Evolution and biogeography of the woody Hawaiian violets (Viola, Violaceae): arctic origins, herbaceous ancestry and bird dispersal.

Specialists studying the genus Viola have consistently allied the Hawaiian violets comprising section Nosphinium--most of which are subshrubs or treelets--with putatively primitive subshrubs in certain South American violet groups. Hawaiian violets also possess inflorescences, a floral disposition otherwise found only in other genera of the Violaceae, thus strengthening the hypothesis of a very ancient origin for the Hawaiian species. A survey of phylogenetic relationships among infrageneric groups of Viola worldwide using nuclear rDNA internal transcribed spacer (ITS) sequences revealed a dramatically different biogeographic origin for the Hawaiian violets: A monophyletic Hawaiian clade was placed in a close sister relationship with the amphi-Beringian tundra violet, V. langsdorffii s. 1., in a highly derived position. This remarkable and unforeseen relationship received strong clade support values across analyses, and monophyly of the Hawaiian lineage was further indicated by a unique 26-base-pair deletion in section Nosphinium. The high polyploid base chromosome number (n approximately equal to 40) in the Hawaiian violets relates them to Alaskan and eastern Siberian populations in the polyploid V. langsdorffii complex. More than 50 species of the 260 allochthonous birds wintering in the Hawaiian Islands are found to breed in the Arctic, occupying habitats in which individual birds might have encountered ancestral V. langsdorffii populations and served as dispersers to the central Pacific region. Acquisition of derived morphological traits (e.g., arborescence and inflorescences), significance of a confirmed Arctic origin for a component of the Hawaiian flora, and the likelihood of other "cryptic" Arctic elements in the Hawaiian flora deserving independent molecular phylogenetic corroboration are discussed.

Molecular evolution, adaptive radiation, and geographic diversification in the amphiatlantic family Rapateaceae: evidence from ndhF sequences and morphology.

Rapateaceae (16 genera, approximately 100 species) is largely restricted to the tepuis and sandplains of the Guayana Shield in northern South America, with Maschalocephalus endemic to West Africa. The family has undergone extensive radiation in flower form, leaf shape, habit, and habitat. To analyze the evolution of these distributions and traits, we derived a molecular phylogeny for representatives of 14 genera, based on sequence variation in the chloroplast-encoded ndhF gene. The lowland subfamily Rapateoideae is paraphyletic and includes the largely montane subfamily Saxofridericioideae as a monophyletic subset. Overall, the morphological/anatomical data differ significantly from ndhF sequences in phylogenetic structure, but show a high degree of concordance with the molecular tree in three of four tribes. Branch lengths are consistent with the operation of a molecular clock. Maschalocephalus diverges only slightly from other Monotremae: it is the product of relatively recent, long-distance dispersal, not continental drift--only its habitat atop rifted, nutrient-poor sandstones is vicariant. The family appears to have originated approximately 65 Mya in inundated lowlands of the Guayana Shield, followed by: (1) wide geographic spread of lowland taxa along riverine corridors; (2) colonization of Amazonian white-sand savannas in the western Shield; (3) invasion of tepui habitats with frequent speciation, evolution of narrow endemism, and origin of hummingbird pollination in the western Shield; and (4) reinvasion of lowland white-sand savannas. The apparent timing of speciation in the Stegolepis alliance about 6-12 Mya occurred long after the tepuis began to be dissected from each other as the Atlantic rifted approximately 90 Mya. Given the narrow distributions of most montane taxa, this suggests that infrequent long-distance dispersal combined with vicariance accounts for speciation atop tepuis in the Stegolepis alliance.

Polyphyly and convergent morphological evolution in Commelinales and Commelinidae: evidence from rbcL sequence data.

Phylogenetic relationships of the five families of the order Commelinales remain an area of deep uncertainty in higher-level monocot systematics, despite intensive morphological and anatomical study. To test the monophyly of the Commelinales and the subclass Commelinidae, evaluate their relationships, and analyze evolutionary trends in their morphology, ecology, and biogeography, we conducted parsimony analyses on 95 rbcL sequences representing 17 taxa of Commelinales, 16 taxa of other Commelinidae, and 63 taxa from Arecidae, Liliidae, and Zingiberidae. Commelinales is polyphyletic and Commelinidae paraphyletic, with Eriocaulaceae and Xyridaceae sister to Poaceae and its relatives, Rapateaceae sister to Bromeliaceae and Mayacaceae, and Commelinaceae sister to Philydrales and allies. Thurnia is sister to Prionium at the base of Cyperaceae-Juncaceae; only 1 of Cronquist's multifamily commelinoid orders is diagnosed as monophyletic. We propose a revised Commelinidae, incorporating 4 revised superorders (Bromelianae, Commelinanae, Dasypogonanae, Arecanae) and 10 orders ((Poales, Eriocaulales, Cyperales, Typhales, Bromeliales), (Commelinales, Philydrales, Zingiberales), (Dasypogonales), (Arecales)). Morphological and anatomical characters used to define the original Commelinales and Commelinidae appear to be plesiomorphic or to reflect convergence or recurrent mutation; several characters supporting our revised classification are anatomical traits that seem relatively insulated from environmental selection pressures. The Commelinidae distal to the Arecales arose in South America, with amphiatlantic Bromeliaceae-Mayacaceae-Rapateaceae originating in the Guayana Shield. Ecological diversification involved the repeated invasion of shady, infertile, or arid microsites. The numbers of species in families of the revised Commelinidae are related partly to the extent of adaptive radiation in those families, but seem more strongly related to nonadaptive features promoting speciation, such as restricted seed dispersal (especially in forest interior groups with fleshy fruits), polyploidy, aneuploidy, and apomixis. Species diversity is unrelated to the rate/amount of rbcL sequence evolution.

Consistency, characters, and the likelihood of correct phylogenetic inference.

Computer simulations of character-state evolution in 8, 16, 32, and 64 ingroup taxa with a known set of relationships demonstrate that the maximum probability of correct phylogenetic inference increases with the number of variable (or informative) characters and their consistency index and decreases with the number of taxa, when the consistency index has been standardized to eliminate its dependence on the number of taxa. Equations for the probability of correct phylogenetic inference and for the standardized consistency indices (including or excluding autapomorphies) are derived. Given that actual studies based on DNA restriction sites and sequences generate more characters with a higher level of consistency than comparable studies based on morphology, calculations suggest that such molecular studies may often provide a more precise guide to phylogenetic relationships.

Thorn-like prickles and heterophylly in Cyanea: adaptations to extinct avian browsers on Hawaii?

The evolution of thorn-like structures in plants on oceanic islands that lack mammalian and reptilian herbivores is puzzling, as is their tendency toward juvenile-adult leaf dimorphism. We propose that these traits arose in Cyanea (Campanulaceae) on Hawaii as mechanical and visual defenses against herbivory by flightless geese and goose-like ducks that were extirpated by Polynesians within the last 1600 years. A chloroplast DNA phylogeny indicates that thorn-like prickles evolved at least four times and leaf dimorphism at least three times during the last 3.7 million years. The incidence of both traits increases from Oahu eastward toward younger islands, paralleling the distribution of avian species apparently adapted for browsing. The effectiveness of visual defenses against avian browsers (once dominant on many oceanic islands, based on the vagility of their ancestors) may provide a general explanation for insular heterophylly: the other islands on which this previously unexplained phenomenon is marked (New Zealand, New Caledonia, Madagascar, Mascarene Islands) are exactly those on which one or more large flightless avian browsers evolved.

Chloroplast DNA evidence for the origin of the genus Heterogaura from a species of Clarkia (Onagraceae).

Restriction-site variation in chloroplast DNA was examined in the morphologically distinct and monotypic genus Heterogaura and the related speciose genus Clarkia (Onagraceae), both native to California. Of the 605 restriction sites surveyed, a total of 119 mutations were identified. Of these, 55 were shared by at least two species and were used to construct a most parsimonious phylogenetic tree. This analysis, as well as one based on a distance metric, provided evidence that Heterogaura and Clarkia dudleyana, a member of a phylogenetically advanced section, share a more recent common ancestor than either does with any other species. The two species are more closely related than nearly all paris of Clarkia tested. The origin of Heterogaura from within another genus raises important questions about the adequacy of morphological data and suggests that the relationships of other well-known monotypic plant genera should be reinvestigated.