Topic
Wilkesia
About: Wilkesia is a research topic. Over the lifetime, 14 publications have been published within this topic receiving 1679 citations.
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TL;DR: Findings indicate that the internal transcribed spacer region in plants should be further explored as a promising source of nuclear phylogenetic markers.
1,028 citations
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TL;DR: Geologic considerations and the distribution of sporophytic self-incompatibility among these species demonstrate that the tarweed ancestor of the silverswords overcame a dispersal barrier of at least 3900 km of open ocean and the breeding barrier of self- incompatibility.
Abstract: Chloroplast DNA restriction-site comparisons were made among 24 species of the Hawaiian silversword alliance (Argyroxiphium, Dubautia, and Wilkesia) and 7 species of North American perennial tarweeds in Adenothamnus, Madia, Raillardella, and Raillardiopsis (Asteraceae-Madiinae). These data and results from intergeneric hybridization indicated surprisingly close genetic affinity of the monophyletic Hawaiian group to two diploid species of montane perennial herbs in California, Madia bolanderi and Raillardiopsis muirii. Of 117 restriction-site mutations shared among a subset of two or more accessions, more than one-fifth (25 mutations) separated the silversword alliance, M. bolanderi, and Raillardiopsis from Adenothamnus and Raillardella. An additional 10 mutations distinguished the silversword alliance, M. bolanderi, and R. muirii from Adenothamnus, Raillardella, and Raillardiopsis scabrida. Phylogenetic analyses of these data and production of vigorous hybrids of the combinations Dubautia laevigata x R. muirii and (Dubautia knudsenii x Dubautia laxa) x M. bolanderi reinforce and refine Carlquist's hypothesis [Carlquist, S. (1959) Aliso 4, 171-236] that the Hawaiian silversword alliance arose from American tarweeds. Ultimate origin of silversword alliance chloroplast DNA from within the Californian-endemic paraphyletic genus Raillardiopsis was supported with high bootstrap confidence. Geologic considerations and the distribution of sporophytic self-incompatibility among these species demonstrate that the tarweed ancestor of the silverswords overcame (i) a dispersal barrier of at least 3900 km of open ocean and (ii) the breeding barrier of self-incompatibility.
148 citations
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TL;DR: It appears that species may remain genetically similar even after time spans on the order of magnitude of 1,000,000 years, supporting a correlation of increasing genetic distance associated with the time of separation among lineages.
Abstract: The Hawaiian silversword alliance consists of the three genera Dubautia, Argyroxiphium, and Wilkesia, and is a classic example of adaptive radiation in an insular setting. Genetic variation and interspecific genetic differentiation based on ten enzyme loci are described for Dubautia and Wilkesia. Genetic identities among species span the range of values expected from interpopulation comparisons within a single species (I = 0.90-1.00) to those typical of interspecific comparisons (I→=0.67). Genetic-identity values correspond to biogeographic distribution and morphological distinctiveness, supporting a correlation of increasing genetic distance associated with the time of separation among lineages. It may be inferred that the high genetic identities observed within the Hawaiian Madiinae and other island plant groups are due to limited time spans available for taxa to accumulate new genetic variation through mutation. It appears that species may remain genetically similar (I > 0.90) even after time spans on the order of magnitude of 1,000,000 years.
138 citations
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TL;DR: The detailed analysis of the hybrids and parental taxa using cytogenetic, electrophoretic, and molecular approaches has provided compelling evidence that the silversword alliance is a genetically cohesive group whose origin and diversification probably trace to a single colonizing ancestor.
Abstract: The ecological, morphological, and physiological diversity of species in the Hawaiian silversword alliance is exceptional. The 28 species, which belong to the endemic genera Argyroxiphium, Dubautia, and Wilkesia, have a wide variety of geographical distributions and elevational ranges within the archipelago. They grow in habitats as varied as dry scrub and woodland, wet scrub and forest, cinder and lava, and bog. Ecological diversity is also evident among sympatric species. At a site of sympatry on the island of Hawaii, for example, D. ciliolata and D. scabra are restricted to different lava flows, even though individuals of the two species may grow within a meter of one another. The 28 species have growth forms as varied as rosette shrubs, shrubs, trees, and lianas. They have a wide range of leaf sizes and shapes, with the Dubautia species exhibiting significant variation in leaf turgor maintenance capacities. Morphological and physiological diversity is also evident among sympatric species. At a site of sympatry on the island of Maui, for example, A. sandwicense and D. menziesii exhibit different suites of morphological and physiological traits enabling them to cope with the severe environmental conditions. The patterns of diversity and the genomic relationships among the 28 species suggest that a variety of factors may have played important roles in their adaptive radiation. The Hawaiian silversword alliance is a premier example of adaptive radiation in plants (Carlquist, 1980; Carr et al., 1989). The alliance includes 28 species in three endemic genera: Argyroxiphium, Dubautia, and Wlilkesia (Carr, 1985). The species grow in a wide range of habitats and have a wide variety of growth forms. They are also closely related, as evidenced by the high frequency of spontaneous interspecific and intergeneric hybrids in nature, coupled with the ease of production of artificial hybrids in the laboratory (Carr & Kyhos, 1981, 1986). The detailed analysis of the hybrids and parental taxa using cytogenetic, electrophoretic, and molecular approaches has provided compelling evidence that the silversword alliance is a genetically cohesive group whose origin and diversification probably trace to a single colonizing ancestor (Baldwin et al., 1988; Carr et al., 1989). Our objective in this review is to provide insight into the ecological, morphological, and physiological diversity of species in the silversword alliance. With respect to ecological diversity, we compare the geographical distributions, habitats, and elevational ranges of the 28 species, then analyze the local distributions of several sympatric Dubautia species. With respect to morphological and physiological diversity, we compare the growth forms, leaf sizes, and leaf shapes of the 28 species, then examine the turgor maintenance capacities of the Dubautia species and the water and temperature balances of two sympatric Argyroxiphium and Dubautia species. Our primary theme is that the ' This paper is dedicated to Dr. Sherwin Carlquist in honor of his pioneering research on the Hawaiian silversword alliance. The research was supported by NSF Grant DEB-82064 11 and a gift from the Atlantic Richfield Foundation to the senior author. We thank Lani Stemmermann for invaluable companionship, botanical insight, and technical assistance in the field. We also thank the staff of Haleakala National Park, particularly R. Nagata and L. Loope, for critical logistical support, and J. Canfield and N. Friedman for generous photographic assistance. 2 Department of Ecology & Evolutionary Biology, University of Arizona, Tucson, Arizona 85721, U.S.A. < Department of Botany, University of Hawaii, Honolulu, Hawaii 96822, U.S.A. 4 Department of Plant & Soil Sciences, University of Maine, Orono, Maine 04469, U.S.A. Department of Botany, University of California, Davis, California 95616, U.S.A. ANN. MISSOURI BOT. GARD. 77: 64-72. 1990. This content downloaded from 152.1.161.146 on Thu, 27 Mar 2014 19:39:59 PM All use subject to JSTOR Terms and Conditions Volume 77, Number 1 Robichaux et al. 65 1990 Adaptive Radiation of Hawaiian Silversword Alliance
117 citations
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TL;DR: The silversword alliance of the Hawaiian Islands comprises one of the most spectacular arrays of life forms known in a relatively small, clearly natural plant group and shows a truly remarkable spectrum of variation from somewhat herbaceous, low-growing forms through woody shrubs to trees.
Abstract: The silversword alliance of the Hawaiian Islands comprises one of the most spectacular arrays of life forms known in a relatively small, clearly natural plant group. Perhaps the best known member of this alliance is the Haleakala silversword (Argyroxiphium macrocephalum Gray). However, A. macrocephalum is only one of six species in a genus which includes plants called greenswords as well as those called silverswords (cf. St. John, 1973). They ordinarily form large basal rosettes of attractive silver or green leaves for a number of years before they finally produce an elongated inflorescence. Argyroxiphium macrocephalum normally does not branch and dies after producing its massive inflorescence (cf. Kobayashi, 1973a). It is thus, under normal conditions, an essentially herbaceous, monocarpic plant. The floral heads of sword plants are characteristically large (>3 cm) and radiate. Argyroxiphium occurs primarily as a pioneer plant on volcanic pumice or in bogs and is restricted to the islands of Hawaii and Maui. In marked contrast to Argyroxiphium the related endemic genus Dubautia of this alliance (sensu Keck, 1936) is comprised largely of woody, branched shrubs that produce small (<1.5 cm), discoid heads year after year. However, the genus shows a truly remarkable spectrum of variation from somewhat herbaceous, low-growing forms through woody shrubs to trees. Moreover, the recently rediscovered D. latifolia (Gray) Keck from Kauai is a large liana. Altogether there are about 25 species of Dubautia, some of which, like Argyroxiphium may also be found as pioneers on volcanic pumice or in bogs, but others are found in dry forests or in rain forests. Its distribution extends throughout the entire system of major islands from Hawaii to Kauai. A third, related Hawaiian endemic genus, Wilkesia, is comprised of two species, one of which is often monocarpic and produces a rosette of leaves at the summit of a usually unbranched woody stem (cf. St. John, 1971). The second species branches rather freely from the base and presumably flowers repeatedly. The heads of Wilkesia are fairly large and discoid. Wilkesia is found on dry slopes, primarily in Waimea Canyon, only on the island of Kauai. The remarkable array of life forms within the silversword alliance exploits almost every conceivable terrestrial habitat in Hawaii. Its representatives occur from near sea level to timberline and from areas that receive less than 45 cm of annual precipitation to perhaps the wettest place on earth, receiving about 1,300 cm of annual precipitation. These habitats range from very recent lava flows on Hawaii to mature rain forests on Kauai. In spite of the spectacular morphological and ecological diversity exhibited by the members of the silversword alliance, the occurrence of many natural intergeneric, intersubgeneric, and interspecific hybrids (Sherff, 1935, 1944; Kobayashi, 1973b; and Carr, 1978a) attests to the fact that they form a natural, genetically cohesive group that has in all probability resulted from rapid evolutionary differentiation after a single colonization by a progenitor, possibly in less than 10 million years (see Macdonald and Abbott, 1970 for a discussion of Hawaiian geology). Collectively, these plants constitute what may be considered an unparalleled ex-
82 citations