Pieter Baas

Evolution of xylem physiology

Publisher Summary This chapter summarizes the evolution of wood anatomical traits in woody angiosperms and the recognition of ecological preferences from past geological records for a number of arbitrarily defined wood functional types. Xylem evolution can be viewed in the context of a “trade-off” triangle, with different adaptive solutions to the structure/function problems depending on environmental demands as well as phylogenetic constraints (taxonomic history). Evolution of xylem physiology is complicated by the fact that, ever since the early evolution of land plants, xylem has simultaneously performed multiple functions. Regression analysis of various physiological and anatomical characters is used in the chapter to look for trends and possible “trade-offs” between various extant species. The temporal and spatial distribution of the wood types is largely explained by the “tradeoffs” between xylem conductive efficiency and vulnerability to embolism. The two major causes of embolism in plants appear to be freezing and water stress, but the mechanism for embolism formation differs in these two cases. Regression analysis results provide a basis for understanding the variations in the incidences of vessel diameters as related to freezing and drought. However, additional studies are needed to elucidate the physiological significance of variations in vessel wall thickness, vessel perforation type, wood density and parenchyma distribution. The chapter concludes with a discussion on the ecological patterns in xylem anatomy in terms of their functional significance.

Effects of climate change on biodiversity: a review and identification of key research issues

Current knowledge of effects of climate change on biodiversity is briefly reviewed, and results are presented of a survey of biological research groups in the Netherlands, aimed at identifying key research issues in this field. In many areas of the world, biodiversity is being reduced by humankind through changes in land cover and use, pollution, invasions of exotic species and possibly climate change. Assessing the impact of climate change on biodiversity is difficult, because changes occur slowly and effects of climate change interact with other stress factors already imposed on the environment. Research issues identified by Dutch scientists can be grouped into: (i) spatial and temporal distributions of taxa; (ii) migration and dispersal potentials of taxa; (iii) genetic diversity and viability of (meta) populations of species; (iv) physiological tolerance of species; (v) disturbance of functional interactions between species; and (vi) ecosystem processes. Additional research should be done on direct effects of greenhouse gases, and on interactions between effects of climate change and habitat fragmentation. There are still many gaps in our knowledge of effects of climate change on biodiversity. An interdisciplinary research programme could possibly focus only on one or few of the identified research issues, and should generate input data for predictive models based on climate change scenarios.

Vestured pits: their occurrence and systematic importance in eudicots

The distribution of vestured pits in secondary xylem reveals interesting patterns that may bear on hypotheses of phylogenetic relationships within eudicots. Vestured pits are found to be relatively widespread at the base of the eurosids I, eurosids II, and euasterids I, but the feature probably has been lost or originated independently in several more derived branches of these clades. Vestured pits characterise orders Myrtales and Gentianales sensu APG; other large monophyletic taxa that consistently show vestured pits include Malpighiaceae, Polygonaceae, Brassicaceae, and most Fabaceae. Representatives from euasterids II always show nonvestured pits. The occurrence of the character implies numerous parallel origins in the following divergent, major taxa: (1) Proteaceae, (2) Polygonaceae (Caryophyllales), (3) eurosids I (Zygophyllaceae, Fabales, very few Rosales, Malpighiales), (4) eurosids II (Myrtales, Malvales, Brassicales), and (5) euasterids I (Gentianales, Lamiales, Solanales). It is demonstrated that vestured pits frequently support results from DNA data.

Systematic plant morphology and anatomy-50 years of progress

Fifty years of comparative and systematic plant morphology and anatomy are reviewed. Thanks to new techniques (TEM, SEM, cinematography, molecular analyses), and new methods and concepts (cladistics, evolutionary paleobotany, molecular systematics and molecular developmental genetics), plant systematics and comparative structural studies saw major progress. The integration of micromorphological with molecular data has led to an increasingly robust phylogeny of the angiosperms. Successes and failures in the premolecular era of phylogenetic classification using morphological and/or anatomical markers only are illustrated with examples. With the new phylogenetic framework, it becomes possible to trace the evolution of characters more accurately than before. Central problems in comparative and systematic structural studies are the meaning of homology and character definition; some aspects have been elucidated but new ones have appeared with the molecular dimension in evolutionary biology. In vegetative anatomy, the integration of ecological and systematic anatomy into ecophyletic anatomy has led to a better understanding of the driving forces behind evolutionary diversification of wood and leaf anatomical attributes. However, the intertwining of ecological (extrinsic) and organisational (intrinsic) constraints in the origin of form remains a major challenge for future studies.

Angiosperm wood evolution and the potential contribution of paleontological data

Wood anatomy is often viewed as a source of independent data that may be used to assess evolutionary relationships among angiosperms. Comparative anatomical studies document suites of correlated characters that have been interpreted as general evolutionary trends, of which several have been asserted to be irreversible. Paleobotanical data summarized by Wheeler and Baas provide broad chronological corroboration of some wood anatomical trends, such as evolution from scalariform to simple perforation plates and long to short vessel elements. However, the focus on general evolutionary trends rather than on analyzing character distribution patterns in a cladistic phylogenetic context obscures a more detailed understanding of the evolution of wood anatomical features. Patterns of character evolution, including the assertions of irreversibility, need to be tested through cladistic analyses. In this paper selected wood anatomical features from families of Magnoliidae and “lower” Hamamelididae are summarized and mapped onto previously published cladograms as a preliminary means of testing previous hypotheses of wood evolution. The results show that many of the characters are homoplasious and have evolved both in accord with, and counter to, the hypothesized general trends in different groups of flowering plants. In general, changes that confirm generalized trends are more common than changes that are counter to those trends. Future studies should combine wood anatomical characters with other features as part of a cladistic analysis. Fossil woods have not yet contributed significantly to phylogenetic studies, but in the very few cases where they have been linked to fossil reproductive structures, the woods have provided a better understanding of wood anatomy in early members of some families. Data from fossil wood expand the diversity of anatomical structure known in some angiosperm taxa and thus provide additional evidence that might be used in phylogenetic analyses. Fossil woods have the greatest potential to affect phylogenetic analyses where they can be linked to other fossil organs. The best chance for establishing such a linkage is through the study of fossil charcoalified woods that co-occur with other dispersed mesofossils.

Traditional medicinal plants in Ben En National Park, Vietnam

This paper surveys the medicinal plants and their traditional use by local people in Ben En National Park, Vietnam. A total of 230 medicinal plant species (belonging to 200 genera and 84 families) is used by local people for treatment of 68 different diseases. These include species that are collected in the wild (65%) as well as species grown in home gardens. Leaves, stems and roots are most commonly used either fresh or dried or by decocting the dried parts in water. Women are mainly responsible for health care, they have better knowledge of medicinal plants than men, and also collect them more than men at almost every age level. The indigenous knowledge of traditional medicinal plants may be rapidly lost because 43% of the young generation do not know or do not want to learn about medicinal plants, and the remainder knows little about them. Moreover, nowadays local people tend to use western medicine. Eighteen medicinal plant species are commercialized and contribute on average 11% to the income of the households. The majority of medicinal species are used by less than half of the households and 68% of the medicinal plant species have use indices lower than 0.25. Only 6 of the medicinal species of Ben En are listed in the Red data list of Vietnam, but locally 18 medicinal species are endangered because of overharvesting. A comparison of traditional uses of medicinal plants in Ben En National Park with traditional uses elsewhere in South-East Asia and the Indo-Pacific region shows that the same species may be used for widely different treatments by different ethnic groups. The conservation, sustainable use and economic potential of medicinal plants is discussed. We argue that their use, cultivation in home gardens, and marketing should be encouraged as an affordable alternative to expensive western medicine.

Uses and Conservation of Plant Species in a National Park—A Case Study of Ben En, Vietnam

Uses and Conservation of Plant Species in a National Park—A Case Study of Ben En, Vietnam. This paper surveys the use of wild and cultivated plants by local people in Ben En National Park, Vietnam, and analyzes its impact on the conservation status of some of the utilized species. A total of 208 species used for a range of nonmedicinal purposes are listed. See Hoang et al. (2008a) for 230 medicinal plants used in the park. Most species are used for food. The use of plants contributes very significantly to the livelihood of local people in the park, but the current use patterns are not sustainable and would lead to local extinction of rare and endangered species if no additional conservation measures are introduced. Men collect nonmedicinal plants more often than women. A total of 38 useful plant species are commercialized, and contribute 12% of the average income of individual households. Bamboo shoots of Schizostachyum funghomii (Poaceae) are the most important for income generation. The monetary equivalent of noncommercialized useful plants probably far exceeds the value of the traded plant products. Plant use is independent of the ethnicity of the different populations living in the park. Larger households make use of a greater variety of useful plant species than small families. Abundant species in the forest have a higher use index (UI) than less common species. Out of the 208 useful species, as many as 27 were found to be endangered locally, many more than the 11 or 8 endangered species included in national or global red lists. Currently, useful plants, especially important timber trees, are more abundant in the less disturbed parts of the park, far away from the villages, indicating the pressures of illegal logging and harvesting near villages on the ecosystems.

Vestured pits in Malvales s.l.: a character with taxonomic significance hidden in the secondary xylem.

The distribution of vestured pits in the secondary xylem of all major groups of Malvales s.l. is investigated and compared with recent circumscriptions and phylogenetic insights of the order. While the monophyly of the core Malvales, including Bombacaceae, Malvaceae s.str., Sterculiaceae, and Tiliaceae, is supported by the lack of vestured pits, the character is consistently present in three malvalean alliances that are well supported based on molecular data: (1) Bixaceae, Cochlospermaceae, and Diegodendraceae; (2) Cistaceae, Dipterocarpaceae s.l. (including Monotaceae), and Sarcolaenaceae; and (3) Thymelaeaceae s.l. (including Aquilariaceae and Gonystylaceae). Vestured pits are absent in other malvalean taxa such as Petenaea, Muntingiaceae, Neuradaceae, and Sphaerosepalaceae. Families that are now excluded from the order, such as Dirachmaceae, Elaeocarpaceae, and Huaceae also have non-vestured pits. Rudimentary vestures in Plagiopteraceae, however, do not necessarily indicate a malvalean affinity.

Vegetative Anatomy and Affinities of Dirachma socotrana (Dirachmaceae)

Abstract Stem and leaf anatomy of Dirachma socotrana, an endemic species from Socotra, is described in detail. The diffuse porous to semi-ring-porous wood is characterized by solitary vessels and vessels in short radial multiples with a tendency for oblique/radial vessel arrangement, simple vessel perforations, vascular tracheids, nonseptate fibers with simple to minutely bordered pits mainly confined to radial walls, axial parenchyma which is scanty paratracheal and in 1–2-seriate marginal bands, and mainly 1–2-seriate heterocellular rays. The inner bark shows stratified fiber groups; the outer bark has flaring rays. The dorsiventral leaves typically have an indumentum of small, unicellular hairs, anomocytic stomata, an adaxial epidermis largely composed of periclinally divided mucilage cells. The petiole and midrib vascular bundle is typically composed of a simple arc-shaped strand. Prismatic crystals are common in the wood, bark, pith, and leaf. The systematic position of the monotypic family Dirachmaceae in a newly defined Rosales sensu Angiosperm Phylogeny Group was established recently on the basis of molecular data and confirmed by ovule and seed characters. Vegetative anatomical features provide additional arguments for a placement of the family within this order, particularly close to the Rhamnaceae. Communicating Editor: Paul Wilson