Willdenowia 40 – 2010 13 Wolf Bernhard dickoré1* & GerWin kasperek2 Species of Cotoneaster (Rosaceae, Maloideae) indigenous to, naturalising or common- ly cultivated in Central Europe Abstract dickoré W. B. & kasperek G.: species of Cotoneaster (Rosaceae, Maloideae) indigenous to, naturalising or com- monly cultivated in central europe. – Willdenowia 40: 13–45. – online issn 1868-6397; © 2010 BGBM Berlin- dahlem. doi:10.3372/wi.40.40102 (available via http://dx.doi.org/) several alien species of the eurasian genus Cotoneaster are naturalising in central europe, apparently increasingly so, and some on a massive scale. They presumably originate from large-scale cultivation for ground cover, hedges or as ornamental shrubs. The present paper keys and synopses the Cotoneaster species indigenous to, naturalis- ing or commonly cultivated in central europe, on the basis of, relatively limited, both living (wild, adventive and cultivated) and herbarium material. an attempt is made to understand the nature of variation from the genus’ centre of diversification, the mountains of china and the himalayas, which are likewise the origin of most cultivated and naturalising Cotoneaster species. Taxonomic and nomenclatural problems, putatively relating to the presence of apomixis and hybridization in the genus, are discussed. Many of the more than 500 published binomials, including a substantial proportion of those based on cultivated material, seem to be poorly defined, both morphologically and chorologically. of an estimated total of only 50–70 Cotoneaster species worldwide, about 20, mainly chinese spe- cies have been found escaping from cultivation in central europe. presently, about ten species must be considered fully naturalised and, locally at least, invasive. additional key words: taxonomy, ornamental shrubs, alien plants, adventives, neophytes, china Introduction The genus Cotoneaster (Rosaceae, Maloideae) occurs in lar- extensive species inventories were given by flinck & ge parts of mainly continental temperate eurasia (and in- hylmö (1966) and klotz (1982). however, these are cluding northwestern africa, southern india and Taiwan, neither consistent, nor are the vast majority of species excluding Japan). its distribution is often scattered and names accepted or even recognised in regional floras of mainly concentrated in the mountains of the meridional eurasia. a recent monograph by fryer & hylmö (2009) and nemoral zones, while having a clear centre of diver- has added another c. 70 ‘new species’. floras relating sity in china and the himalayas. a probably increasing to central europe (e.g., Jäger & Werner 2005; fischer number of asiatic Cotoneaster species is found alien, es- & al. 2008; kutzelnigg 1994) and larger-scale compila- caping from cultivation or naturalising in central europe. tions (sennikov 2009), as well as garden handbooks and While Cotoneaster is unequivocal in its generic cir- guides to trees and shrubs (schneider 1906; krüssmann cumscription, many species, whether in their native 1976; Bärtels 2001; roloff & Bärtels 2006; Meyer & al. ranges, alien or cultivated, cannot readily be identified. 2006; hrevcova 1999; Jerzak 2007) diverge widely as to The genus is taxonomically difficult, mainly because it nomenclature, circumscription and status of the included comprises nearly 500 published binomials (ipni 2009). species. 1 Botanische staatssammlung München, Menzinger str. 67, 80638 München, Germany; *e-mail: [email protected] (author for correspondence). 2 Universitätsbibliothek Johann christian senckenberg, Bockenheimer landstr. 134–138, 60325 frankfurt am Main, Germany; e-mail: [email protected] 14 dickoré & kasperek: Cotoneaster in central europe The present paper aims at a taxonomic review and texture and indumentum, inflorescence size (number of synopsis of the Cotoneaster species indigenous to, flowers), petal form and colour, fruit size, form, colour, commonly cultivated or naturalising in central europe. indumentum and number of nutlets included. Taxonomic problems in the genus, apparently, relate to Growth forms encompass a wide range of differently several specifics or syndromes, which need to be ad- sized and formed shrubs, ranging from low carpets or dressed in some detail: (a) Cotoneaster is poor in clear- creepers to almost treelike types. however, constructive cut morphological characters; (b) it is of great horticul- features are difficult to describe and also highly variable tural interest and many species were described on the with age and ecology. basis of cultivated strains, often with unknown or cor- leaf duration is an important character, while appar- rupt provenances; (c) native distribution and variation ently in some species ecologically controlled. sometimes of many taxa are poorly known; and (d) indiscriminate deciduous and evergreen types are morphologically al- numbers of species have been described in assuming most indistinguishable. apomixis and hybridisation, but probably often on an indumentum of leaves is often distinctive, while the insufficient factual basis. upper (adaxial) surface often soon becomes glabrous and the lower (abaxial) surface commonly remains strigose or tomentose. Material and methods flower morphology discriminates, possibly not quite The present study is based on a relatively limited material consistently so, between the two subgenera: Cotoneaster from five domains. subg. Cotoneaster has small pink red-tinged or red, cup- (1) native and alien Cotoneaster species of central or bowl-shaped flowers, with petals erect or incurved, europe were studied in the field, mainly in, but not lim- cuneate at base and often erose-dentate along the mar- ited to, the surroundings of Göttingen, southern lower gin; the flowers of C. subg. Chaenopetalum (koehne) G. saxony, and Munich, southern Bavaria, Germany. (2) klotz (in Wiss. Z. friedrich-schiller-Univ. Jena, Math.- herbarium material was revised in the herbaria (abbre- naturwiss. reihe 10: 77. 1982) are mostly white (some- viations according to Thiers 2009) B, hal, hBG, Je, times pink), fully opening stellate, with petals patent, M, MsB, WU and the private herbarium of p. pilsl (salz- often distinctly stalked and mostly entire. probably all burg). images of mainly type specimens were consulted species of Cotoneaster flower for only a very short pe- on the respective platforms of some major herbaria in- riod of time, in spring or early summer, while ripe fruit is cluding a, Gh, k and pe. additional images were ob- present in autumn only, with characters mainly discrimi- tained from specimens deposited at a, dd, Gh and lZ. nating between red or black-coloured, in form, pubes- (3) living accessions were studied in the botanical gar- cence and by number of nutlets included. dens of Berlin, Göttingen, halle and Munich, and in the private garden of G. klotz, Jena. (4) We have collected Taxonomic constraints and examined several species in the field during expedi- tions in china and the himalayas. (5) The literature and acknowledging that it is virtually impossible to have online resources were scanned for diagnostic characters, flowers and fruit on the same Cotoneaster specimen, distribution, other biological features and reports of alien while all traditional dichotomous keys require both for occurrences. identification, some general taxonomic dogmas need Given the huge number of described species and ap- to be scrutinised. it is obvious that the same constraint parent taxonomic ambiguities in Cotoneaster, the present must apply for the bulk of type specimens and original study must remain provisional. The whole genus needs a descriptions in the genus. Theoretically, some related major taxonomic revision including type studies, which caveats can be overcome by repeated visits to a living could only to a minor extent be accomplished within the individual, through cultivation or by considering sec- present framework. furthermore, naturalisations of vari- ondary sources. ous species seem an ongoing, probably also recently ac- in fact, much of the taxonomic information about Co­ celerating process. toneaster is based on either incomplete herbarium speci- mens or on cultivated material. however, the extensive horticultural career of the genus seems to have created Morphology a suite of new problems. an immense pool of cultivated The genus Cotoneaster consists entirely of unarmed selections, forms, strains, mutations or hybrids, often shrubs. as an almost exclusive character, the leaves are with unknown or corrupt provenances and histories, always entire, while otherwise the range of variation re- has emerged in the gardens. in turn, this same stock has sembles that of related genera (Crataegus, Pyracantha, served, deliberately, by chance or by necessity, to amend Sorbus). Morphological characters used to distinguish descriptions and to describe scores of ‘new species’. it, Cotoneaster species are mostly difficult to classify, i.e., thus, seems amazing that, again, the same stock of prob- often variable within wide ranges but between few dis- ably billions of (in europe) cultivated chinese Cotoneas­ crete states. They include growth form, leaf size, form, ter plants gave rise to naturalisations of only a handful of Willdenowia 40 – 2010 15 fairly well-marked species, which mostly are unequivo- seed progeny. a ‘new species syndrome’ (fraser-Jenkins cal among different botanists and sources. 1997), as also evident in Cotoneaster, is then obviously While we have to offer little more than some lucky justified by claiming