Section Silphidium of the southeastern United States has only flavones. Sections Electra, Anathysana, and Pseudoagarista, representing the presumed primitive elements, consist of woody plants occurring in Mexico, and they are more similar chemically to the three sections from California than to plants from the southeastern United States Leaf flavonoid chemistry offers few clues to the origin of the two phyletic lines from the putatively more primitive plants of Mexico.