Duckweeds are small, free-floating, morphologically highly reduced organisms belonging to the monocot order Alismatales. They display the most rapid growth among flowering plants, vary ~ 14-fold in genome size and comprise five genera. Spirodela is the phylogenetically oldest genus with only two mainly asexually propagating species: S. polyrhiza (2n = 40; 160 Mbp/1C) and S. intermedia (2n = 36; 160 Mbp/1C). This study combined comparative cytogenetics and de novo genome assembly based on PacBio, Illumina and Oxford Nanopore (ON) reads to obtain the first genome reference for S. intermedia and to compare its genomic features with those of the sister species S. polyrhiza. Both species' genomes revealed little more than 20,000 putative protein-coding genes, very low rDNA copy numbers and a low amount of repetitive sequences, mainly Ty3/gypsy retroelements. The detection of a few new small chromosome rearrangements between both Spirodela species refined the karyotype and the chromosomal sequence assignment for S. intermedia.

Biology Centre Czech Academy of Sciences Institute of Plant Molecular Biology České Budějovice 37005 Czech Republic

Biology Faculty Dalat University District 8 Dalat City Lamdong Province Vietnam

Institute of Biology Martin Luther University Halle Wittenberg 06120 Halle Germany

Jiangsu Collaborative Innovation Centre of Regional Modern Agriculture and Environmental Protection Huaiyin Normal University Huai'an 223300 China

Jiangsu Key Laboratory for Eco Agricultural Biotechnology Around Hongze Lake School of Life Sciences Huaiyin Normal University Huai'an 223300 China

Leibniz Institute of Plant Genetics and Crop Plant Research 06466 Gatersleben Stadt Seeland Germany

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Personal Perspectives on Plant Ribosomal RNA Genes Research: From Precursor-rRNA to Molecular Evolution

Limitation of current probe design for oligo-cross-FISH, exemplified by chromosome evolution studies in duckweeds

Probably Correct: Rescuing Repeats with Short and Long Reads