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    ABSTRACT: Aim: Major habitat shifts are well documented for the Hawaiian flora, but examples of shifts to the highest Hawaiian habitats by plant lineages of lowland tropical ancestry have been lacking. We sought to determine whether Hawaiian Artemisia (Compositae—Anthemideae), which includes lowland and subalpine species, represents such an example, by investigating the origin and relationships of the Hawaiian taxa. Location: Hawaiian Islands and continental settings world-wide (except Antarctica and Australia). Methods: Molecular phylogenetic analyses of Hawaiian Artemisia in the context of world-wide diversity were conducted using nuclear and chloroplast DNA spacers. The timing of divergence events associated with inferred dispersals was estimated with calibration from fossil pollen records. Historical biogeographical analyses based on molecular trees and ecological modelling of the distributions of extant taxa were used to aid the interpretation of geographical and habitat shifts associated with diversification and long-distance dispersal. Results: Our findings indicate that the Hawaiian endemic species (A. australis, A. kauaiensis and A. mauiensis) constitute a clade sister to Southeast Asian A. chinensis, which, like the Hawaiian endemics, has ribbed fruit walls and, unlike other members of Artemisia except A. kauaiensis, has a distinct pappus, which is often associated with dispersal ability in Compositae. The clade encompassing A. chinensis and Hawaiian Artemisia was resolved to be most likely of Asian origin. The natural occurrence of A. chinensis in littoral habitats of Taiwan, Okinawa, and the Ryukyu and Bonin islands, and of A. australis in similar settings in the Hawaiian Islands, is likely to reflect the ancestral ecology of the Hawaiian clade, with subsequent colonization of inland, higher-elevation habitats, including subalpine shrubland, where A. mauiensis is endemic. Main conclusions: An ecological shift in Hawaiian Artemisia from tropical coastal habitats to drier and colder subalpine slopes is consistent with evidence from recent studies for repeated colonization of the Arctic by diverse lineages of Artemisia. Artemisia appears to be prone to such anticlimatic ecological shifts, which may explain this exceptional example of an ancestrally lowland tropical lineage in the Hawaiian high-montane flora.
    Full-text · Article · Mar 2013 · Journal of Biogeography
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    ABSTRACT: ARTEMISIA ANNUA produces phytochemicals possessing antimalarial, antitumor, anti-inflammatory, and anthelmintic activities. The main active ingredient, artemisinin, is extremely effective against malaria. Breeding to develop cultivars producing high levels of artemisinin can help meet worldwide demand for artemisinin and its derivatives. However, fundamental reproductive processes, such as the sequence of flowering and fertility, are not well understood and impair breeding and seed propagation programs. Capitulum structure and floral sequence were studied using light and scanning electron microscopy to describe inflorescence architecture, floret opening, and seed set. Florets are minute and born in capitula containing pistillate ray florets and hermaphroditic disk florets. Ray florets have elongated stigmatic arms that extend prior to disk floret opening. Disk florets exhibit protandry. During the staminate phase, pollen is released within a staminate tube and actively presented with projections at the tip of stigmas as the pistil elongates. During the pistillate phase, stigmatic arms bifurcate and reflex. Stigmas are of the dry type and stain positively for polysaccharides, lipids, and an intact cuticle. Floret numbers vary with genotype, and capitula are predominantly composed of disk florets. Both ray and disk florets produce filled seed. Gynomonoecy, early opening of ray florets, and dichogamy of disk florets promote outcrossing in A. annua. For breeding and seed development, flowering in genotypes can be synchronized under short days according to the floral developmental stages defined. Floret number and percentage seed fill vary with genotype and may be a beneficial selection criterion.
    No preview · Article · May 2014 · American Journal of Botany