Botanical Journal of the Linnean Society, 2002, 140, 297–311. With 6 figures © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society, 2002, 140, 297–311 297 Blackwell Science, LtdOxford, UKBOJBotanical Journal of the Linnean Society0024-4074The Linnean Society of London, 20022002 140? Original Article REPRODUCTION IN IN RELICT RHODODENDRON PONTICUM J. A. MEJÍAS ET AL. *Corresponding author. E-mail: jmejias@us.es. †Present address: Departamento de Biología. Universidad de Cádiz. Campus Río San Pedro. 11510-Puerto Real, Spain. Reproductive ecology of Rhododendron ponticum (Ericaceae) in relict Mediterranean populations JOSÉ A. MEJÍAS*, JUAN ARROYO and FERNANDO OJEDA † Departamento de Biología Vegetal y Ecología, Universidad de Sevilla. Apartado 1095, 41080-Sevilla, Spain. Received May 2002; accepted for publication August 2002 In the southern Iberian Peninsula, Rhododendron ponticum occurs in restricted and vulnerable populations as a Ter- tiary relict. Population structure and the main phases of the reproductive process were examined in order to shed light on recruitment patterns and limitations. Rhododendron ponticum flowers are self-compatible and attract a diverse array of insects, which are responsible for a considerable number of seeds set in the populations. Neverthe- less, only adults form populations, whilst seedlings are scarce and saplings virtually absent (only two juveniles out of 2489 adults sampled). Non-specialized vegetative multiplication by layering was observed. Recruitment failure seems to depend on the scarcity of safe microsites, which are free from drought, for seedling establishment. The observations contrast with R. ponticum’s reputation as an aggressive invader in temperate Atlantic areas. It is pro- posed that the species shows a variable balance between sexual reproduction and vegetative multiplication depend- ing on environmental conditions. At present, only the latter seems to be prevailing in relict populations in the Iberian Peninsula. This flexible reproductive strategy is also discussed as a mechanism allowing persistence during geolog- ical climatic oscillations. © The Linnean Society of London, Botanical Journal of the Linnean Society, 2002, 140, 297–311. ADDITIONAL KEYWORDS: Bombus – breeding system – clonal plants – Macroglossum – plant extinction – pollination – recruitment – seedling survival – threatened plants – refugia. INTRODUCTION Two key tasks in plant conservation biology are to identify the factors that threaten plant abundance and evaluate the risks of population extinction. Although many factors influence plant abundance, most researchers have concentrated on either ecolog- ical or genetic aspects. However, these approaches are often incomplete because (i) ecological studies fre- quently turn out to be habitat descriptions of the rare species, and (ii) no clear differences are found between rare and widespread species in terms of genetic diver- sity pattern (Schemske et al., 1994; Lewis & Crawford, 1995; Gitzendanner & Soltis, 2000; Podolsky, 2001), despite the theoretical relationship between popula- tion genetic diversity and probability of survival. In addition, few genetic studies have demonstrated prac- tical outcomes for plant conservation (Schemske et al., 1994; Hogbin, Peakall & Sydes, 2000). Some authors have stressed the importance of having knowledge of the reproductive biology and recruitment pattern in endangered species to be able to detect life-cycle stage(s) constituting the limiting phase(s) and to eval- uate causes determining vulnerability (Karron, 1991; Schemske et al., 1994). The identification of current causes determining plant rarity and vulnerability has not only a practical use for implementing plant conservation policy, but could also shed light on the historical processes deter- mining area restriction in relict plants. Relict species are supposed to have shown more competitive ability in the past, but have eventually faced changing, adverse environment conditions affecting critical stages of their life cycles, except in a number of sites where particular environmental conditions make per- sistence of these species possible (i.e. refugia). In the Mediterranean basin, a group of relict species repre- sents vestiges of evergreen rain forests that thrived Downloaded from https://academic.oup.com/botlinnean/article/140/3/297/2433669 by guest on 28 June 2022