Peter W. Fritsch

Phylogeny of Acridocarpus brachylophon (Malpighiaceae) : implications for tertiary tropical floras and Afroasian biogeography

Abstract.— A major tenet of African Tertiary biogeography posits that lowland rainforest dominated much of Africa in the late Cretaceous and was replaced by xeric vegetation as a response to continental uplift and consequent widespread aridification beginning in the late Paleogene. The aridification of Africa is thought to have been a major factor in the extinction of many African humid‐tropical lineages, and in the present‐day disparity of species diversity between Africa and other tropical regions. This primarily geologically based model can be tested with independent phylogenetic evidence from widespread African plant groups containing both humid‐ and xeric‐adapted species. We estimated the phylogeny and lineage divergence times within one such angiosperm group, the acridocarpoid clade (Malpighiaceae), with combined ITS, ndhF, and trnL‐F data from 15 species that encompass the range of morphological and geographic variation within the group. Dispersal‐vicariance analysis and divergence‐time estimates suggest that the basal acridocarpoid divergence occurred between African and Southeast Asian lineages approximately 50 million years ago (mya), perhaps after a southward ancestral retreat from high‐latitude tropical forests in response to intermittent Eocene cooling. Dispersion of Acridocarpus from Africa to Madagascar is inferred between approximately 50 and 35 mya, when lowland humid tropical forest was nearly continuous between these landmasses. A single dispersal event within Acridocarpus is inferred from western Africa to eastern Africa between approximately 23 and 17 mya, coincident with the widespread replacement of humid forests by savannas in eastern Africa. Although the spread of xeric environments resulted in the extinction of many African plant groups, our data suggest that for others it provided an opportunity for further diversification.

High-latitude Tertiary Migrations of an Exclusively Tropical Clade: Evidence from Malpighiaceae

Explanations of tropical intercontinental disjunctions involving South America and Africa typically invoke vicariance of western Gondwanan biotas or long‐distance dispersal. However, many plant groups originated and diversified well after the last direct connection between Africa and South America (ca. 105 million years before the present [mybp]), and it is unlikely that long‐distance dispersal accounts for the distribution of all of these. A less commonly invoked explanation, the boreotropics hypothesis, indicates that some tropical disjunctions arose during the Tertiary via high‐latitude land connections when northern forests supported tropical vegetation. Malpighiaceae are widely distributed across Africa and South America and have been explained as ancient “Gondwanian aborigines” (i.e., vicariants of western Gondwanan biotas) or more recent “American colonists” (i.e., long‐distance dispersalists from South America into the Old World). Fossil and phylogenetic evidence from clock‐independent estimates of molecular divergence times indicate that Malpighiaceae originated in South America during the latest Cretaceous (ca. 68 mybp), in isolation from Africa, and that six amphi‐Atlantic disjunctions within the family occurred during three major episodes: late Paleocene (ca. 60 mybp), latest Eocene–earliest Oligocene (ca. 34–31 mybp), and early Miocene (ca. 21–17 mybp). These age estimates reject a Gondwanan origin for Malpighiaceae, and strict dispersal scenarios ignore paleoclimate, paleoland configurations, and fossil evidence that indicates that the family once inhabited northern latitudes. Instead, these data suggest that Paleocene–Oligocene amphi‐Atlantic disjunct groups in Malpighiaceae moved into North America from South America via the Caribbean Basin, crossed the North Atlantic into Eurasia, and subsequently reached the Old World Tropics during warm intervals when land configurations would have facilitated this migration. Whether Miocene migrations of evergreen thermophilic Malpighiaceae proceeded via northern latitudes or long‐distance dispersal is less clear.

Phylogeny and biogeography of Cercis (Fabaceae): Evidence from nuclear ribosomal ITS and chloroplast ndhF sequence data

Abstract The phylogeny of Cercis (Fabaceae) was estimated with DNA sequences of the nuclear ribosomal ITS region and the 3′ end of the chloroplast gene ndhF. The combined analysis recovers three trees in which a well supported clade of North American and western Eurasian species is nested within a paraphyletic group of Chinese species. In the single most unambiguously resolved topology from these trees, C. canadensis from eastern North America is more closely related to C. siliquastrum from western Eurasia than to C. occidentalis from western North America. DIVA and character optimizations based on this topology suggest that the initial intercontinental divergence events in Cercis involved mesophytic ancestors. Subsequent inferred intercontinental divergence events involving xerophytic ancestors are consistent with the Madrean-Tethyan hypothesis, which postulates an early Tertiary floristic link between the arid regions of western North America and western Eurasia. Calibration of branch lengths with the fossil record suggests that the North American and western Eurasian lineages diverged between 6 and 32 million years ago. The oldest of these values is consistent with both the Madrean-Tethyan hypothesis (>23 million years ago) and dispersion across a North Atlantic land bridge connecting Europe to North America (>13 million years ago), whereas the youngest requires an explanation involving long-distance dispersal. Communicating Editor: John V. Freudenstein

Phylogeny and Biogeography of the Styracaceae

The dicotyledonous family Styracaceae is distributed among all the major Tertiary mixed‐mesophytic forest refugia of the Northern Hemisphere. To infer the biogeographical history of the family and its significance for models of Northern Hemisphere historical biogeography, the phylogeny of the Styracaceae was estimated from separate and combined analyses of three DNA sequence data sets (chloroplast trnL intron/trnL‐trnF spacer, chloroplast rbcL gene, ITS region of nuclear ribosomal DNA) and a morphological data set of 47 characters. Up to 15 samples of other families of Ericales sensu the Angiosperm Phylogeny Group were employed as outgroups. The results strongly support the monophyly of the family. Dispersal‐vicariance analysis and Fitch parsimony optimization support a Eurasian origin of the Styracaceae, with subsequent dispersion to the Americas. This scenario is consistent with a hypothesized European origin for the family based on the fossil record. The eastern Asian–eastern North American disjunct genus Halesia is not supported as monophyletic. The sole Asian species of this genus groups with the Asian genus Rehderodendron, whereas the two North American species most often form parts of polytomies with other genera. The generally nested placement of the warm‐temperate deciduous species of Styrax within the amphi‐Pacific tropical evergreen group is consistent with an initial spread of the genus across the North Atlantic land bridge as part of the Eocene boreotropical flora and subsequent intercontinental dispersion of derived warm‐temperate‐adapted elements.

Phylogeny and infrageneric classification of Symplocos (Symplocaceae) inferred from DNA sequence data

Symplocos comprises ∼300 species of woody flowering plants with a disjunct distribution between the warm-temperate to tropical regions of eastern Asia and the Americas. Phylogenetic analyses of 111 species of Symplocos based on the nuclear ribosomal internal transcribed spacer (ITS) region and the chloroplast genes rpl16, matK, and trnL-trnF yielded topologies in which only one of the four traditionally recognized subgenera (Epigenia; Neotropics) is monophyletic. Section Cordyloblaste (subgenus Symplocos; eastern Asia) is monophyletic and sister to a group comprising all other samples of Symplocos. Section Palura (subgenus Hopea; eastern Asia) is sister to a group comprising all other samples of Symplocos except those of section Cordyloblaste. Symplocos wikstroemiifolia (eastern Asia) and S. tinctoria (southeastern United States), both of subgenus Hopea, form a clade that groups with S. longipes (tropical North America) and the species of subgenus Epigenia. The remaining samples of subgenus Hopea (eastern Asia) form a clade. Section Neosymplocos (subgenus Microsymplocos; Neotropics) is well nested within a clade otherwise comprising the samples of section Symplocastrum (subgenus Symplocos; Neotropics). Section Urbaniocharis (subgenus Microsymplocos; Antilles) groups as sister to the clade comprising Symplocastrum and Neosymplocos. The data support the independent evolution of deciduousness among section Palura and S. tinctoria. The early initial divergence of sections Cordyloblaste and Palura from the main group warrants their recognition at taxonomic levels higher than those at which they are currently placed. An inferred eastern Asian origin for Symplocos with subsequent dispersal to the Americas is consistent with patterns from other phylogenetic studies of eastern Asian-American disjunct plant groups but contrary to a North American origin inferred from the earliest fossil occurrences of the genus.

Phylogeny of Caragana (Fabaceae) based on DNA sequence data from rbcL, trnS-trnG, and ITS

Phylogenetic relationships of 48 species of Caragana (Fabaceae: tribe Hedysareae) and one representative each of Astragalus, Calophaca, Halimodendron, and Hedysarum are estimated from DNA sequences of the rbcL gene, trnS-trnG intron and spacer, and ITS region. At least one representative of all five sections and 12 series within Caragana are included. Analyses yielded strongly supported clades corresponding to sections Caragana, Bracteolatae, and Frutescentes. The species of section Jubatae are distributed among three strongly supported clades, i.e., one with the species of section Bracteolatae, another with two species of section Spinosae, and a third as sister to section Frutescentes. All but the last of these six clades are corroborated by at least one unambiguously traced morphological character. The placement of the other four species of section Spinosae are not well supported and lack unambiguous morphological synapomorphies, and the samples of Calophaca and Halimodendron nest within Caragana with weak support.

Reticulate evolution, cryptic species, and character convergence in the core East Asian clade of Gaultheria (Ericaceae)

Phylogenetic relationships of 84 samples representing 30 species in the core East Asian clade of the wintergreen group of Gaultheria (Angiospermae: Ericaceae: Gaultherieae) were estimated from separate and combined DNA sequence data from five genic regions (ITS, matK, rpl16, trnL-trnF, and trnS-trnG) with parsimony, likelihood and Bayesian analyses. Two major clades were recovered, one comprising several sections and series with leaves generally more than 1 cm long [the ser. Leucothoides sensu lato (s.l.) clade] and another comprising the species of ser. Trichophyllae, with leaves generally less than 1 cm long. The ITS region yielded little phylogenetic resolution, whereas in the combined chloroplast analysis the samples from individual morphospecies in both clades were often nonmonophyletic. This was postulated to result from reticulate evolution in the ser. Leucothoides s.l. clade, particularly in two specific cases of hybridization and a crown clade with likely chloroplast capture following localized introgression. In the ser. Trichophyllae clade, such nonmonophyly was largely attributed to cryptic species and character convergence resulting at least partly from extreme morphological reduction. The relatively low-elevation habitats in which the species of the ser. Leucothoides s.l. clade generally grow are thought to have promoted opportunities for sympatry and reticulation, whereas the high-alpine habitats of ser. Trichophyllae are more likely to have spawned isolated populations and narrow endemism. As in other Sino-Himalayan plant groups, overall low sequence divergence and reticulate evolution suggest rapid radiation in the core East Asian clade of Gaultheria.

Phylogeny of Gaultherieae (Ericaceae: Vaccinioideae) Based on DNA Sequence Data from matK, ndhF, and nrITS

Phylogenetic relationships within the tribe Gaultherieae (Chamaedaphne, Diplycosia, Eubotrys, Gaultheria, Leucothoë, and Tepuia) were examined with DNA sequence data from matK, ndhF, and nrITS. Parsimony analyses were performed in PAUP* for each gene region, combined chloroplast data, and total combined data. A Bayesian analysis was performed in MrBayes on the chloroplast and total combined data sets. The total combined parsimony and Bayesian analyses both strongly support the monophyly of the Gaultherieae and the wintergreen group (Diplycosia, Gaultheria, and Tepuia). Diplycosia is monophyletic and nested within part of Gaultheria. In the Bayesian total combined analysis, Tepuia is strongly supported as sister to a clade containing Gaultheria procumbens, Gaultheria hispidula, Gaultheria leucocarpa var. cumingiana, Gaultheria leucocarpa var. leucocarpa, and all sampled Diplycosia species. Optimization of morphological characters emphasized in classifications of the Gaultherieae onto the molecular phylogeny revealed that (1) fleshy calyces evolved either early in the lineage leading to the wintergreen group or later in two separate clades; (2) capsular fruits are plesiomorphic and berry fruits have evolved independently in Diplycosia and Tepuia and once or twice within a large clade containing all sampled sect. Pernettya members and Gaultheria species not exhibiting a berry fruit; and (3) the ancestral state for both the Gaultherieae and wintergreen group is a racemose inflorescence; solitary‐flowered inflorescences have evolved at least eight times within the Gaultherieae, with several changes back to racemose or fascicular inflorescences.

Phylogeny of Symplocos Based on DNA Sequences of the Chloroplast trnC-trnD Intergenic Region

Abstract Phylogenetic analysis of 74 species of Symplocos was conducted with DNA sequence data from the chloroplast trnC-trnD intergenic region. Maximum parsimony and Bayesian inference trees are consistent with those of a previous study based on combined data from the nuclear ribosomal ITS region and the chloroplast regions rpl16, matK, and trnL-trnF. The inclusion of 21 phylogenetically informative indel characters from trnC-trnD resulted in greater maximum parsimony resolution and clade support than with these characters excluded. A combined five-gene-region (trnC-trnD, ITS, rpl16, matK, and trnL-trnF) analysis based on a data set with complete sequence data is almost completely concordant with that of the combined four-gene data set, and displays higher resolution and overall clade support (in some cases 20 to > 30 bootstrap percentage points). The data indicate monophyly for only one subgenus (Epigenia) and four sections (Barberina, Cordyloblaste, Neosymplocos, and Urbaniocharis) of Symplocos; the other three subgenera (Symplocos, Hopea, and Microsymplocos) and tested sections (Bobu, Palaeosymplocos, and Symplocastrum) will require recircumscription to accord with the principle of monophyly. Supermatrix and supertree analyses were conducted to provide phylogenetic estimates based on all 107 available Symplocos samples with sequence data from at least two of the five gene regions. The supermatrix consensus tree is completely consistent with that from the combined five-gene estimate based on complete sequence data, whereas the supertree consensus differs from these trees in two regions of the topology. The supermatrix consensus also displays greater clade resolution than the supertree consensus. The aligned trnC-trnD data set exhibits a lower percentage of parsimony-informative characters than those based on matK and rpl16 sequences. The length, organization, and relative sequencing ease of trnC-trnD in Symplocos nonetheless confirm the utility of this region for phylogenetic estimation in flowering plants, as previously described.

Multiple Geographic Origins of Antillean Styrax

Abstract The phylogenetic relationships within Styrax series Valvatae were estimated with DNA sequence data from the internal transcribed spacer region of nuclear ribosomal DNA to test hypotheses bearing on the historical biogeography of the Antilles. The results provide evidence for three dispersal events within Styrax to the Antilles, one from southern North America, the other two from South America. The data do not support a strict Greater Antillean vicariance scenario for Styrax. Vicariance between the Greater Antilles and southern North America without immediate prior dispersal would require a more basal position of Styrax ochraceus than that recovered, although low branch support values in the relevant portion of the tree do not preclude this possibility. Dispersal of Styrax from South America to the Greater Antilles could have proceeded across oceanic barriers, or more likely through GAARlandia. Styrax obtusifolius in Cuba and Hispaniola and the strictly South American Foveolaria clade have evolved small flowers and the gynodioecious condition independently. The predominance of microscopic pollinators in the Cuban fauna may have impelled the evolution of small flowers in Styrax obtusifolius. The data suggest that the Antilles have played little if any role in the intercontinental dispersal of Styrax.