Recurrent hybridisation events between Primula vulgaris, P. veris and P. elatior (Primulaceae, Ericales) challenge the species boundaries: Using molecular markers to re-evaluate morphological identifications

5 June 2018

Tendal, Kira; Ørgaard, Marian; Larsen, Bjarne; Pedersen, Carsten

Three Primula species, Primula vulgaris, P. veris and P. elatior, have been objects of fascination for gardeners and botanists over several centuries. The species are able to hybridise, and where they co-occur, hybrids are commonly found. In Denmark, Møns Klint on the island of Møn and Købelev Skov on Lolland are examples of localities where all three species occur and where the hybrids P. ×digenea, the hybrid between P. vulgaris and P. elatior, and P. ×polyantha, the hybrid between P. veris and P. vulgaris, can also be found. To investigate relations between the species and their hybrids, 168 specimens from 10 geographical locations were sampled for genetic analysis using DNA markers and identified based on morphological traits, primarily inflorescense structure, the size, shape, colour and markings of corolla and leaf basis, leaf blade texture and hairiness. After identifying species-specific SNPs in the internal transcribed spacer sequence, these were used to resolve species and hybrid boundaries and status through a cleaved amplified polymorphic sequence assay. Polymorphisms in the chloroplast trnL sequence were used as a high-throughput marker and used to determine the maternal parent of hybrids. Ten simple sequence repeat markers were applied to obtain further insight into the genetic makeup of the accessions using Structure and Introgress, providing information of genetic variability within and between populations.
Data analyses indicated that backcrossing of P. ×digenea hybrids with parental species has occurred, and that many of the P. ×digenea found in the study were later-generation hybrids rather than F1s. Analyses of P. ×polyantha specimens show mostly the expected pattern for primary hybrids but indications of P. veris ancestry of a P. vulgaris plant was discovered. Our results further indicate that some of the specimens initially identified as P. elatior include P. vulgaris among their progenitors and thus challenge currently accepted species boundaries.