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Background: While polyploids are common in plants, the evolutionary history and natural dynamics of most polyploid groups are still unclear. Owing to plentiful earlier systematic studies, Ludwigia sect. Isnardia (comprising 22 wetland taxa) is an ideal allopolyploid complex to investigate polyploid evolution and natural dynamics within and among taxa. With a considerable sampling, we concentrated on revisiting earlier phylogenies of Isnardia, reevaluating the earlier estimated age of the most recent common ancestor (TMRCA), exploring the correlation between infraspecific genetic diversity and ploidy levels, and inspecting interspecific gene flows among taxa. Results: Phylogenetic trees and network concurred with earlier phylogenies and hypothesized genomes by incorporating 192 atpB-rbcL and ITS sequences representing 91% of Isnardia taxa. Moreover, we detected three multi-origin taxa. Our findings on L. repens and L. sphaerocarpa were consistent with earlier studies; L. arcuata was reported as a multi-origin taxon here, and an additional evolutionary scenario of L. sphaerocarpa was uncovered, both for the first time. Furthermore, estimated Isnardia TMRCA ages based on our data (5.9 or 8.9 million years ago) are in accordance with earlier estimates, although younger than fossil dates (Middle Miocene). Surprisingly, infraspecific genetic variations of Isnardia taxa did not increase with ploidy levels as anticipated from many other polyploid groups. In addition, the exuberant, low, and asymmetrical gene flows among Isnardia taxa indicated that the reproductive barriers may be weakened owing to allopolyploidization, which has rarely been reported. Conclusions: The present research gives new perceptions of the reticulate evolution and dynamic nature of Isnardia and points to gaps in current knowledge about allopolyploid evolution. [ABSTRACT FROM AUTHOR]

Ypsilandra thibetica Franch. (Liliaceae sensu lato), previously known only from southcentral and southern China (Sichuan, S. Hunan and NE Guangxi), was recently found in mountainous regions of central and eastern Taiwan. The discovery adds a new record for the species, and for the genus, to the flora of Taiwan. Ypsilandra can be easily distinguished from other genera of Liliaceae by its rosette of basal leaves, racemose inflorescence, and 3-lobed capsules. This paper provides a taxonomic account of the genus, a line drawing and color photographs to aid in identification. The somatic chromosome number and karyotype formula (2n = 34 = 18m+10sm4SC+6st2SC ) are reported for Y. thibetica for the first time. [ABSTRACT FROM AUTHOR]