Evolution and systematics of polyploid Nigritella (Orchidaceae)

Abstract

Members of the orchid genus Nigritella are widespread in European mountains, but species circumscriptions and evolutionary patterns in the genus are subjects to conflicting opinions. We analyzed a representative material of Nigritella for differentiation at nuclear and plastid marker loci. In agreement with predictions from embryological studies, diploid members of Nigritella are sexual and mostly out‐crossing, whereas triploid, tetraploid and pentaploid members are apomicts. The diploid taxa were poorly differentiated in the investigated molecular markers, except for the western N. gabasiana, which was separated in plastid haplotypes. Polyploid Nigritella aggregate into three groups and within each of these groups apomictic polyploids have given rise to new species. Within the N. nigra group, the tetraploid N. nigra subsp. austriaca is somewhat differentiated from the triploid subsp. nigra at nuclear as well as plastid loci. Fusion of an unreduced egg cell from subsp. nigra with a haploid microgamete from Gymnadenia conopsea gave rise to Gymnigritella runei. Within the N. widderi group, N. archiducis‐joannis is poorly separated from N. widderi in molecular markers, and the pentaploid N. buschmanniae has evolved by fusion of an unreduced egg cell from N. widderi with a haploid microgamete from a diploid Nigritella. Within the N. miniata group, N. stiriaca is somewhat differentiated from N. miniata at nuclear loci, but no other segregates of N. miniata are supported at species level. Polyploid Nigritella species accumulate genetic diversity by somatic mutations. In the widespread N. nigra subsp. austriaca and N. miniata this diversity is correlated to geography. Although some polyploids may be of recent origins, each polyploid contain genetic markers no longer encountered in diploid members of the genus. According to plastid marker data, Nigritella and Gymnadenia may constitute monophyletic sister genera.

Morphological, ecological, and molecular phylogenetic approaches reveal species boundaries and evolutionary history of Goodyera crassifolia (Orchidaceae, Orchidoideae) and its closely related taxa

“…Furthermore, genetic variation, which was high in the outcrossing G. schlechtendaliana , was low in the predominantly agamospermous G. crassifolia , both between and within populations. Similar patterns have been observed in other orchids, including Nigritella Rich., which includes both outcrossing and agamospermous species ( Hedrén et al 2018 ).…”

Geographical Parthenogenesis in Alpine and Arctic Plants

“…Widespread generalist clones, however, were found in North American Crataegus [ 82 ]. In the alpine orchid genus Nigritella , high clonal diversity was found, but only with populations in the vicinity sharing the same genotypes [ 54 ]. In general, the influence of genotypic diversity or clonality on GP patterns appears to be less relevant for plants than predicted by classical models.…”

Advances in the Study of Orchidinae Subtribe (Orchidaceae) Species with 40,42-Chromosomes in the Mediterranean Region

“…The above-mentioned genera, known for their high degree of chromosomal diversity and complexity, are among the most extensively studied groups in orchid cytogenetics [13][14][15][16][17][18][19][20][21][22][23][24]. These studies have revealed significant variation among species and lineages in the distribution and abundance of repetitive DNA, which may reflect different modes of chromosomal evolution, including genome duplication and rearrangement [25].…”