African Journals OnLine
South African Journal of Botany

VOLUME 67 ISSUE 4 (2001)

South African Journal of Botany 67 (4) 2001, 497-505

©2001 NISC Pty Ltd, www.nisc.co.za

Minireview

Abscisic acid biosynthesis in vascular plants is a constitutive process

AK Cowan

e-mail: [email protected]

Received 24 August 2001, accepted in revised form 27 August 2001

The biosynthetic pathway leading to the formation of the plant hormone abscisic acid (ABA) in plants exposed to stress is believed to involve dioxygenase-mediated cleavage of a 9'-Z-xanthophyll followed by oxidation of the product xanthoxal (XAN) via abscisic aldehyde (AB-ald). However, there are inconsistencies in the current model. Use of ABA-deficient mutants has not adequately explained the origin of basal endogenous ABA. The ubiquitous occurrence of AB-ald as a natural plant product has not been unequivocally established, its conversion to ABA in vivo and in vitro occurs at rates below 30%, and the relationship between AB-ald and 2-trans-abscisic alcohol (trans-AB-ol) has not been wholly elucidated. This review explores the constitutive nature of ABA biosynthesis. Schemes accounting for the metabolism of XAN and 2-trans-AB-ol are proposed. It is concluded that there exist two precursor pools viz., β,β-carotenoids, and E,E- and E,Z-farnesol. These precursors are converted to ABA via 4'-keto-xanthoxic acid and 2-trans-AB-ol respectively presumably after incorporation into, and 'stress-induced' release from, ABA-adduct.

South African Journal of Botany 67 (4) 2001, 506-519

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The vegetation of ash disposal sites at Hendrina power station I: Phytosociology

TL Morgenthal¹*, SS Cilliers¹, K Kellner¹, H van Hamburg¹ and MD Michael²

1 School for Environmental Sciences and Development, Potchefstroomse Universiteit vir Christelike Hoër Onderwys, Potchefstroom 2520, South Africa

* Corresponding author, e-mail: [email protected]

Received 12 July 2000, accepted in revised form 11 January 2001

A phytosociological study was conducted as an initial assessment of the vegetation on ash disposal sites to determine the community structure of vegetation and how the communities were related based on their species composition and habitat characteristics. The Braun-Blanquet survey and data analysis method was used to identify and classify plant communities on ash disposal sites and an adjacent natural grassland. Relevés were compiled in 113 survey plots. The TWINSPAN classification algorithm was used as first approximation and results were subsequently refined using Braun-Blanquet procedures. The DCA ordination technique was also used to determine the relationship between communities and whether gradients exist in the study area. α-diversity between communities are statistically compared using the Shannon diversity indices and species richness. The natural grassland sites, rehabilitated ash disposal sites and unrehabilitated ash disposal sites formed three separate communities. The two sub-communities that are described on rehabilitated ash disposal sites are distinguished mainly with respect to age of rehabilitation and level of disturbance. Community structure, on a variant level, is largely determined by different treatments (seed mixtures and soil preparations) that were used in the rehabilitation of the ash disposal sites. Plant communities on recently rehabilitated sites are similar to plant communities on dumps of domestic refuse on some of the disposal sites. Based on the variants described, three homogenous areas on the old rehabilitated sites, which were rehabilitated more than three years ago, can be identified. Vegetation is relatively homogenous and variants are closely related. Differences in rehabilitation treatment, age of rehabilitation and man-made disturbances were some of the important factors determining the establishment of different communities on ash disposal sites. Statistically significant differences are found in the diversity of vegetation studied on a community and variant level. Associations on the ash disposal areas are strongly based on the dominance of particular species rather than specific indicator species.

South African Journal of Botany 67 (4) 2001, 520-532

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The vegetation of ash disposal sites at Hendrina Power Station II: Floristic composition

TL Morgenthal¹*, SS Cilliers¹, K Kellner¹, H van Hamburg¹ and MD Michael²

1 School for Environmental Sciences and Development, Botany, Potchefstroomse Universiteit vir Christelike Hoër Onderwys, Potchefstroom 2520, South Africa

* Corresponding author, e-mail: [email protected]

Received 12 July 2000, accepted in revised form 11 January 2001

An important component of any ecosystem is the species it contains. Species also serves as good indicators of the ecological condition of a system. A list of all species collected during the three-year period was therefore compiled together with their life form spectra. The floristic composition of the ash disposal area at Hendrina Power Station was also compared with the floristic composition of an adjacent natural grassland. A total of 278 species were identified of which 151 occurred on the ash disposal sites and 163 in the natural grassland. Of all the species, 35 occurred in both areas of which most were annual pioneer species. The species composition and life form spectra of the two areas were considerably different. Therophytes were, for example, more abundant on the ash disposal areas. The reconstruction of an ecosystem on ash disposal sites with a species composition similar to that of the natural grassland will require far more financial inputs and habitat amelioration than is presently the situation.

South African Journal of Botany 67 (4) 2001, 533-539

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The effectiveness of post-fire soil disturbance in restoring fynbos after alien clearance

PM Holmes¹* and W Foden²

* Corresponding author, email: [email protected]

Received 20 March 2000, accepted in revised form 12 February 2001

The control of invasive alien plants is one of the major tasks facing conservation managers of South African fynbos vegetation. Extensive clearance work currently is underway, but the ultimate success of these operations depends upon good indigenous vegetation recovery. Fynbos species potentially may recruit from persistent seed banks in the soil, but surface seed banks may become depleted under dense aliens and deeper seed banks may fail to germinate. In this study, the effect on fynbos recovery of disturbing the soil mechanically, to a depth of 100—150mm, following alien clearance, was investigated. It was hypothesised that soil disturbance would promote germination from persistent, soil-stored seed banks. It was further hypothesised that soil disturbance would have a greater effect following high compared to low fire intensities. Soil disturbance had no effect on total plant recruitment. There was a significant negative relationship between fire intensity and plant density two years post-fire. Recruitment levels at the study site were low compared to those at sites invaded for two to three decades. This indicates that fynbos seed persistence may decline rapidly after four decades of burial. Soil disturbance resulted in higher indigenous species richness and projected canopy cover at the final census, two years post-fire. Changes to guild structure following soil disturbance included an increase in the cover of shrubs relative to graminoids and forbs, and small-seeded species relative to larger-seeded myrmecochorous species. Soil disturbance caused similar changes to guild structure in both high and low fire intensity plots. Soil disturbance is not recommended as a universal treatment following the clearance of dense stands of aliens. Used in conjunction with indigenous sowing, it may improve restoration at long-invaded, deep-soil sites, following fires of unnaturally high intensity. Post-fire soil disturbance should promote species richness in seedling recruits, plant growth conditions and the development of vegetation cover, while sowing would increase plant density and re-introduce guilds not present in relict soil seed banks.

South African Journal of Botany 67 (4) 2001, 540-551

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The genus Salsola (Chenopodiaceae) in southern Africa: Systematic significance of leaf anatomy

HGWJ Schweickerdt Herbarium, Department of Botany, University of Pretoria, Pretoria 0002, South Africa

* Corresponding author, e-mail: [email protected]

Received 19 August 2000, accepted in revised form 24 February 2001

Almost 90 species of Salsola L. are believed to occur in southern Africa. Correct identification of the different species is, however, rendered problematic by the great morphological similarity of almost all the species, uncertainties concerning the specific status of several entities and the unsatisfactory infrageneric classification of the group. A comparative anatomical study of the leaves of southern African Salsola species was conducted using LM and SEM techniques. The leaf anatomy of southern African Salsola species shows a variation on the typical Salsoloid-type Kranz-anatomy, in that the palisade mesophyll and bundle sheath are not continuous around the leaf, but only present abaxially. Leaf anatomy, particularly the structure of the leaf in transverse section and the type of the indumentum, proved to be very useful for delimiting groups within the genus. The investigated species can be primarily divided into two main groups, according to the presence or absence of a uniseriate adaxial hypodermis. A secondary division can be made by using four main indumentum types, based on the appearance of the abaxial leaf surface. Species possessing one indumentum type can be further subdivided according to the area of the leaf covered by trichomes and the number of elongated cells in the trichomes. There is a weak association between leaf type and hitherto proposed subsections, as well as between leaf type and indumentum type. In general species possessing an adaxial hypodermis tend to have a denser indumentum than species lacking one.

South African Journal of Botany 67 (4) 2001, 552-572

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The lichens of Marion and Prince Edward Islands

DO Øvstedal¹ and NJM Gremmen²*

1 Botanical Institute, Allégaten 41, N-5007 Bergen, Norway

* Corresponding author, e-mail: [email protected]

Received 7 June 2000, accepted in revised form 18 February 2001

A total of 100 lichen species are listed for the islands. Six species are described as new to science: Arctomia subantarctica Øvstedal, Arthothelium evanescens Øvstedal, Coccotrema stellata Øvstedal, Ramonia subantarctica Øvstedal, Thelocarpon subantarcticum Øvstedal and Verrucaria umbilicata Øvstedal. Four new combinations are made: Amandinea subplicata (Nyl.) Øvstedal, Poeltinula cerebrinella (Nyl.) Øvstedal, Verrucaria nigra (Müll. Arg.) Øvstedal (from Cape Horn) and Verrucaria tesselata (Dodge) Øvstedal (from Heard Island). One third of the islands' lichen species also occur in the Northern Hemisphere. Of the Southern Hemisphere species, 24 are exclusively known from areas to the east of the islands (Kerguelen Province Islands, Australia, New Zealand, contrasting to only six species recorded exclusively to the west (South Georgia, Antarctic Peninsula). This suggests a distribution against the present predominantly westerly winds. The large number of seemingly endemic species is suggested to indicate the incomplete knowledge of the lichen floras of the sub-Antarctic islands.

South African Journal of Botany 67 (4) 2001, 573-594

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Vegetation of the Tembe Elephant Park, Maputaland, South Africa

WS Matthews¹, AE van Wyk²*, N van Rooyen² and GA Botha³

1 Tembe Elephant Park, KwaZulu-Natal Nature Conservation Service, Private Bag X356, KwaNgwanase 3973, South Africa

2 Department of Botany, University of Pretoria, Pretoria 0002, South Africa

* Corresponding author, e-mail: [email protected]

Received 10 March 2000, accepted in revised form 24 February 2001

A hierarchical classification, vegetation map, description and ecological interpretation of the plant communities of the Tembe Elephant Park and surrounding areas are presented. The study area falls within the Maputaland Centre of Endemism, which is part of the Maputaland-Pondoland Region, a centre of plant diversity rich in endemic plants and animals. Sixty-four sample plots were distributed in a stratified manner throughout the study area. A TWINSPAN classification, refined by Braun-Blanquet procedures, revealed eight distinct, mainly woodland plant communities. Much of the vegetation distribution can be ascribed to vegetation dynamics and the geomorphological evolution of the region. Dynamics of water in the landscape either directly or indirectly, through its role in moisture levels and soil formation, plays a role in the determination of plant communities at the higher levels. The proposed classification and general descriptions can be used for nature reserve management, land-use planning and further research. Ordinations based on floristic data give an indication of floristic and associated habitat and environmental relationships. Soil character and moisture differences are usually slight, hence the sand-based communities do not have distinct boundaries, except for Sand Forest. Indications are that in the case of Sand Forest the distinct boundary zone of nearly bare soil may well be the result of allelopathy. Eighty-four Maputaland Centre plant endemics/near-endemics were recorded for the study area, with Sand Forest being the most prolific habitat for such taxa, many which appear to be neoendemics. Because of its hypothesised origin (especially lack of specific historic events) and vegetation dynamics, the inclusion of Sand Forest in conservation areas is no guarantee of the future persistence of this rare vegetation type.

South African Journal of Botany 67 (4) 2001, 595-608

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Syntaxonomy and environmental gradients of the grasslands of the Stormberg / Drakensberg mountain region of the Eastern Cape, South Africa

DB Hoare¹* and GJ Bredenkamp²

1 Agricultural Research Council — Range and Forage Institute, Private Bag X05, Lynn East 0039, South Africa

* Corresponding author, e-mail: [email protected]

Received 20 September 2000, accepted in revised form 26 February 2001

A phytosociological classification of the grassland communities of the Stormberg / Drakensberg mountain chain and surrounding lowlands in the Eastern Cape is presented. The study area was firstly stratified on the basis of Acocks's (1988) Veld Types and then within Veld Types on local topography. An initial classification was derived by using two-way indicator species analysis (TWINSPAN) followed by table refinement according to the methods and techniques of the Braun-Blanquet school of phytosociology. Seven grassland associations and eleven sub-associations are formally described. Syntaxa are described using diagnostic floristic elements and characterised using habitat criteria. Annual rainfall and elevation related strongly to floristic gradients, and substrate and slope inclination accounted for local vegetation floristic and structural differences. Species richness was found to be highest in associations with high structural diversity and species turnover was strongest where environmental heterogeneity was high.

South African Journal of Botany 67 (4) 2001, 609-614

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Characterisation of the pitch canker fungus, Fusarium circinatum, from Mexico

H Britz^1†, TA Couhnho¹*, TR Gordon² and MJ Wingfield¹

† Present address: Onderstepoort Veterinary Institute, Private Bag X5, Onderstepoort 0110, South Africa

2 Department of Plant Pathology, University of California, Davis, California 95616, USA

* Corresponding author, e-mail: [email protected]

Received 29 August 2000, accepted in revised form 27 February 2001

Fusarium circinatum (=F. subglutinans f. sp. pini) is the causal agent of pitch canker of pines. This fungus occurs in the United States, Japan, Mexico and South Africa and it can be introduced into new areas on seed and infected plant material. Its presence in cones from symptomless trees is of concern, particularly with respect to seed transmission. In this study, isolates of Fusarium spp. were collected from Pinus patula, P. greggii, P. teocote and P. leiophylla trees in Mexico, showing typical symptoms of pitch canker, as well as from cones from apparently healthy trees. Morphological characteristics of the pitch canker fungus and isolates of F. subglutinans from other hosts are very similar. Therefore, pathogenicity tests, sexual compatibility studies and histone H3-RFLPs were used to characterise isolates. Isolates collected from Pinus spp. from Mexico were identified as F. circinatum. In this study we have thus confirmed that F. circinatum occurs on pines in Mexico and that the affected trees can be asymptomatic.

South African Journal of Botany 67 (4) 2001, 615-619

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Some physical factors affecting adsorption of heavy metals from solution by dried brown seaweed material

WA Stirk* and J van Staden

* Corresponding author, e-mail: [email protected]

Received 3 August 2000, accepted in revised form 27 February 2001

The use of derived seaweed products is gaining support as an alternative cheap method for the remediation of industrial wastewater. Adsorption properties of dried Ecklonia maxima (Osbeck) Papenf., Laminaria pallida ex. J. Ag. and Kelpak waste, the waste product from the manufacture of a commercial seaweed concentrate made from E. maxima, were investigated. The ratio of algal biomass to the initial ion concentration affects ion adsorption. At low ion concentrations, small amounts of sorbent gave the best results. At high ion concentrations, more sorbent was required for maximum uptake. The size of the sorbent particles affects the initial rapid ion sequestration. Smaller sized sorbent particles showed more rapid adsorbance. However, the final ion concentration taken up after 24 hours was not affected by particle size. It is necessary to agitate the sorbent for maximum adsorbance to occur but the rate and method (stirring versus shaking) of agitation had no effect.

South African Journal of Botany 67 (4) 2001, 620-628

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Differences in seed germination of wild and domesticated common bean (Phaseolus vulgaris L.) in response to storage

M López Herrera¹, JR Aguirre Rivera², C Trejo³ and CB Peña-Valdivia³*

1 Fisiología Vegetal, Colegio de Postgraduados. Carretera México-Texcoco, km 36.5 Montecillo, México 56230

2 Instituto de Investigación de Zonas Desérticas, UASLP, San Luis Potosí, México

3 Botánica, IRENAT, Colegio de Postgraduados. Carretera México-Texcoco, km 36.5 Montecillo, México 56230

* Corresponding author, e-mail: [email protected]

Received 22 November 2000, accepted in revised form 2 March 2001

This study compared the effect of storage on the germination of wild and domesticated common bean (Phaseolus vulgaris L.). Two sizes (large and small) of intact and mechanically scarified seeds of wild common bean from Saltito, Durango and La Malinche, Tlaxcala, Mexico, and the cultivars Bayo Mecentral and Amarillo were stored at 30°C and 75% RH for 0, 30, 60 and 90 days. Germination in the dark at 25°C was evaluated. In general, mechanical scarification at zero days of storage induced a reduction in the time to the start of germination (5 to 83h) and in the time to complete germination (126 to 341h) of wild seeds, but it did not affect the percentage of germination. After 30d of storage the germination of small intact wild seeds from Tlaxcala and cv. Bayo Mecentral was reduced to 30%; but after 60d of storage, wild small seeds from Tlaxcala and both cultivars were almost 100% inhibited. In contrast, as an average, intact and scarified wild seeds from Durango and larger seeds from Tlaxcala reached 52 and 25% of germination respectively. Although 90d of storage affected drastically both wild and domesticated beans, even after this long storage, 3 to 15% of wild seeds germinated. The results are consistent with the speculation that an increased sensitivity of common bean seeds to storage under high temperature and elevated RH could be a concomitant result of selection for some other traits such as large seed during domestication.

South African Journal of Botany 67 (4) 2001, 629-635

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The effect of activated charcoal on the production and development of somatic embryos in cultures of carrot Daucus carota

* Corresponding author, email: [email protected]

Received 16 November 2000, accepted in revised form 6 March 2001

The addition of activated charcoal to Murashige and Skoog medium containing 2,4-D resulted in somatic embryogenesis in cultures of Daucus carota. Somatic embryos were not formed in the absence of activated charcoal. In suspension culture, the incorporation of 0.01 to 1.0% activated charcoal to the medium, irrespective of 2,4-D, increased the number of somatic embryos produced. The maximum number of somatic embryos were produced with 1.0% activated charcoal-containing MS medium. Further development of the embryos occurred in the presence of activated charcoal and they regenerated into normal plantlets. Addition of 3.0% activated charcoal to the medium resulted in the formation of abnormal somatic embryos. These embryos produced abnormal plantlets.

South African Journal of Botany 67 (4) 2001, 636-640

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Does smoke substitute for red light in the germination of light-sensitive lettuce seeds by affecting gibberellin metabolism?

MJ Gardner, KJ Dalling, ME Light, AK Jäger and J van Staden*

* Corresponding author, e-mail: [email protected]

Received 9 January 2001, accepted in revised form 8 March 2001

Plant-derived smoke extracts are known to stimulate seed germination in a number of species, but the active compound(s) and mechanism remain unknown. The key to understanding the process underlying the induction of germination lies in the characterisation of the relationship between temporal patterns of physiological and developmental changes. Germination time-course studies revealed that the onset of germination in smoke-treated Grand Rapids lettuce seeds was delayed compared to seeds treated with red light or gibberellic acid. Both red light and smoke-induced germination can be reversed by far-red light, but the escape time is shorter for smoke-treated seeds. Paclobutrazol and AMO 1618, inhibitors of gibberellin biosynthesis, decreased the germination of smoke-treated seeds significantly at concentrations of 0.1 and 1mM, but did not substantially diminish germination of red light-treated seeds. Levels of endogenous gibberellins, estimated using the dwarf rice microdrop assay, were significantly higher in red light-treated seeds than in controls, and peaked after 100% germination was obtained. In contrast, the level of gibberellins in smoke-treated seeds remained low initially, but rose concurrent with the start of germination. The peak level of gibberellins in smoke-treated seeds was markedly higher than in red light-treated seeds. Gibberellin synthesis is thus considered to be a likely component of the mechanism underlying smoke-induced germination.

South African Journal of Botany 67 (4) 2001, 641-654

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Terrestrial habitats on sub-Antarctic Marion Island: their vegetation, edaphic attributes, distribution and response to climate change

VR Smith¹*, M Steenkamp¹ and NJM Gremmen²

1 Department of Botany, University of Stellenbosch, Private Bag 1, Matieland 7602, South Africa

* Corresponding author, e-mail: [email protected]

Received 21 November 2000, accepted in revised form 6 April 2001

The vegetation, soil chemistry characteristics and altitudinal distributions of 23 habitats in 7 habitat complexes on sub-Antarctic Marion Island (47°S, 38°E) are described. The habitat complexes (number of habitats in complex) are: Coastal Salt-spray Complex (2); Fellfield Complex (2); Slope Complex (6); Biotic Grassland Complex (3); Biotic Herbfield Complex (3); Mire Complex (6); Polar Desert Complex (1). The habitat classification closely reflects the between-habitat variation in the relative magnitudes of the main forcing variables that determine ecological succession on the island (moisture, exposure, parent soil material, salt-spray and manuring and trampling by seals and seabirds). Hence, it can serve as a framework against which to detect and evaluate ecological responses to the marked climatic change currently occurring in the sub-Antarctic. Suggestions are made on how the habitats might respond to climatic change (warming, drying) and other perturbations (increasing or decreasing influences of salt-spray and manuring).

South African Journal of Botany 67 (4) 2001, 655-660

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Interaction of osmotic and temperature stress on transgenic soybean

JA de Ronde^1,2*, WA Cress³ and J van Staden²

1 ARC — Roodeplaat Vegetable and Ornamental Plant Institute, Private bag X293, Pretoria 0001, South Africa

2 Research Centre for Plant Growth and Development, University of Natal Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa

*Corresponding author, email: [email protected]

Received 11 January 2001, accepted in revised form 17 April 2001

The triphenyltetrazolium chloride (TTC) assay is based on the ability of viable cells to metabolically reduce tetrazolium salts to formazan. It was used as a method to screen the viability differences of soybean plants transformed with a P5CR gene in antisense direction controlled by an inducible heat shock promoter (IHSP). Differences were detected between the transgenics and the control plants using this method. The transgenics exhibited a sensitive reaction in that formazan production was reduced following an osmotic stress treatment. The control plants however exhibited a tolerant reaction in that formazan production was highest during stress treatment. The efficiency of protein synthesis in the transgenic plants was lower than in the control plants when the inducible heat shock promoter was activated. This indicated that underexpression of the P5CR gene resulted in declined protein synthesis due to proline shortage. The transgenics had a lower seed production than the control plants indicating that the antisense P5CR gene also influenced seed production negatively. The screening methods showed that the control plants were the most viable of the plants tested. The decrease in the proline level due to the activated antisense P5CR gene yielded plants that are directly or indirectly more sensitive to osmotic stress. It appears that the antisense transgenics were not able to withstand the osmotic stress due to the decline in proline synthesis. These findings indicate that proline plays an adaptive role during osmotic stress in soybean plants

South African Journal of Botany 67 (4) 2001, 661-666

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Uptake of [³H]DHZ by tomato seedlings

GD Arthur, AK Jäger and J van Staden*

* Corresponding author, email: [email protected]

Received 12 December 2000, accepted in revised form 23 April 2001

[³H]DHZ applied to intact roots of Lycopersicon esculentum seedlings was taken up faster from plants growing in soil than in liquid medium. However, subsequent export to the shoots was slower from roots growing in soil. Radioactivity was detected in an unlabelled medium into which seedlings that had been cultured in labelled solution for three days were subsequently transferred. Radioactivity taken up by one half of a split-root system moved into the unlabelled root half and then into the unlabelled medium in which it was growing. The current results provide evidence for metabolism of cytokinins in various media, uptake from the media, subsequent transport and metabolism in the shoots. Of interest is that radioactivity was also released from the roots. There is clearly a need to pay greater attention to 'circulatory' movement of cytokinins between plant roots and the environment in which they are growing.

South African Journal of Botany 67 (4) 2001, 667-670

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Short Communication

1 Department of Plant Production and Soil Science, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria 0002, South Africa

* Corresponding author, e-mail: [email protected]

Received 20 September 2000, accepted in revised form 30 May 2001

Lachenalia species are mainly winter and spring flowering bulbous plants endemic to South Africa and Namibia and representatives of the Hyacinthaceae. The annual growth cycle of most species is characterised by active leaf growth during autumn, flowering during winter or spring, followed by leaf senescence and a dormant period during the hot dry summer. Being a fairly new introduction to the flower market, there is a demand for high quality, marketable size bulbs, but due to the lack of information regarding bulb growth and structure, there is a great need for further research. The plants normally have a typical rhythmic, sympodial, modular growth. At the time of planting the bulbs consisted of a swollen bulb scale (cataphyll) and two swollen leaf bases (euphyll) of the previous module surrounding the initials of the new module consisting of two cataphylls, two euphyll primordia and an inflorescence primordium. No 'supernumery bulblets' were observed in this cultivar, but at the end of the growing cycle daughter bulbs were detected in the axils of the swollen leaf bases.

South African Journal of Botany 67 (4) 2001, 671-672

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Book Review

Guide to Standard Floras of the World

 

I could not resist prefacing this review with the observation by EO Wilson that the description and mapping of the world biota is scientifically more important and far more urgent for human welfare than the current focus on phylogentic reconstruction. It is an embarrassing reality that we still have no consensus on the number of species of angiosperms, the best-known group of plants. Estimates range from 215 000 (Cronquist 1988) to as many as 320 000 (Prance et al. 2000), with little hope of achieving a more accurate estimate. One of the main reasons for this deficiency is simply the time-consuming nature of monographs and revisions. It is in this light that I compliment Frodin on monographing the world’s Floras.

This book is nothing less than an annotated bibliography of the more useful standard, or nominally complete, floristic works on vascular plants that covers the entire world, region by region. The first edition of this work was published just over 15 years ago but it is a gratifying observation that, in the twenty years since coverage for this edition was closed, floras and related works have continued to appear, improving coverage for many parts of the world. The current edition has a cut-off date at 1999. With some exceptions, no detailed coverage of florulas or local lists is provided and limited attention has been given to weeds and poisonous or useful plants. In contrast, some ecological classes (somewhat sententiously referred to as physiographic or sinusial isolates), such as alpine zones and wetlands, are included.

The work kicks off with an extensive expose on its scope, sources and structure, including an interesting but unfortunately dated map (circa 1980) showing the approximate state of world floristic knowledge at the time. The most practical part of this chapter is the very necessary explanation of the plan and philosophy of the work. The world’s floras are divided into a three-tier hierarchical system, starting with a breakdown into 10 geographic divisions, corresponding largely to continents or subcontinents. Within each of these divisions are various regions (sometimes grouped into super-regions), corresponding to large countries or areas of comparable size, which in turn comprise units, generally corresponding to smaller countries or states. A parallel system of ecological units is also recognised at the level of the divisions, covering such treatments as Hedberg (1957) Afroalpine vascular plants or Davies and Gasse (eds) (1988) African wetlands and shallow water bodies. With some application one soon gets the hang of this system but, necessary as it was to devise, I suspect the average user will be better served by referring directly to the Conspectus of categories that precedes the treatment of each of the divisions.

Then follows a very scholarly chapter on the evolution of Floras. Frodin, in a synthetic tour de force that highlights his extraordinary familiarity with the subject, thoroughly covers the history and development of Floras. The rise of the age of information technology does not escape his notice, including the development of the PRECIS database by the National Botanical Institute. He ends with the pediction that Floras of the twenty-first century will not be merely on-line in electronic form but entirely absorbed into floristic information systems, with the more traditional forms comprising just some of its products. This is certainly likely but I would feel more comfortable if there seemed to be any surety that the compilation of up-to date Floras could keep pace with the development of the information systems that will disseminate them. Chapter 3 focuses on the philosophy, progress and prospects of Floras at the end of the twentieth century. One of the more pertinent points to emerge here is that Floras are useful only if they are accessible to the users. Two of the keys to this are less jargon and more illustrations.

A mammoth 840 pages forms the main body of the work. The treatment for each geographic subdivision starts with a few useful statistics where these are available, usually land area and number of vascular plant species, accompanied by notes on the status of knowledge of its flora and any available bibliographies. Then follows an annotated listing of the most modern, more or less complete Flora treatments. The annotations that accompany each entry are wonderfully thorough and give a very good indication of what each treatment comprises. I was pleasantly astonished to even encounter a separate listing for the Kruger National Park. Unfortunately what emerges is that the coverage of southern Africa’s flora is not as good as might be expected. It is sobering to read, for instance, that despite the initiation of the Flora of southern Africa in 1963, ‘by 1990—91 only a relatively small proportion of the flora had been covered’. Admittedly various further treatments have appeared since then and, of course, this analysis does not take into account the wonderful variety of taxon-based treatments that have been published for the region. But the point is well made. A selection of apposite quotations taken from various publications appear at the start of each chapter as a light counterpoint to the more ponderous text that follows. Two appendices appear after the main body, listing respectively the major bibliographies, catalogues etc. that are available, and the abbreviations of serials cited. These are followed by an addendum of more recent works that appeared while the book was in proof and I, pardonably, was delighted to see that the announcement of the imminent appearance of Goldblatt and Manning (2000) Cape Plants did not escape Frodin. The book closes with geographical and author indices. Altogether it is an extraordinary achievement.

 

John Manning

Compton Herbarium, National Botanical Institute, Private Bag X7, Claremont 7735, South Africa

e-mail: [email protected]