Iris cryptoruthenica sp. nov. (Iridaceae): a cryptic lineage within the morphotype Iris ruthenica revealed by chloroplast and rDNA barcoding and karyosystematic evidence

Iris ruthenica is a widespread Siberian species occurring in both boreal forest and steppe habitats, yet its genetic structure has remained poorly understood. During a survey of I. ruthenica in the Altai Mountain Country, we detected a cryptic lineage that is morphologically indistinguishable from I. ruthenica s. str. but differs in chromosome number. All Russian populations examined to date have 2n = 84, whereas the cryptic lineage has 2n = 42, and flow cytometry shows a corresponding difference in genome size (1C = 4.025 ± 0.110 pg vs. 1C = 2.135 ± 0.020 pg). Comparative analyses of chloroplast markers spanning the atpB–accD and rpl2–matK intervals (including atpB, accD, psbA, rbcL, rpl2, rps19, matK, and ycf1) revealed a p-distance of ~ 0.5 % between the two lineages, a level of divergence that falls within the range observed between recognized Iris species. Polymorphisms in nuclear rDNA (18S–ITS1–5.8S–ITS2–28S) further support their genetic distinctness. Several plastid haplotypes were detected within I. ruthenica, but none differentiated its varieties (var. nana, var. brevituba) or its close relative I. uniflora. Although no consistent morphological differences were detected, we found compelling molecular evidence supporting the recognition of this lineage as a distinct species, which is formally described here as I. cryptoruthenica. Based on current data, its known range includes the Altai Mountain Country and northern China (Xinjiang).