A molecular phylogeny of Panicum (Poaceae: Paniceae): tests of monophyly and phylogenetic placement within the Panicoideae

Panicum L. is a cosmopolitan genus with approximately 450 species. Although the genus has been considerably reduced in species number with the segregation of many taxa to independent genera in the last two centuries, Panicum remains a heterogeneous assemblage, as has been demonstrated in recent years. The genus is remarkably uniform in its floral characters but exhibits considerable variation in anatomical, physiological, and cytological features. As a result, several classifications, and criteria of what the genus should really include, have been postulated in modern literature. The purpose of this research, based on molecular data of the chloroplast ndhF gene, is to test the monophyly of Panicum, to evaluate infrageneric classifications, and to propose a robust phylogenetic hypothesis. Based on the present results, previous morphological and molecular phylogenetic studies, and inferred diagnostic morphological characters, we restrict Panicum sensu stricto (s.s.) to the former subgenus Panicum and support recognition of Dichanthelium, Phanopyrum, and Steinchisma as distinct genera. We have transfered other species of Panicum to other genera of the Paniceae. Most of the necessary combinations have been made previously, so few nomenclatural changes have been required. The remaining species of Panicum sensu lato (s.l.) are included within Panicum incertae sedis representing isolated species or species grouped within monophyletic clades. Additionally, we explore the performance of the three codon position characters in producing the supported phylogeny.     

Reproductive biology of Setaria magna Griseb. (Poaceae: Panicoideae: Paniceae)

The genus Setaria is economically important because many species are cultivated for grains or forage. Setaria magna is an American species, native to North America and introduced in South America. The morphological aspect of this species is similar to S. italica (foxtail millet), suggesting its potential value as a crop. The purpose of this work was to understand the breeding system (self-pollination vs. open pollination) of S. magna; additionally, the floral development was described. The results of the breeding system analysis indicated that S. magna is mainly autogamous and does not appear to have a self-incompatibility mechanism. The floral development observed was similar to that described for other Paniceae; in most of the spikelets only the upper anthecium developed fruit, but a small number of spikelets presented bisexual lower florets. These spikelets produced two caryopses per spikelet. Thus, S. magna can produced two types of dispersal units; a few whitish naked caryopses from the lower anthecium that fall without their lemma and palea at maturity; and a high number of brown caryopses protected by the lemma and palea from the upper anthecium. The presence of a normal embryo sac in the upper anthecium suggests that S. magna would present normal sexual reproduction, although we can not reject the formation of apomitic seeds in the lower anthecium.     

Diversification of inflorescence development in the PCK clade (Poaceae: Panicoideae: Paniceae)

In grasses, inflorescence diversification and its correlation with species evolution are intriguing and not well understood. Part of this problem lies in our lack of comprehension about the inflorescence morphological complexity of grasses. We focused our study on the PCK clade (named for phosphoenol pyruvate carboxykinase), a well-supported monophyletic group for which the relationships among its taxa are not well resolved. Interestingly, the PCK clade has an extensive diversity of adult inflorescence forms. A comparative developmental approach can help us to understand the basis of such morphological differences as well as provide characters that can be used in phylogenetic studies of the group. Using SEM studies, we demonstrate that inflorescence morphology in this clade is even more complex than what is typically observed in adult forms. We describe a number of new characters, and some classical features previously used for taxonomic purposes are redefined on the basis of development. We also define four morphological groups combining adult inflorescence form and development, and we discuss some of the evolutionary aspects of inflorescence diversification in the PCK clade. Taxonomic delimitation among genera in the PCK clade remains confusing and unclear where molecular and morphological studies support different classifications.     

Inflorescence diversity and evolution in the PCK Clade (Poaceae: Panicoideae: Paniceae)

The PCK Clade, represented by six to nine genera, is a monophyletic group situated within the Paniceae tribe. The highly diverse inflorescences within the PCK Clade provide an interesting system for the study of morphological evolution and also may aid in better understanding its unclear systematics. The inflorescence structure of 110 members of the PCK Clade has been investigated. Inflorescences are polytelic showing different levels of truncation. At least 21 different inflorescence subtypes were identified. Fourteen variable inflorescence characters were found, among which some have suprageneric or infrageneric value and others are polymorphic. A key for the identification of inflorescence types is presented. Nine processes have been identified as responsible for inflorescence diversification. Highly branched inflorescences with different internode lengths are present in the basal genus whereas truncated inflorescence morphologies appear late in the history of the clade. The precise timing of morphological changes is impossible to assess until we have a well supported phylogeny for the PCK Clade.     

A new species of Echinolaena (Poaceae: Paniceae) from Ecuador and a key to the New World species of the genus

Echinolaena ecuadoriana sp. nov. from the provinces of El Oro and Guayas in Ecuador is described and compared with E. standleyi . A key to the New World species of Echinolaena is provided, as well as illustration of the inflorescences and spikelets of all the 6 New World species ( E. ecuadoriana, E. gracilis, E. inflexa, E. minarum, E. oplismenoides , and E. standelyi ).     

Abnormal cytokinesis in microsporogenesis of Brachiaria humidicola (Poaceae: Paniceae)

Microsporogenesis was evaluated in the Brachiaria humidicola collection of the Embrapa Beef Cattle Center, represented by 60 accessions. One accession (H121) presented an abnormal pattern of cytokinesis that had never been reported in this genus. Among 900 meiocytes analyzed in the first division, 10.7% underwent precocious and multiple cytokinesis in metaphase I, fractionating the genome and the cytoplasm into two or more parts. The expected cytokinesis after telophase I did not occur. The abnormal meiocytes from the first division entered the second division but the second cytokinesis after telophase II was also abnormal. Among the 857 meiocytes analyzed in the second division, 10.9% presented abnormal, incomplete or total absence of cytokinesis. Dyads and binucleated microspores were recorded among the meiotic products. The use of this accession in the Embrapa breeding program is compromised.     

Atypical foliar anatomy related to Kranz syndrome in Paspalum inaequivalve and Paspalum microstachyum (Poaceae: Panicoideae: Paniceae)

Paspalum L. is a large and complex genus, enclosing more than 300 species, whose boundaries and infrageneric classification are still being studied. Recent phylogenetic analyses suggest that Paspalum inaequivalve Raddi and Paspalum microstachyum J. Presl, from the Inaequivalvia informal group, should be excluded from Paspalum. Focused on the unclear taxonomic position of P. inaequivalve and P. microstachyum, their leaf anatomy was studied, and some atypical features related to C₄ photosynthesis were found. This atypical Kranz syndrome is the aim of this research. Transverse leaf blade sections from fresh and herbarium material of P. inaequivalve were studied by light, fluorescence, and transmission microscopy. Additionally, sheaths and culms of P. inaequivalve and leaf blades of P. microstachyum were observed by light microscopy. δ¹³C isotope discrimination was determinated for P. inaequivalve. We compared our results with available anatomical data from related taxa. As well as typical mesophyll cells (PCA) and mestome sheath cells (PCR), a third type of cells, here called ‘globose parenchymatous cells’, was observed in leaf blades of P. inaequivalve and P. microstachyum. These cells are placed externally to the mestome sheaths of the first and second vascular bundles, they have thin walls, with no developed suberine lamella, few chloroplasts with 1–2 starch grains, thylakoids not organized in grana, and a large central vacuole. The globose parenchymatous cells represent a novel trait in P. inaequivalve and P. microstachyum, further supporting the close relation between both species and their exclusion from the genus Paspalum. This atypical Kranz syndrome has not been described in Paspalum before, but the globose parenchymatous cells here described resemble the distinct cells considered as remnants of the outer parenchymatous sheath described for Anthaenantiopsis, some sections of Panicum L., and Chaetium Nees, providing possible taxonomic significance.     

Exsertion,flowering, and shedding in Panicum maxicum (Poaceae)

Within-panicle flowering, exsertion, and seed ripening were investigated in four clones of P. maximum. Flowering, exsertion, and seed ripening were fast processes (<;10 d for each process). Dates and timing were stable within each clone and should allow definition of the harvest date for each genotype and for each harvest method. Clones showed two main flowering patterns differing in the number of flowered spikelets at the date of maximal flowering and in the time of flowering. Seed set was similar to that of allogamous and anemophilous plants. It was nevertheless lower in clones with a high degree of flowering-shedding overlap. In the absence of flowering-shedding overlap, the time for a panicle to flower and to produce seeds was shorter than the time between two emergences of panicles on a tiller. Reproduction timing seemed controlled to minimize competition between panicles on a tiller.     

Phylogeny and a new tribal classification of the Panicoideae s.l. (Poaceae) based on plastid and nuclear sequence data and structural data

? Premise of the study: The subfamily Panicoideae (Poaceae) encompasses nearly one-third of the diversity of grass species, including important crops such as maize and sugarcane. Previous analyses recovered strong support for a Panicoideae+Centothecoideae lineage within the diverse Panicoideae+Arundinoideae+Chloridoideae+Micrairoideae+Aristidoideae+Danthonioideae (PACMAD) clade, although support for internal relationships was inconsistent. The objectives of this research were to (1) further test the monophyly of each subfamily and previously recovered clades within the Panicoideae+Centothecoideae lineage, (2) establish phylogenetic relationships among these groups, and (3) propose a new tribal classification for this lineage based explicitly on the phylogeny. ? Methods: Maximum parsimony and Bayesian inference analyses of 37 taxa were based on previously published sequences (ndhF and rpl16 intron) and on new plastid and nuclear (rbcL and granule-bound starch synthase I) sequence data as well as structural data. ? Key results. The Panicoideae+Centothecoideae lineage and a majority of the clades identified in previous analyses continue to be robustly supported, but resolution along the backbone of the topology remains elusive. Support for the monophyly of both subfamilies was lacking although support values for some clades increased. The tribes Centotheceae and Arundinelleae were confirmed as polyphyletic. ? Conclusions: Subfamily Centothecoideae is formally submerged into the Panicoideae, and a new tribal classification for the expanded Panicoideae is proposed based explicitly on the phylogeny. This classification includes 12 tribes of which Chasmanthieae and Zeugiteae are segretated from the Centotheceae; Tristachyideae is segregated from Arundinelleae, and a new tribe, Cyperochloeae, is validated to accommodate two isolated genera. A key to the tribes is provided.     

Unusual chromosome numbers in Paspalum L. (Poaceae: Paniceae) from Brazil

Somatic chromosome numbers were determined for 20 new germplasm accessions of Paspalum, belonging to 17 species collected in Brazil. Chromosome number is reported for the first time for P. reduncum (2n = 18), P. cinerascens (2n = 20), P. cordatum (2n = 20), P. filgueirasii (2n = 24), P. ammodes (2n = 36), P. bicilium (2n = 40), P. heterotrichon (2n = 40), and P. burmanii (2n = 48). New cytotypes were confirmed for two germplasm accessions of P. carinatum (2n = 30) and P. trachycoleon (2n = 36), one of P. clavuliferum (2n = 40) and one of P. lanciflorum (2n = 40), indicating variability in these species. The remaining chromosome numbers reported here confirm previous counts. The unexpected chromosome numbers 2n = 18, 24, 36, and 48 in Paspalum species, which are usually shown to be multiples of 10, suggest that much more collection and cytogenetic characterization are necessary to assess the whole chromosomal and genomic multiplicity present in the genus, which seems to be much more diverse than currently thought to be.     

Diversity of inflorescences in the Boutelouinae subtribe (Poaceae: Chloridoideae: Cynodonteae)

The Boutelouinae subtribe is comprised of one monophyletic genus, Bouteloua, with 57 species inhabiting the semi-arid regions of the New World. The inflorescences show significant structural variations, which provides an interesting system to examine their morphological evolution and identify characters and processes that may help to understand the group systematics. The structure of inflorescences was studied in 25 species of Bouteloua. All the species covered under this study have truncated polytelic inflorescences. Structural variations in the inflorescence unit among species may be accounted for by: (1) symmetry of the inflorescence unit, (2) total number of long primary branches, (3) total number of spikelets per branch, (4) number of perfect flowers per spikelet, (5) number of rudimentary flowers, and (6) reproductive system. Homogenization and truncation processes account for the diversity of mature inflorescences that exists in Bouteloua. In this work, we discuss the systematic and taxonomic value of the inflorescence in the Boutelouinae subtribe.     

Arberella (Poaceae: Bambusoideae): A new genus from tropical America

Arberella, a new genus of bambusoid grasses, is established, based on the newly described species,A. dressiert. Also belonging to this new genus are the taxa originally namedOlyra flaccida andRaddia costa-ricensis and several new species from Panama and Brazil which will be described later. The new genus is presented in a key to the genera of the tribe Olyreae, of which it is a member, and a key is given to the three species treated in this paper.     

A molecular phylogeny of the genus Alloteropsis (Panicoideae, Poaceae) suggests an evolutionary reversion from C4 to C3 photosynthesis

Background and Aims: The grass Alloteropsis semialata is the only plant species withboth C₃ and C₄ subspecies. It therefore offers excellent potentialas a model system for investigating the genetics, physiologyand ecological significance of the C₄ photosynthetic pathway.Here, a molecular phylogeny of the genus Alloteropsis is constructedto: (a) confirm the close relationship between the C₃ and C₄subspecies of A. semialata; and (b) infer evolutionary relationshipsbetween species within the Alloteropsis genus. Methods: The chloroplast gene ndhF was sequenced from 12 individuals,representing both subspecies of A. semialata and all four ofthe other species in the genus. ndhF sequences were added tothose previously sequenced from the Panicoideae, and used toconstruct a phylogenetic tree. Key Results: The phylogeny confirms that the two subspecies of A. semialataare among the most recently diverging lineages of C₃ and C₄taxa currently recognized within the Panicoideae. Furthermore,the position of the C₃ subspecies of A. semialata within theAlloteropsis genus is consistent with the hypothesis that itsphysiology represents a reversion from C₄ photosynthesis. Thedata point to a similar evolutionary event in the Panicum stenodes–P.caricoides–P. mertensii clade. The Alloteropsis genusis monophyletic and occurs in a clade with remarkable diversityof photosynthetic biochemistry and leaf anatomy. Conclusions: These results confirm the utility of A. semialata as a modelsystem for investigating C₃ and C₄ physiology, and provide moleculardata that are consistent with reversions from C₄ to C₃ photosynthesisin two separate clades. It is suggested that further phylogeneticand functional investigations of the Alloteropsis genus andclosely related taxa are likely to shed new light on the mechanismsand intermediate stages underlying photosynthetic pathway evolution.     

New combinations for Panicum subgenus Panicum and subgenus Dichanthelium (Poaceae) of the Southeastern United States

Twenty-two new varietal combinations are made for the treatment of the genusPanicum of the Southeastern United States. The following 3 new combinations are made in the subgenusPanicum:Panicum rigidulum var.elongatum, P. rigidulum var.pubescens, P. rigidulum var.combsii. The following 19 new combinations are made in the subgenusDichanthelium:P. strigosum var.glabrescens P. strigosum var.leucoblepharis, P. dichotomum var.roanokense, P. dichotomum var.lucidum, P. dichotomum var.ramulosum, p. dichotomum var.mattamuskeetense, P. dichotomum var.yadkinense, P. ensifolium var.curtifolium, P. chamaelonche var.breve, P. portoricense var.nashianum, P. acuminatum var.fasciculatum, P. acuminatum var.unciphyllum, P. acuminatum var.columbianum, P. acuminatum var.lindheimeri, P. acuminatum var.densiflorum, P. acuminatum varlongiligulatum, P. acuminatum var.leucothrix, P. ovale var.pseudopubescens, andP. ovale var.villosum.