Linkages among leaf traits and environment have most often been tested across communities but infrequently within lineages. We studied seven endemic Hawaiian Plantago taxa radiated across elevations, climates, and habitats. We grew plants of six taxa in controlled conditions for 1-2 yr and collected leaves from a seventh in the field. For all taxa, we measured 46 leaf traits and tested hypotheses for trait-environment and trait-trait associations. Because of the rarity of the study plants, our study included low replication within taxa and multiple growth locations; despite these limitations, given reasonable assumptions, our analyses pointed to genetic differentiation among taxa. The leaves of bog taxa were smaller and thicker than those of woodland taxa, with higher leaf mass per area (LMA), stomatal pore area per leaf area, and carbon isotope discrimination (d 13 C). Taxa from higher elevations had thicker leaves and higher LMA, as well as lower nitrogen per mass and higher adaxial stomatal distribution. Taxa of drier sites had higher vein density and d 13 C. Many traits were allometrically related to leaf area, including stomatal density, major vein densities, and xylem conduit numbers and dimensions. Stomatal and xylem traits were correlated, indicating a matching of hydraulic supply and demand. Leaf diversification in Hawaiian Plantago involved coordinated trait shifts, generating strong, apparently adaptive trait linkages.

Insular oceanic islands provide excellent opportunities for the study of evolutionary processes and adaptive radiation. The Hawaiian Plantago radiation comprises six endemic taxa showing considerable inter-and intraspecifi c morphological and ecological diversity. The rDNA internal (ITS) and external (ETS) transcribed spacers and two recently described chloroplast spacers, ndhF -rpl 32 and rpl 32-trnL , were sequenced to study phylogenetic relationships within this morphologically complex group. Phylogenetic analysis provided strong evidence for the monophyly of Hawaiian Plantago , suggesting that the lineage arose from a single long-distance dispersal event. Inconsistencies between nuclear and chloroplast phylogenies suggest a history of hybridization. The basal, unresolved dichotomy of the combined phylogeny is consistent with rapid phenotypic diversifi cation of the major lineages early in the history of this group. Speciation has largely occurred allopatrically, with divergence a result of intraisland ecological shifts between bog and woodland habitats and interisland dispersal events. Most interisland colonizations were from older to younger islands with initial colonization of Kaua ' i. In our analysis, P. pachyphylla is paraphyletic and taxonomic separation of the distinct morphotypes of this species appears justifi ed. Furthermore, the apparent hybrid ancestry and unique morphology and habitat of the endangered P. princeps var. longibracteata support its recognition at the specifi c rank.

Aim The aim of this study was to resolve the phylogenetic placement of island taxa, reconstruct ancestral origins and resolve competing hypotheses of dispersal patterns and biogeographical histories for oceanic island endemic taxa within subgenus Plantago (Plantaginaceae). Location Juan Fernández Islands, the Auckland Islands, Lord Howe Island, New Amsterdam Island, New Zealand, Tasmania, Falkland Islands, Rapa Iti and the Hawaiian Islands. Taxon Island endemics within Plantago (Plantaginaceae), a globally distributed taxonomic group comprising approximately 250 species. Methods We use Bayesian phylogenetic and divergence time analyses and historical biogeographical analysis of molecular sequence data to infer the ancestral origins of the oceanic island species in Plantago . Results Taxa within subgenus Plantago form clades based on geographic proximities and challenge previous phylogenetic relationships and classification based on morphology. We infer that biogeographic histories of oceanic island taxa from multiple islands were shaped by dispersal at different scales and possibly by different types of birds. The highly remote Hawaiian Islands and Rapa Iti were colonized from North American taxa in a pattern corresponding to known migration routes of large marine birds, rather than from New Zealand as previously hypothesized. The island endemics of Juan Fernández, the Falkland Islands, Lord Howe, Auckland Islands and New Zealand are found to have sources in the nearest continental areas. The analyses confirm recent speciation within subgenus Plantago – which is particularly heightened in island lineages in Hawaii and Rapa Iti – but show slightly older divergence times than previous molecular dating studies. Main conclusions Using molecular data to infer ancestral ranges for plants with uncertain taxonomic relationships can greatly improve our understanding of biogeographical histories and help elucidate origins, dispersal modes and routes in widespread lineages with complex distribution patterns such as Plantago . We improve understanding of important floristic exchange areas between continents and islands as a result of long‐distance dispersal. We infer that a combination of both stepping stone dispersal and extreme long‐distance dispersal can shape insular floras, and that multiple floristic areas can be the sources of closely related island taxa. However, despite the successful dispersal of Plantago , radiation in island archipelagos is generally limited suggesting specific traits may limit diversification.

Endemic Hawaiian species in the genus Plantago show considerable morphological and ecological diversity. Despite their variation, a recent phylogenetic analysis based on DNA sequence data showed that the group is monophyletic and that sequence variation among species and morphotypes is low. This lack of sequence polymorphisms resulted in an inability to resolve species and population affinities within the most recently derived clade of this lineage. To assess species boundaries, population genetic structure and interpopulation connectivity among the morphologically and ecologically distinct populations within this clade, genetic variation was examined using eight microsatellite loci. Within-population genetic diversity was found to be lowest in the Maunaiu, Hawai'i population of the endangered P. hawaiensis, and highest in the large P. pachyphylla population from 'Eke, West Maui. Isolation by distance across the range of populations was detected and indicated restricted dispersal. This result is likely to be attributable to few interisland dispersal events in the evolutionary history of this lineage. Genetic differentiation within islands tended to be higher among populations occurring in contrasting bog and woodland habitats, suggesting ecological barriers to gene flow and the potential role of ecological divergence in population diversification. Overall, these results are consistent with findings from phylogenetic analysis of the entire lineage. Our data bring new insights regarding patterns of dispersal and population genetic structure to this endemic and endangered group of island taxa. As island environments become increasingly fragmented, information of this type has important implications for the successful management of these fragile populations and habitats.

The Hawaiian Islands are the only high land in a vast stretch of the North Pacific where past climatological and ecological processes can be reconstructed from terrestrial Earth system archives. We measured hydroclimatic proxies and carbon accumulation in an organic sediment core from the windward montane peatland Pēpē'ōpae on the Island of Moloka'i, Hawai'i using radiocarbon, leaf wax geochemistry, and stable isotopes of carbon and hydrogen in addition to historical pollen records. Following a period of soil development, substantial carbon accumulation began around 10 ka BP (thousands of years before present) under wet conditions. Peat formation was continuous but variable throughout the Holocene, including maxima in carbon accumulation around 9 and 3 ka and a minimum around 1.5 ka that has resulted in a belowground carbon storage today of 144 kg C m −2. From this core we generated a new chronology for previously published pollen spectra from the study site and a Wetness Index that shows increases in dry-adapted taxa in upwind forests during periods of decreased carbon accumulation in the peatland. Shifts in the distribution of sedimentary n-alkane chain lengths in the context of 14 species of modern bog plant n-alkanes suggests litter inputs have been derived from a diverse plant community that changed in dominant species in response to climate. Hydrogen stable isotope ratios of sedimentary C 29 n-alkanes show negative departures around 9 and 3 ka consistent with increases in stormderived rainfall likely related to the position and strength of the northern jet stream. This study is the first to provide a continuous organic sedimentary record of links between hydroclimate, vegetation, and montane belowground carbon sequestration for this part of the North Pacific.