James R. Estes

Nectar Fluorescence under Ultraviolet Irradiation

Nectar, which fluoresces in the visible and absorbs in the ultraviolet spectrum when irradiated by ultraviolet light, occurs in many bee-pollinated plants. It is suggested that these characteristics function as direct visual cues by which bees can evaluate the quantities of nectar available. Thus, they assume an important role in pollination of the flowers and foraging efficiency of beers.

Phylogenetic analysis of Artemisia section Tridentatae (Asteraceae) based on sequences from the internal transcribed spacers (ITS) of nuclear ribosomal DNA

Artemisia sect. Tridentatae is composed of 11 species of xerophytic shrubs, which dominate much of western North America. Sequences of the internal transcribed spacers (ITS) of nuclear ribosomal DNA were used to construct a phylogeny, examine circumscription of the section, resolve interspecific relationships, and test competing hypotheses on the origin of the section. The data support the monophyly of sect. Tridentatae, with the exclusion of A. bigelovii and A. palmeri-two historically, anomolous species. However, the ITS data provide insufficient variation to fully resolve interspecific relationships or to support major lineages within the Tridentata clade. Nuclear and chloroplast DNA phylogenies are discordant, which may be a result of interspecific gene flow and subsequent chloroplast capture, particularly related to the placement of A. filifolia and A. californica, in addition to A. bigelovii. Furthermore, the ITS data are in conflict with cpDNA data, providing equivocal evidence for competing hypotheses on the Old World vs. New World origin for the section and do not provide support for definitive subgeneric placement.

Evidence for autoploid evolution in the artemisia ludoviciana complex of the Pacific Northwest

TheArtemisia ludoviciana complex of the Northwest is considered to be an intervarietal autoploid complex on the basis of evidence obtained from cytogenetic analysis. The evidence includes the occurrence of chromosomal races within all but two of the inclusive taxa, the degree and constancy of multivalent formation in the polyploid races, and the high degree of homology among the genomes of the various taxa as demonstrated by the pairing relationships in the F1 progeny.Both triploid and tetraploid progeny were produced in diploid-tetraploid crosses, and the tetraploid offspring were fully as fertile as the natural tetraploids. The triploids, on the other hand, produced very few viable pollen grains. The production of tetraploid offspring in interracial crosses could provide a mechanism for gene flow from the diploid to the tetraploid population.With the observation of both diploid and tetraploid populations ofA. douglasiana, in addition to the well-known hexaploid, a reasonable doubt is cast upon the putative amphidiploid origin of the hexaploid via hybridization betweenA. suksdorfii andA. ludoviciana.

Molecular phylogeny of Artemisia section Tridentatae (Asteraceae) based on chloroplast DNA restriction site variation

Chloroplast DNA restriction site variation was used to examine phylogenetic relationships in Artemisia sect. Tridentatae, a complex of eleven species of woody shrubs, which are dominant components of sagebrush communities of western North America. Twenty-seven endonucleases were utilized to identify 82 variable site mutations, 27 of which were phylogenetically informative. The resulting cpDNA phylogeny indicates that sect. Tridentatae is monophyletic, with the exception of A. palmeri and A. bigelovii, two historically anomolous species. A sister-group relationship between A. palmeri and species of subg. Artemisia supports the exclusion of A. palmeri from sect. Tridentatae (subg. Seriphidium), and its inclusion within subg. Artemisia. Artemisia bigelovii, a species with heterogamous capitula, is nested within the Tridentata clade, supporting its inclusion within the section. Introgression and subsequent chloroplast capture of the Tridentatae genome by two unrelated species, A. californica and A. fihlifolia, may explain the unexpected placement of these two species in the Tridentata clade. Low cpDNA sequence divergence provides only limited resolution of phylogenetic relationships within sect. Tridentatae, indicative of a recently differentiated and/or hybridizing polymorphic species complex. In addition, the cpDNA data provide only equivocal evidence for either of two competing hypotheses regarding the origin and phylogenetic relationship of sect. Tridentatae within Artemisia s.l.

Neotropical Plant Dynamics during the Cenozoic-Diversification, and the Ordering of Evolutionary and Speciation Processes

Previous paleobotanical studies on Tertiary floras from northern Latin America have docu- mented that the lowland tropical rain forest and associated communities underwent significant change in their range and composition during the past 60 Ma. New data from pollen and spore assemblages allow refinement in the nature of these changes in three different geographic regions of the neotropics. At the northern limit in central Mexico through northern Central America, changing climates, particularly fluctuat- ing temperatures, are revealed as a principal force driving vegetation dynamics. In southern Central America (including the proto-Antilles), climatic change had less effect on the vegetation. Rather, there was extensive volcanism and profound, rapid alterations in physiography. In the Amazon Basin there were limited topographic changes and moderate climatic effects. A primary forcing mechanism was fluctuating water tables induced by sea-level changes. It is speculated that these separate histories may have elicited a reordering in the myriad of factors constituting the speciation process and, therefore, provided different mechanisms for achieving biodiversity. An awareness of these separate physiographic provinces with distinct environmental histories may be useful in 1) accounting for geographically correlated genotypic and phenotypic features within a genus; 2) understanding factors that shaped the origin and diversification of individual taxa, and 3) refining scenarios to explain diversity in various parts of the neotropics.

Biosystematic and Phenetic Analysis of Marshallia (Asteraceae)

A phenetic analysis based on morphological features of Marshallia revealed four major clusters of OTUs. These clusters only roughly correspond to the previously recognized species complexes. The most distinct species is M. trinervia, segregated from the remaining species by ovate leaf shape. It is in the same cluster as M. grandiflora, a diploid species closely related to tetraploid M. mohrii. However, M. mohrii also clusters with the Graminifolia-complex, which is composed of M. graminifolia and M. tenuifolia. These latter two species are diploid, morphologically indistinguish- able, and occupy the same bog-like habitat along the Atlantic and Gulf Coastal Plains; consequently M. tenuifolia is treated as M. graminifolia subsp. tenuifolia (Raf.) Watson, comb. et stat. nov. A third cluster is composed of M. obovata and M. caespitosa. The fourth cluster, adjacent to the Graminifolia- complex, includes only M. ramosa. This species was previously thought to be more closely related to M. caespitosa. Morphological variation is continuous among the species, with few abrupt bound- aries. They all occupy specific habitats. In addition, the Graminifolia-complex has diverged in seasonal flowering phenology from the others. All species were cross-compatible at approximately equivalent levels (averaging 15% crossability) with the exception of M. ramosa, a diploid species that possesses a number of chromosomal translocations. Little morphological differentiation has occurred, with ecological divergence and chromosomal evolution more apparent among these species in Marshallia. The extensive intergradation of morphological features among the species may be a result of either: 1) recent isolation with accumulation of few genetic barriers to crossing; or 2) a more ancient divergence with low genetic variation present when the species were initially evolving, followed by little morphological divergence.

Pollination of Cnidoscolus texanus (Euphorbiaceae) in south-central Oklahoma.

The pollination phase in the reproduction of the monoecious Cnidoscolus texanus is primarily nocturnal: pollen and nectar production, peak fragrance emission, and most intense insect visitation to the blossoms all commence with dusk and conclude at dawn. The two principal visitors, the night foraging hawkmoths Hyles lineata and Manduca quinquemaculata, visit both the carpellate and staminate flowers for nectar and carry copious quantities of pollen on their proboscises. Although the plant species is self-compatible, the pattern of flowering for each plant essentially precludes self-fertilization. Therefore the primary mode of reproduction in Cnidoscolus is sphingophilous outcrossing. Bull nettle, Cnidoscolus texanus (Muel. Arg.) Small, is a common plant of sandy wastelands in south-central USA and north-central Mexico. Its floral biology was investigated for three populations of abandoned fields near The University of Oklahoma Biological Station, 2 mi E of Willis, Marshall County, Oklahoma over the summer of 1972. Cnidoscolus texanus, is monoecious with the flowers borne in numerous, terminal cymes. Each cyme includes one, very rarely zero or three, carpellate flowers subtended by 6-12, typically 9, staminate ones. The perianth is 5-lobed and corollalike, and in the staminate flowers, united to form a trumpet blossom (Faegri and van der Pijl 1971) with a tube 14-20 mm deep and a limb of five free lobes 10-16 mm long. The 10 stamens typically are arranged in two numerically equal but morphologically dissimilar and distinct series. The filaments of the inner whorl are basally coalescent and their anthers extend only to the mid-level of the perianth tube. Stamens of the outer whorl are free with the anthers slightly exserted. Occasional plants differ with respect to the numerical distribution of anthers between the series; a few are monadelphous; and finally in some, the central anthers are exserted and the outer series shorter.

Allozyme Variation in Pyrrhopappus multicaulis and P. carolinianus (Asteraceae): Relation to Mating System and Purported Hybridization

The Pyrrhopappus multicaulis complex includes three species of diploid (n = 6) weedy annuals of the southcentral U.S.A. and northern and central Mexico: P. multicaulis, P. geiseri, and P. carolinianus. In the most recent revision, the first two were recognized as partially sympatric varieties of P. multicaulis. To assess genetic variation within and among populations of P. multicaulis s.l. and P. carolinianus, 19 populations have been examined for allozyme divergence at 13 loci. Average pairwise comparisons of genetic identities within P. multicaulis s.l. are 0.914, reflecting an allozyme pattern characterized by minor frequency differences among shared alleles. Morphological and electrophoretic data indicate gene flow among populations in the P. multicaulis complex and do not support recognition of infraspecific taxa. Species rank for P. carolinianus is supported by marked differences in presence and frequency of allozymes compared to P. multicaulis (mean I value of 0.650). The data are not consistent with purported natural hybridization and introgression between these species. Allozyme data are concordant with previous breeding system studies and indicate a mixed mating system in P. multicaulis s.l. and predominant selfing in P. carolinianus. Pyrrhopappus DC. (false dandelion) is a genus

Genetic variation within and among populations of the Marshallia graminifolia complex (Asteraceae)

Abstract The Marshallia graminifolia complex has been variously treated as two distinct species ( M. graminifolia and M. tenuifolia ), and as two subspecies under M. graminifolia . both are diploid and occupy the same bog-like habitats along the Gulf and Atlantic coastal plains of the southeastern United States. Enzyme electrophoresis was used to test various hypotheses of speciational modes and mechanisms in the Graminifolia Complex, including a progenitor-derivative relationship and gradual geographic isolation. Nine enzymes encoded by 16 loci were resolved 13 of which were fixed for the same allele in all population examined. Levels of heterozygosity were low. The mean genetic identity between the two taxa was high ( l = 0.99). There was no evidence for a progenitor-derivative relationship, and no pattern of geographic partitioning of genetic variation among populations. Morphological variation between the two taxa probably results from either simple polymorphism, phenotypic plasticity, and/or clinal variation. Because other congeners of Marshallia share similarly low levels of genetic variation, we believe that its species may have arisen from genetically depauperate ancestors.

A BIOSYSTEMATIC STUDY OF THE RELATIONSHIP OF NAMA HISPIDUM AND NAMA STEVENSII (HYDROPHYLLACEAE)

Biosystematic studies of the morphology, reproductive biology, karyology, and flavonoid composition of Nama hispidum and N. stevensii indicate that the two taxa should be recognized as distinct species. Although the two taxa differ consistently only in the nature of their pubescence, other morphological characters when combined do permit differentiation. The taxa have similar phenological and genetic patterns; both are obligate outcrossers. Nama hispidum is pollinated by halictid bees of the genus Sphecodosoma, whereas N. stevensii is pollinated by the andrenid bee Nomadopsis beamerorum. Both taxa form seven bivalents at meiotic metaphase I, and disjunction is regular. Gene exchange between the two taxa is limited; seed set in interspecific crosses is about 18%. Chromatographic data indicate differences; plants of N. hispidum have an array of four flavonoids, whereas plants of N. stevensii have the same array plus an additional five. It is hypothesized that the widely distributed and variable N. hispidum has given rise to the gypsophilic N. stevensii.