ISSN 0968-044 Bulletin of The Natural History Museum THE NATURAL HISTORY 22 KOV 2000 Q6NEKAI LIBRARY THE NATURAL HISTORY MUSEUM VOLUME 30 NUMBER 2 30 NOVEMBER 2000 The Bulletin of The Natural History Museum (formerly: Bulletin of the British Museum (Natural History) ), instituted in 1949, is issued in four scientific series, Botany, Entomology, Geology (incorporating Mineralogy) and Zoology. The Botany Series is edited in the Museum's Department of Botany Keeper of Botany: Dr R. Bateman Editor of Bulletin: Ms M.J. Short Papers in the Bulletin are primarily the results of research carried out on the unique and ever- growing collections of the Museum, both by the scientific staff and by specialists from elsewhere who make use of the Museum's resources. Many of the papers are works of reference that will remain indispensable for years to come. All papers submitted for publication are subjected to external peer review for acceptance. 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The Natural History Museum, 2000 Botany Series ISSN 0968-0446 Vol. 30, No. 2, pp. 33-130 The Natural History Museum Cromwell Road London SW7 5BD Issued 30 November 2000 Typeset by Ann Buchan (Typesetters), Middlesex Printed in Great Britain by Henry Ling Ltd., at the Dorset Press, Dorchester, Dorset Bull. nat. Hist. Mus. Land. (Bot.) 30(2): 33-79 Issued 30 November 2000 The genus Polystichum (Dryopteridaceae) in Africa . ./ " , \") JACOBUS P. ROUX 22 NOV National Botanical Institute, Compton Herbarium, Private Bag X7, Claremont 7735, South Africa igfgKAL CONTENTS LJ6RARV Introduction 33 Materials and methods 34 Terminology 34 Taxonomic treatment 35 Key to the African species of Polystichum (including Marion and Prince Edward Islands) 36 References 78 Systematic index 79 SYNOPSIS. Polystichum Roth is a fern genus of 1 60 to 200 species occurring throughout the temperate parts of the world and the montane tropics, but absent from the arid regions as well as the lowland tropics. Although floristic accounts of Polystichum exist for many parts of the world, the genus remains poorly understood and a taxonomic account for the group as a whole has never been undertaken. Polystichum is poorly represented in Africa (including the Marion Island group) with merely 16 species and one known hybrid having been recorded from the region. Most of the species are confined to sub-Saharan Africa, occurring mainly along the eastern mountain ranges and Mt. Cameroon in the west. In this review of the African Polystichum species detailed observations are presented especially on the paleae, as these structures were found to provide the best characters on which a subgeneric classification can be based. Diagnostic features and relationships, variation, and the distribution and ecology of each species are included. & Also the INTRODUCTION allopolyploids (Vida Reichstein, 1975; Wagner, 1979). frequent occurrence of Fl -hybrids in some groups obscures species limits. consists of The genus Polystichum Roth between 160 (Tryon & A formal subgeneric classification for the genus has thus far only and 200 It occurs Tryon, 1982) (Daigobo, 1972) species. throughout been provided for the east Asian species by Tagawa (1940) and the the as as the montane but temperate parts of world well tropics, Daigobo (1972). Some of these sections have since been subdivided is from the lowland Within the two mostly absent tropics. range further by Zhang & Kung (1995, 1996a, b) and Kung & Zhang distinct centres of can a Asiatic diversity be identified, namely larger (1998) to make provision for some of the Chinese species. Since centre with and a American centre approximately 70 species tropical most species remain poorly known a phylogeny for the genus cannot with approximately 55 species. Both these regions fall within the be proposed. mountainous tropics characterized by mild, moist climates that are Although floristic accounts of the genus have been published for with the areas of hardly seasonal. They also correspond highest many parts of the world, some being very old and outdated, no single species diversity for homosporous ferns (Tryon, 1985). monographic treatment exists and most species remain poorly known. Within the Dryopterideae Polystichum is most closely related to Some of the modern-day regional treatments provide no detailed Arachniodes Blume, Cyrtomium C. Presl, Dryopteris Adans. and observations that may suggest affinities. Within the study area Phanerophlebia C. Presl. Cyrtomium and Phanerophlebia have floristic accounts for Polystichum are available for North Africa often been included in Polystichum (Kramer, 1990), but it has (Maire, 1952), West tropical Africa (Alston, 1959), Cameroon subsequently been shown that both these genera have a closer (Tardieu-Blot, 1964), Mozambique, Malawi, Zambia and Zimba- affinity to Polystichum than to each other (Yatskievych, 1996). bwe (Schelpe, 1970), Rwanda, Burundi and Kivu (Democratic Polystichum in a strict sense is a natural and relatively homogene- Republic of Congo) (Pichi Sermolli, 1985), southern Africa (Schelpe ous group of plants characterized by 1 -pinnate to 3-pinnate laminae & Anthony, 1986) and Bioko (Benl, 1991). with acroscopically developed ultimate segments, anadromous free It is a well-known fact that Africa, when compared with other venation, uni- or biseriate circular sori positioned medially, termi- tropical parts of the world, supports a floristically impoverished nally or near terminally on abbreviated or unabbreviated vein vascular flora. This phenomenon is also reflected in the pteridophyte is ascribed branches, and peltate indusia (a number of species are exindusiate). flora of the continent. The cause of this floristic poverty the The receptacle appears to be nude in most species. to the isolation of Africa from the other continents since mid- Although Polystichum as a genus is easily recognized, many Cretaceous and the subsequent significant changes in the climate as drift aridification caused extra- species are superficially very similar. The delimitation of species is a result of uplift, continental and by further hampered by the fact that many, mostly common species are tropical glaciation. All these changes may well have resulted in a The Natural History Museum, 2000 34 J.P. ROUX progressive elimination of the once rich tropical and subtropical mountain systems, whilst P. transvaalense and P. wilsonii are dis- forests that existed towards the late Jurassic and the establishment of tributed throughout seven mountain systems. The distribution of P. extensive deserts and semi-deserts by the early Pliocene (Coetzee, wilsonii, however, also extends along the Himalaya mountains to 1993). Bhutan, Japan and Taiwan. Polystichum luctuosum has an almost Within the study area two regions can be identified: an African similar eastern distribution but is confined to the Drakensberg and and a sub-Antarctic region. The origin, composition and floristic Chimanimani mountain systems in Africa. Polystichum luctuosum affinities of these regions differ markedly. The African region is the and P. wilsonii also show a disjunct distribution with the Madagascan largest and today there are three fundamentally different floras or region. biogeographical subregions which can be identified: a southern Based on observations taken from the systematic treatment, and African flora, a tropical African flora and a North African flora. judging from wide-ranging species, southern and tropical African The flora of the southern African subregion is believed to have Polystichum has a closer affinity with taxa from Asia than with those evolved gradually since the mid-Tertiary, derived partly from an from the Americas. Polystichum in the North African phyto- ancient southern African temperate flora and partly from a tropical geographical subregion shows a closer affinity with Polystichum African forest flora (Goldblatt, 1978). Elements of the southern from Europe than from Africa as P. aculeatum and P. setiferum are African flora currently extend into tropical Africa along the eastern widespread in that region. Only P. marionense, endemic to Marion, escarpment. The southern Cape forests are believed to be impover- Prince Edward and Crozet Islands, occurs in the sub-Antarctic ished remnants of the tropical African forest flora (Coetzee & phytogeographical region. Muller, 1984). Also the tropical African flora is believed to be an impoverished remnant of a once much richer tropical rainforest flora that extended over a far greater area than it currently occupies. MATERIALS AND METHODS North Africa has also experienced significant changes in its climate and vegetation. During the Palaeocene the present Sahara This review is based on observations made during extensive field- desert was clothed by a rich tropical lowland rainforest that also work in southern Africa and on cultivated plants collected