Examination of literature shows that a number of authors regard outbreeding and heterozygosity as the prevalent factors associated with long-term successful evolution in the angiosperms. A number of plant evolutionists, however, have doubted the truth of such an assumption. Ever-increasing reports of the existence of arboreal angiospermous apomixis in tropical forests of the Neotropics and the Far East undermined a thinking which, recently, has rested on optimality. Finding apomixis in trees surprised authors, who held biased opinions about the determinism of outbreeding as the major guiding factor in the evolutionary history of the angiosperms. The thinking that apomixis may turn out to be a regular mating system of the flowering plants met with the approval of some authors, who wondered about the true penetration of the phenomenon among the higher plants. The fact that one-third of all known flowering plants are autogamous has cast further doubt on the deterministic infallibility of outbreeding and successful long-term evolution. Despite claims that the breeding system is directly involved with fitness, while determining the course of optimized evolution, there is comparatively little hard evidence to substantiate a hypothesis which, in the last analysis, has rested principally on common sense. Rather, if continuing field research happens to unveil new cases of woody angiospermous apomixis, a prediction is advanced that the next two biomes to show regular incidence of the phenomenon are Africa's paleotropical savannas and humid forests. If evolution is partly or wholly dependent on the breeding system to proceed, current knowledge supports views that further enhancement of organic diversification vis-à-vis selection and adaptednesss rests on three major tested mating systems: outbreeding, inbreeding and apomixis.

This article provides a review of studies concerning the floristics, vegetation description and ecology of the ultramafic (serpentine) soils of Tuscany, central Italy. After a concise history of geobotanical research on Tuscan ultramafic outcrops since the end of sixteenth century, the features of the flora are summarized. The most significant vegetation types are concisely described and their ecology discussed in the following section. The role of soil nickel toxicity in limiting vegetation development is reconsidered and appears less important than are drought and nutrient stress. Drought stress also has a special role during exceptionally dry summers, which can occasionally occur and significantly reduce vegetation structure by causing the local extinction of many late-successional species. Nutrient-addition experiments and permanent plot monitoring provided additional evidence supporting the drought and nutrient stress hypothesis. The last section of this article discusses the main threats to the conservation of the unique plant diversity of Tuscan ultramafic environments, the most significant of which are quarrying and pine plantations. Pine plantations, mostly established for soil amelioration and erosion control, determine not only the increase in vegetation cover and diversity but also a trend for serpentine endemic and rare species to disappear.

The Temperate Broad-Leaved Evergreen Forest (TBEF) zone is centered in peninsular Florida. It is characterized by mainly nontropical taxa that form an evergreen dicot forest, often with a Sabal palm in the canopy, in which deciduous dicot trees are present but rarely become local dominants. The Madrean-Tethyan floristic affinities of this life zone are briefly discussed, as is plant endemism, and a recommendation is given for recognizing it as a separate phytochorion, the Central Floridian Subprovince, in the Atlantic and Gulf Coastal Plains Province of southeastern North America. Also recommended for separate status is the Apalachicolan Subprovince, in the panhandle of Florida and adjacent Georgia and Alabama. These recommendations follow an earlier recognition of the floristic uniqueness of both areas (Greller, 2000). Three physiographical regions in the TBEF are recognized: Peninsular Florida (including the Atlantic and Gulf Coastal regions); the Atlantic Outer Coastal Plain, Sea Islands and Outer Banks; and the Gulf Coastal Shores, Islands, Prairies and Marshes (from panhandle Florida west to Louisiana and Texas). Following Heinrich Walter's zonobiome classification system, one zonobiome and two zonoecotones are recognized for the TBEF region. Following a literature review, a classification of TBEF ligneous, mainly arborescent, vegetation types is given. The article ends with brief discussions of some lowland and a number of montane arborescent vegetation types of the Greater Antilles and of Baja California related to TBEF flora and vegetation.

The Poaceae family has been reported in several published works to show evidence of allelopathic activity. Secondary metabolites as phenolic compounds, hydroxamic acids, flavonoids, etc. commonly occur in both cultivated and wild Gramineae. This article, therefore, attempts to review and synthesize past and recent findings concerning the allelopathic activity of this family. It reviews the type of the activity (stimulative or inhibitive), the donor plant, the target species, and the mode of action in each case.