Jens G. Rohwer

Angiosperm phylogeny based on matK sequence information

Plastid matK gene sequences for 374 genera representing all angiosperm orders and 12 genera of gymnosperms were analyzed using parsimony (MP) and Bayesian inference (BI) approaches. Traditionally, slowly evolving genomic regions have been preferred for deep-level phylogenetic inference in angiosperms. The matK gene evolves approximately three times faster than the widely used plastid genes rbcL and atpB. The MP and BI trees are highly congruent. The robustness of the strict consensus tree supercedes all individual gene analyses and is comparable only to multigene-based phylogenies. Of the 385 nodes resolved, 79% are supported by high jackknife values, averaging 88%. Amborella is sister to the remaining angiosperms, followed by a grade of Nymphaeaceae and Austrobaileyales. Bayesian inference resolves Amborella + Nymphaeaceae as sister to the rest, but with weak (0.42) posterior probability. The MP analysis shows a trichotomy sister to the Austrobaileyales representing eumagnoliids, monocots + Chloranthales, and Ceratophyllum + eudicots. The matK gene produces the highest internal support yet for basal eudicots and, within core eudicots, resolves a crown group comprising Berberidopsidaceae/Aextoxicaceae, Santalales, and Caryophyllales + asterids. Moreover, matK sequences provide good resolution within many angiosperm orders. Combined analyses of matK and other rapidly evolving DNA regions with available multigene data sets have strong potential to enhance resolution and internal support in deep level angiosperm phylogenetics and provide additional insights into angiosperm evolution.

MOLECULAR PHYLOGENETIC ANALYSIS OF THE PERSEA GROUP (LAURACEAE) AND ITS BIOGEOGRAPHIC IMPLICATIONS ON THE EVOLUTION OF TROPICAL AND SUBTROPICAL AMPHI-PACIFIC DISJUNCTIONS

UNLABELLED PREMISE OF THE STUDY The Persea group (Lauraceae) has a tropical and subtropical amphi-pacific disjunct distribution with most of its members, and it includes two Macaronesian species. The relationships within the group are still controversial, and its intercontinental disjunction has not been investigated with extensive sampling and precise time dating. • METHODS ITS and LEAFY intron II sequences of 78 Persea group species and nine other Lauraceae species were analyzed with maximum parsimony and Bayesian inference. Divergence time estimation employed Bayesian Markov chain Monte Carlo method under a relaxed clock. • KEY RESULTS Several traditional genera or subgenera within the Persea group form well-supported monophyletic groups except Alseodaphne and Dehaasia. The divergence time of the Persea group is estimated as ∼55.3 (95% higher posterior densities [HPD] 41.4-69.9) million years ago (mya). Two major divergences within the Persea group are estimated as ∼51.9 (95% HPD 38.9-63.9) mya and ∼48.5 (95% HPD 35.9-59.9) mya. • CONCLUSIONS Persea can be retained as a genus by the inclusion of Apollonias barbujana and exclusion a few species that do not fit into the established subgenera. A major revision is recommended for the delimitation between Alseodaphne, Dehaasia, and Nothaphoebe. We suggest that the Persea group originated from the Perseeae-Laureae radiation in early Eocene Laurasia. Its amphi-pacific disjunction results from the disruption of boreotropical flora by climatic cooling during the mid- to late Eocene. The American-Macaronesian disjunction may be explained by the long-distance dispersal.

Origins and evolution of cinnamon and camphor: a phylogenetic and historical biogeographical analysis of the Cinnamomum group (Lauraceae)

Tropical and subtropical amphi-Pacific disjunction is among the most fascinating distribution patterns, but received little attention. Here we use the fossil-rich Cinnamomum group, a primarily tropical and subtropical Asian lineage with some species distributed in Neotropics, Australasia and Africa to shed light upon this disjunction pattern. Phylogenetic and biogeographic analyses were carried out using sequences of three nuclear loci from 94 Cinnamomum group and 13 outgroup samples. Results show that although there are three clades within a monophyletic Cinnamomum group, Cinnamomum and previously recognized subdivisions within this genus were all rejected as natural groups. The Cinnamomum group appears to have originated in the widespread boreotropical paleoflora of Laurasia during the early Eocene (ca. 55Ma). The formation and breakup of the boreotropics seems to have then played a key role in the formation of intercontinental disjunctions within the Cinnamomum group. The first cooling interval (50-48Ma) in the late early Eocene resulted in a floristic discontinuity between Eurasia and North America causing the tropical and subtropical amphi-Pacific disjunction. The second cooling interval in the mid-Eocene (42-38Ma) resulted in the fragmentation of the boreotropics within Eurasia, leading to an African-Asian disjunction. Multiple dispersal events from North into South America occurred from the early Eocene to late Miocene and a single migration event from Asia into Australia appears to have occurred in the early Miocene.

The timing of nectar secretion in staminal and staminodial glands in Lauraceae

The flowers of many Lauraceae have two kinds of glandular organ: paired glands at the base of the filaments of the third androecial whorl, and staminodes with a glandular head, corresponding to a fourth, sterile androecial whorl. So far, it is unknown why there are two different kinds of organ with apparently the same function. Observations now show that the staminal and the staminodial glands secrete nectar at different times in the heterodichogamous flowering cycle, and are therefore essential for the pollination of bisexual Lauraceae flowers.

Neither Phoebe nor Cinnamomum – the tetrasporangiate species of Aiouea (Lauraceae)

Cinnamomum is among the largest genera of the Lauraceae, including species from tropical to temperate Asia and from tropical to subtropical America. However, previous studies indicated that Cinnamomum might not be monophyletic in its current circumscription. We therefore re-investigated the genus and possible relatives with an increased taxon sample, particularly of the Neotropical species. Our results, based on sequences of the nuclear ITS region and the chloroplast spacers psbA-trnH and trnG-trnS, show that the Neotropical Cinnamomum species indeed do not form a monophyletic group with the Paleotropical species. Instead, the American species form a clade in which most species of the Neotropical genus Aiouea are nested within several subclades. According to the ITS data the Aiouea/Cinnamomum clade is sister to the likewise predominantly Neotropical Ocotea complex, rather than the two Paleotropical Cinnamomum clades. Therefore, Cinnamomum cannot be upheld in its current circumscription. As the type C. verum, is from Asia, the Neotropical species need to be placed in a different genus. We decided to transfer them to Aiouea here, because this is the oldest generic name in the Aiouea/Cinnamomum clade, and the only character separating Aiouea from Neotropical Cinnamomum is the number of pollen sacs per anther (di-vs. tetrasporangiate), a feature that is known to be variable within several other genera as well. This transfer requires 42 new combinations and two nomina nova. In addition, six species described in the unpublished Ph.D. thesis of one of the authors (FLH) are validated in Aiouea here, and the only species of the genus Mocinnodaphne is transferred to Aiouea as well.

Phylogenetic study of the genus Nectandra (Lauraceae), and reinstatement of Damburneya

Earlier studies indicated that the genus Nectandra, currently the second-largest genus of the Neotropical Lauraceae, might be diphyletic in its traditional circumscription, but the evidence was not quite conclusive. Our phylogenetic analyses based on nuclear (ITS) and chloroplast (psbA-trnH) sequences of 45 Nectandra species as well as 42 representatives of 18 genera of the core Lauraceae (Ocotea complex, Laureae, Aiouea, Asian Cinnamomum and Persea groups) confirm the suspicion that Nectandra is diphyletic. The two groups, Nectandra s.str. and the N. coriacea group, are each well supported in the maximum parsimony and Bayesian analyses, but they are not sister to each other. Nectandra s.str. is sister to Pleurothyrium, and the clade including Nectandra s.str. and Pleurothyrium is very likely closer to the dioecious taxa of the Ocotea complex. The N. coriacea group, on the other hand, appears to be closer to bisexual taxa known as the Ocotea helicterifolia group. In addition, Nectandra s.str. is characterized by a large deletion in the psbA-trnH spacer compared to all other core Lauraceae, including its sister group Pleurothyrium. Considering these facts, Nectandra cannot be maintained in the traditional sense. We therefore transfer the species of the N. coriacea group to the oldest generic name applied to this group, Damburneya. On the basis of fossil records from the American subcontinents and in accordance with previous phylogenetic and molecular clock studies we suggest a scenario of a climate-driven migration from North to South America, with a subsequent rapid radiation of Nectandra s.str. in South America.

Nectandra ovatocaudata, a New Species of Lauraceae from Cajamarca, Peru

Abstract.  A new species of Nectandra Rol. ex Rottb. (Lauraceae) from Cajamarca, Peru, is described and illustrated. Nectandra ovatocaudata Rohwer appears to be related to N. amazonum Nees, but differs in its leaf shape, in having a receptacle that is densely pubescent inside, and in its habitat.

A contribution to the pollen morphology of the Cryptocarya group (Lauraceae)

Abstract In this study, pollen grains of 74 taxa (84 specimens) of the Cryptocarya group, including 22 type collections, have been examined by scanning electron microscopy. Pollen grains of Aspidostemon, Endiandra, Hexapora, Potameia and Triadodaphne are described here for the first time. For the other genera (Beilschmiedia, Cryptocarya, Eusideroxylon, Potoxylon) the results of previous studies are largely confirmed, but a novel type of exine covered by clavate-baculate structures was found in a few Cryptocarya species (C. gracilis and C. macrodesme from New Caledonia, C. saligna from South America). A larger diversity of spinule morphology and density than hitherto known is documented among the African species of Beilschmiedia.