Correlation between evolutionary history, flowering phenology, growth form and seral status for important veld grasses

Thirty species of veld grasses were analysed for their evolutionary history, flowering phenology, growth form and range of veld types. These characteristics were correlated with successional classes as reported in the literature, and the classes were defined on the basis of the parameters considered. The lowest and highest seral states were clearly distinguished from each other, but there was some overlap between the intermediate class and the highest and lowest classes. Six of the species differed from other representatives of their class. They were either in vegetation types atypical of other species in their group, were known to comprise a number of ecotypes, or were members of hybrid complexes

Atmosphere, ecology and evolution: what drove the Miocene expansion of C4 grasslands?

Grasses using the C4 photosynthetic pathway dominate today's savanna ecosystems and account for ∼20% of terrestrial carbon fixation. However, this dominant status was reached only recently, during a period of C4 grassland expansion in the Late Miocene and Early Pliocene (4–8 Myr ago). Declining atmospheric CO2 has long been considered the key driver of this event, but new geological evidence casts doubt on the idea, forcing a reconsideration of the environmental cues for C4 plant success.Here, I evaluate the current hypotheses and debate in this field, beginning with a discussion of the role of CO2 in the evolutionary origins, rather than expansion, of C4 grasses. Atmospheric CO2 starvation is a plausible selection agent for the C4 pathway, but a time gap of around 10 Myr remains between major decreases in CO2 during the Oligocene, and the earliest current evidence of C4 plants.An emerging ecological perspective explains the Miocene expansion of C4 grasslands via changes in climatic seasonality and the occurrence of fire. However, the climatic drivers of this event are debated and may vary among geographical regions.Uncertainty in these areas could be reduced significantly by new directions in ecological research, especially the discovery that grass species richness along rainfall gradients shows contrasting patterns in different C4 clades. By re-evaluating a published data set, I show that increasing seasonality of rainfall is linked to changes in the relative abundance of the major C4 grass clades Paniceae and Andropogoneae. I propose that the explicit inclusion of these ecological patterns would significantly strengthen climate change hypotheses of Miocene C4 grassland expansion. Critically, they allow a new series of testable predictions to be made about the fossil record.Synthesis. This paper offers a novel framework for integrating modern ecological patterns into theories about the geological history of C4 plants

Variation in important pasture grasses. II. Cytogenetic and reproductive variation.

The chromosome numbers and reproductive variation of seven important pasture grasses from South Africa are compared. This comparison indicates that all these species form polyploid complexes, all reproduce both sexually and either apomictically or vegetatively, and some form of hybridization or cross-fertilization occurs in each species. The ecological success of these species can, therefore, be attributed to the fact that they combine the advantages of polyploidy and apoximis and, at the same time, bypass the disadvantages with their hybridization potential.Keywords: apomixis; cenchrus cilliaris; chromosome number; chromosome numbers; cynodon dactylon; digitaria eriantha; eragrostis curvula; grass; grasses; heteropogon contortus; hybridization; pasture; pasture grasses; polyploidy; setaria sphacelata; south africa; themeda triandra; variatio

Variation in important pasture grasses: I. Morphological and geographical variation.

Seven species are important pasture grasses throughout the western Transvaal, Orange Free State, northern Cape and Natal. Taxonomically, each is a widely distributed species complex with a range of morphological variants and many ecotypes. The local forms well suited to particular environmental conditions are a source of natural variability upon which to base programmes to develop improved pasture strains.Language: EnglishKeywords: cenchrus ciliaris; cynodon dactylon; digitaria eriantha; distribution; ecotypes; environmental conditions; eragrostis curvula; geographical distribution; Geography; grasses; heteropogon contortus; morphological variation; Morphology; natal; northern cape; orange free state; pasture; pasture grasses; setaria sphacelata; south africa; Species; themeda triandra; variability; variants; western transvaa

Names of Southern African grasses: Name changes and additional species reported since 1955.

In the twenty-five years since Chippindall's 'Guide to the Identification of Grasses' in Meredith the Grasses and Pastures of South Africa (1955), which covered about 910 species and subspecific taxa, there have been 227 name changes and 1791 additional species published for southern Africa and accepted by the National Herbarium at the Botanical Research Institute, Pretoria (PRE). The changed names are listed alphabetically both by the currently accepted name and by the old name (synonym). The additional species are also listed alphabetically. The main reasons for changes in botanical names are briefly reviewed, with examples from the lists. At this time, about 1040 grass species and subspecific taxa are recognized in the subcontinent.Keywords: botanical research; botanical research institute; botany; grass; grasses; identification; name change; nomenclature; pastures; southern africa; species; synonyms; taxa; taxonom