Melissa Luckow

The Rest of the Iceberg. Legume Diversity and Evolution in a Phylogenetic Context

Most readers of a special issue of Plant Physiology on legumes will be familiar with only a handful of species, primarily pea ( Pisum sativum ) and the various economically important “beans” such as soybean ( Glycine max ), and of course, the model legumes Medicago truncatula and Lotus japonicus

Species concepts: assumptions, methods, and applications

The assumptions, methods, and applications of various species concepts prevalent in systematics are reviewed in order to clarify issues and terminology. Species concepts are classified as mechanistic-species as participants in the process of speciation, or historical-species as the end results of processes. Mechanistic concepts lack universality and testability because they rely on a knowledge of how speciation proceeded in any particular case. Historical species concepts are preferred because they can be consistently applied and provide a context in which processes of speciation can be investigated. Three historical species concepts are compared: the Genealogical Species Concept, the Species As Taxa Concept, and the Phylogenetic Species Concept. The Gene- alogical Species Concept supports the recognition of the smallest monophyletic lineages (those that occur at the boundary between reticulating and hierarchical systems of relationship), whereas under the Species As Taxa Concept, hierarchy is considered to occur below the level of species, and any monophyletic unit may be recognized as a species. The problems presented by applying the term monophyly to reticulating systems are discussed as they apply to each concept, as are several problems specific to the Genealogical Species Concept, such as metaspecies. An alternative to mono- phyletic species concepts is the Phylogenetic Species Concept, in which the smallest diagnosable unit is recognized as a species. Monophyly is not considered demonstrable at the species level because, in contrast to Species As Taxa, an assumption of the Phylogenetic Species Concept is that species are basal taxa, and thus mark the level at which hierarchic relationships begin. Finally, the application of species concepts is reviewed by surveying the literature in Systematic Botany and Systematic Zoology/Biology during the past five years. Papers in Systematic Zoology/Biology were generally more explicit about the species concept and the criteria being used to delimit species than were papers in Systematic Botany. Because it is clear that a number of different concepts are currently in use, and these are often distinguished only vaguely, botanists are encouraged to familiarize themselves with the various concepts, and to state explicitly which concepts and criteria are being employed in recognizing species.

Development of nuclear gene-derived molecular markers linked to legume genetic maps

The systematic identification of the orthologous features of related organisms greatly facilitates comparative genomics, including research on genome evolution and comparative genetic mapping. In this study, we selected 274 unique gene sequences for the development of PCR-based genetic markers across fifteen legume genomes, representing six crop or model legume species from the phaseoloid and inverted repeat loss clades (IRLC). DNA sequence analysis demonstrated that 129 of the amplified fragments represented single copy loci across most target diploid genomes. The majority of these markers are intron-spanning (70.5%) and linked to legume genetic maps (85.3%). The markers were grouped into four main categories: (1) intron-spanning relatively conserved, (2) intron-spanning diverged, (3) exon-derived conserved, and (4) exon-derived diverged. The extent of sequence divergence within each category indicates that the corresponding markers may have utility for assessing phylogenetic relationships at different, but overlapping, taxonomic levels. We tested marker performance on genomes that had not been previously sampled, representing 95 different species that span the diversity of the Fabaceae. Phylogenetic analyses support the orthology of amplified sequences, with the notable exception of an ambiguous affiliation of Lotus relative to the IRLC and phaseoloid clades.

Phylogenetic Study of the Genus Piptadenia (Mimosoideae: Leguminosae) Using Plastid Trnl-f and Trnk/Matk Sequence Data

Abstract We undertook a phylogenetic study of the genus Piptadenia with a sample of 18 of ca. 27 recognized species using DNA sequences from the plastid Trnl-F and trnK/matK regions. Parsimony jackknife results support the hypothesis that Piptadenia is polyphyletic and that there are three independent lineages. The largest groups of species form a monophyletic lineage that is sister to Mimosa and corresponds closely to Piptadenia section Piptadenia sensu Barneby. Three species (P. obliqua, P. moniliformis, and P. leucoxylon) of section Pityrocarpa are sister to species of Pseudopiptadenia in a lineage with Parapiptadenia, Microlobius and Stryphnodendron. Piptadenia viridiflora is distantly related to sects. Piptadenia and Pityrocarpa. Section Piptadenia is characterized by the presence of prickles (aculei), a potential synapomorphy linking it to Mimosa, and exserted, racemose or paniculiform inflorescences of aggregated spikes. Piptadenia viridiflora has stipular spines and 1–2 axillary, spicate primary inflorescences. Species of sect. Pityrocarpa are unarmed trees (sometimes with hardened, persistent stipules) whose flowers have recurved petals and an ovary on a long gynophore. We recommend that Piptadenia viridiflora be removed to a new genus, and that Piptadenia be restricted to the other species of sect. Piptadenia. We resurrect the generic name Pityrocarpa to encompass the Pityrocarpa clade and make the following new combinations: Pityrocarpa moniliformis, Pityrocarpa obliqua ssp. brasiliensis, and Pityrocarpa leucoxylon.

LOCATING EVOLUTIONARY PRECURSORS ON A PHYLOGENETIC TREE

Conspicuous innovations in the history of life are often preceded by more cryptic genetic and developmental precursors. In many cases, these appear to be associated with recurring origins of very similar traits in close relatives (parallelisms) or striking convergences separated by deep time (deep homologies). Although the phylogenetic distribution of gain and loss of traits hints strongly at the existence of such precursors, no models of trait evolution currently permit inference about their location on a tree. Here we develop a new stochastic model, which explicitly captures the dependency implied by a precursor and permits estimation of precursor locations. We apply it to the evolution of extrafloral nectaries (EFNs), an ecologically significant trait mediating a widespread mutualism between plants and ants. In legumes, a species‐rich clade with morphologically diverse EFNs, the precursor model fits the data on EFN occurrences significantly better than conventional models. The model generates explicit hypotheses about the phylogenetic location of hypothetical precursors, which may help guide future studies of molecular genetic pathways underlying nectary position, development, and function.

Acacia: The case against moving the type to Australia

Recent studies have shown that Acacia is polyphyletic and must be split into five genera. Proposal 1584 would retypify Acacia : the type of the Australian taxon A. penninervis would be conserved over the current lectotype ( A. scorpioides ) of an African taxon. We disagree with the recommendation of the Spermatophyte Committee to endorse this proposal. Contrary to Article 14.12 of the ICBN, no detailed case against conservation was presented in Proposal 1584. We maintain that there are strong arguments against conservation, such as the large number of countries that would be affected, the economic importance of the extra-Australian species, and the economic burden placed on developing countries. Acceptance of this proposal would also violate the guidelines for conservation which clearly state that the principle of priority should prevail when conservation for one part of the world would create disadvantageous change in another part of the world.

Placing the woody tropical genera of Polygonaceae: A hypothesis of character evolution and phylogeny

UNLABELLED PREMISE OF THE STUDY Taxonomic groups have often been recognized on the basis of geographic distinctions rather than accurately representing evolutionary relationships. This has been particularly true for temperate and tropical members from the same family. Polygonaceae exemplifies this problem, wherein the woody tropical genera were segregated from temperate members of the family and placed in the subfamily Polygonoideae as two tribes: Triplarideae and Coccolobeae. Modern phylogenetic studies, especially when inferred from many lines of evidence, can elucidate more probable hypotheses of relationships. This study builds on previous work in the family and aims to test the traditional classification of the tropical woody taxa, which have been understudied and undersampled compared to their temperate relatives. • METHODS A phylogenetic study was undertaken with expanded sampling of the tropical genera with data from five plastid markers (psbA-trnH, psaI-accD, matK, ndhF, and rbcL), nuclear ribosomal DNA (ITS) and morphology. • KEY RESULTS Results support the placement of nine of 12 genera of the Triplarideae and Coccolobeae within Eriogonoideae, in which these genera form a paraphyletic assemblage giving rise to Eriogoneae. The remaining woody tropical genera excluded from Eriogonoideae occur in the paleotropics. • CONCLUSIONS Traditional characters used to delimit Coccolobeae and Triplarideae are not useful for defining monophyletic groups. The six-tepal condition is derived from the five-tepal condition, and unisexual flowers have arisen multiple times in different sexual systems. Ruminate endosperm has arisen multiple times in the family, suggesting this character is highly plastic.

A survey of anther glands in the mimosoid legume tribes Parkieae and Mimoseae

In a broad survey of anther glands in the mimosoid legume tribes Mimoseae and Parkieae, representatives from 30 genera with anther glands were studied using scanning electron microscopy. Four kinds of anther glands could be distinguished. The Piptadenia-type gland, found in all but four of the genera surveyed, is usually spherical to ellipsoid in shape and often borne on a stipe. The cells making up the gland vary in size among species and are often sculptured. Six different kinds of sculpturing can be recognized: smooth, reticulate, striate, rugulate, scabrate, and papillate. The Gagnebina-type gland is the least specialized, consisting of a simple extension of the connective with irregularly projecting cells. The Prosopis africana-type gland is borne ventrally between the thecae, the connective extending hump-like over the apex of the anther. The Pentaclethra-type gland, found only in the genus Pentaclethra, is distinguished by a median dorsal furrow and a ventral conical structure similar to a food body or osmophore. Anatomical sections revealed two different subtypes within the Piptadenia-type gland. Some glands are composed of a homogeneous matrix of isodiametric cells, whereas others have two layers: a peripheral layer of large radially elongated cells, and a central sphere of smaller isodiametric cells and large air spaces. Some characters of anther glands have clear taxonomic significance, and more detailed surveys within genera will undoubtedly provide additional taxonomic markers.

Conserving Acacia Mill. with a conserved type. What happened in Vienna

This note documents the events and conduct that led to the acceptance of Report 55 of the Permanent Committee for Spermatophyta concerning the conservation of Acacia Mill. with a new type. The procedures followed by the Nomenclature Section of the XVII th International Botanical Congress (IBC) held in Vienna, Austria, in July 2005, are also outlined and briefly described in accordance with the provisions of the International Code of Botanical Nomenclature (ICBN) for dealing with committee reports. This controversial proposal to retypify Acacia Mill. from an African to an Australian type was accepted by the Committee for Spermatophyta, the General Committee, and the Nomenclature Section, a recommendation ratified by the final closing plenary session of the IBC. The ICBN emanating from the XVII th IBC will include Acacia Mill., with a conserved type, in Appendix IIIA Nomina generica conservanda et rejicienda. For those who choose to follow the traditional classification system that applies the name Acacia in a broad sense to a heterogeneous assemblage of species comprising a number of subgenera, this decision holds no implications at generic level. However, should the alternative classification which segregates a broadly defined Acacia into a number of genera be followed, then the name Acacia would apply in a strict sense to the mainly Australian wattles (previously Acacia subg. Phyllodineae-now A. subg. Acacia-of the traditional system.).

The Phylogenetic Affinities of Two Mysterious Monotypic Mimosoids from Southern South America

Abstract Two monotypic genera of Mimosoideae from southern South America, Mimozyganthus and Piptadeniopsis, have been particularly difficult to classify and there has been disagreement about their relationships to other legume genera. We undertook a phylogenetic study based on molecular data from the chloroplast and nucleus, and synthesized it with new data from morphology, cytology, and palynology, in order to determine where these genera belong in the mimosoid phylogenetic tree. Mimozyganthus, an enigmatic genus whose unique morphology led workers to consider it transitional between the subfamilies Mimosoideae and Caesalpinioideae, is instead nested among the higher mimosoids on the molecular tree. Careful evaluation of the characters that were considered to be caesalpinioid-like reveals that they are not identical and are independently derived. Piptadeniopsis is most closely related to Prosopidastrum, a primarily Argentinian genus with lomentiform fruits. This is in close agreement with most morphological characters, although the pollen is different in the two genera. Piptadeniopsis, Mimozyganthus, and Prosopidastrum form a monophyletic group on all molecular trees, a result consistent with vegetative and fruiting morphology, but not floral characters. Although the relationship of this group to other taxa is unresolved in the individual molecular analyses, a combined analysis of all molecular data for a subset of the taxa reveals that the three taxa are more closely related to the Leucaena group than to Prosopis. We hypothesize that the unique floral characters of Mimozyganthus may have evolved in response to pollinator selection, and a pollination study is needed to test this hypothesis.