Morphometric analysis of floral variation in the Pyrola picta species complex (Ericaceae): interpretation and implications for ecological and phylogenetic differentiation DIANA D. JOLLES* Rancho Santa Ana Botanic Garden, Claremont Graduate University, 1500 North College Avenue, Claremont, CA 91711, USA Received 27 June 2014; revised 15 November 2014; accepted for publication 12 December 2014 The Pyrola picta species complex of western North America comprises four species (P. picta, P. dentata, P. aphylla and P. crypta) that grow sympatrically in some parts of their collective ranges, have remarkably similar flowers and share pollinators. These species do not exhibit the genetic signatures typical of random or heterospecific mating, but instead show genetic divergence patterns indicating that they maintain surprising levels of repro- ductive isolation. To better understand how species boundaries are maintained, the current study uses statistical ordination analyses to determine whether species isolation across shared geographical ranges might be achieved through subtle differences in floral characters among species. The possible contribution of differences in flowering phenology (e.g. temporal reproductive isolation) to reproductive isolation was also evaluated for the small subset of populations in which two or more species occur in direct sympatry. Among species in the P. picta complex, there are both phylogenetic and geographical trends in some floral characteristics, whereas other characters do not covary with either geography or species identity. In several sympatric populations, differences in flowering phenology among species suggest that timing plays a major role in non-random (i.e. mainly conspecific) mating. The conclusions of this study are that reproductive isolation in the P. picta species complex is reinforced by differences in the timing of floral maturation and the morphologies of androecium and floral display characters. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177, 462–480. ADDITIONAL KEYWORDS: anthers – buzz pollination – floral display – North America – phenology – Scotophyllae. INTRODUCTION Gross leaf morphology is typically used to distinguish among taxa in the Pyrola picta Sm. species complex (e.g. Smith, 1814; Hitchcock & Cronquist, 1973; Larrison et al., 1974; Haber, 1993). The four species are distinguished by having green leaves with white mottling along the primary and secondary veins (i.e. P. picta and P. crypta Jolles), dull-green leaves lacking white mottling, with glaucous integument and dentate margins (P. dentata Sm.), or leaves that are highly reduced and lack chlorophyll (P. aphylla Sm.) (Fig. 1). However, overlapping variation in these and other leaf characters (e.g. size, shape, development and function) within and among species has con- founded consistent and confident diagnosis of species (Camp, 1940; Haber, 1987). Both Camp (1940) and Haber (1987) argued, on the basis of the observed continuous variation in both foliar and floral charac- ters, that the P. picta species complex represents a single, polymorphic species rather than three distinct species, as the group was otherwise treated at the time. The evolutionary bases for this variation have not been investigated experimentally and the assign- ment of specimens to particular species using mor- phology alone is sometimes difficult despite recent phylogenetic studies that have resolved the three *E-mail: diana.jolles@gmail.com Botanical Journal of the Linnean Society, 2015, 177, 462–480. With 8 figures © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177, 462–480 462