Clonal growth and clonal reproduction in Asarum europaeum L. subsp. europaeum (Aristolochiaceae) and their relevance for habitat colonisation and maintenance. A morpho-ecological characterisation
published: Aug 12, 2005
Clonal plants like Asarum europaeum are characteristic components of the herb layer of many Central European broadleaved forests. Within these habitats, clonal taxa are often growing in distinct spatially-discrete patches separated from each other rather than forming a continuous cover. For the colonisation and maintenance of these patches and habitats, clonal growth and clonal reproduction [i.e. the disintegration or fragmentation of the plants into physiological and morphological independent units (= ramets)], play important roles, especially in taxa with infrequent sexual reproduction.The morpho-ecological features of both mechanisms are studied in A. europaeum subsp. europaeum var. europaeum (Aristolochiaceae), a common perennial rhizomatous woodland herb. To analyse the clonal architecture and clonal reproduction and to assess their respective relevance for habitat colonisation, patches and clones of the taxon are dug up in natural populations from two mixed broadleaved-beech forests in Thuringia and Saxony-Anhalt (Germany).The taxon is characterised by intense clonal growth. New modules are initiated sympodially each year from the bud in the axil of the uppermost leaf, i.e. near the apical ends of the rhizomatous shoots, but can also develop from lateral buds and shoots originating from the axils of scale leaves from the previous year. By this means, branched networks of connected modules from several successive years are formed. Clonal reproduction also regularly occurs in A. europaeum. Two basic types of severance are frequently observed along the rhizomatous older modules: partial gradual decay and breakage. Both cause the destruction of the spacers between leaf modules and, consequently, result in the separation of ramets (detached former modules). In addition to descriptions, the clonal architecture and especially the characteristics of clonal reproduction in A. europaeum are documented by photographs.Based on the presented data, the roles of clonal growth and clonal reproduction for habitat colonisation and maintenance in A. europaeum are evaluated, and the relevance of this mechanism of "consequent vegetative multiplication" is discussed.